JPH1174793A - Signal transmission method via one bit digital signal, delta-sigma modulation circuit and demodulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal transmission method via one bit digital signal, a delta-sigma modulation circuit and a demodulation circuit capable of transmit ting a main signal by adding a sub-signal to it with a simplified circuit. SOLUTION: An inputted signal is modulated by delta-sigma and the one bit digital signal is outputted by the delta-sigma modulation circuit 31. Multiplier coefficients of respective loop gain changing circuits 11a to 11c are controlled based on channel information and a loop gain of a partial negative feedback loop provided in the delta-sigma modulation circuit 31 is selected by an additional information signal generation circuit 10. As a result, shape of quantization noise distribution of the one bit digital signal is selected by the channel information. The channel information is extracted from change of the shape at a demodulation side. Consequently, the sub-signal is added to the main signal without imparing the characteristic of the one bit digital signal to be demodulated with the simplified circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission method using delta sigma modulation, a delta sigma modulation circuit, and a signal generated by delta sigma modulation, which are particularly preferably used for audio signal processing. The present invention relates to a bit digital signal demodulation circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of transmitting a digital signal, a multi-bit encoding method in which one word composed of a plurality of bits is transmitted as a delimiter and a 1-bit digital signal using delta-sigma modulation have been used. A transmission method is known.

[0003] In the case of the multi-bit encoding method, the transmitting or recording side transmits one data according to a predetermined format.
Encode to words. On the other hand, the receiving or reproducing side establishes word synchronization to determine the delimitation of each word, and decodes each word to identify data. Therefore, a signal processing circuit that performs signal processing according to the word format is required on both sides. As a result, once the word format is determined and the sampling frequency, dynamic range, etc. are standardized, it is difficult to change the standard. Furthermore, since the method requires word synchronization,
An error correction circuit for correcting an error that is easily affected by a transmission path or the like is indispensable.

On the other hand, in the 1-bit digital encoding method, since the 1-bit digital signal is a finely divided data flow that does not require word synchronization, the 1-bit digital signal is hardly affected by a transmission path or the like, and is less susceptible to errors. It has the advantage of being strong.
Therefore, in this system, an error correction circuit is not required in both the transmitting or recording device and the receiving or reproducing device. Further, when the 1-bit digital signal is an acoustic signal, the receiving or reproducing side can demodulate the 1-bit digital signal into an analog signal by a simple low-order low-pass filter, so that a complicated processing circuit is not required for demodulation. Become. Therefore, in recent years, a 1-bit digital encoding scheme, which has many advantages as compared with a multi-bit encoding scheme, has attracted attention.

As shown in FIG. 8, in a conventional typical delta-sigma modulation circuit 100, an analog acoustic signal input from an input terminal 101 is integrated by integrators m101 to m107 connected in cascade. . After the outputs of the integrators of each stage are added by the adder 103, the quantizer 104
Is input to The quantizer 104 derives an output of “1” to the output terminal 106 when the output of the adder 103 is 0 or more, and derives an output of “0” when the output of the adder 103 is less than 0. The output of the quantizer 104 is negatively fed back to the input side of the first-stage integrator m101 via the digital / analog converter 105 and the feedback resistor r100.

On the other hand, a dip is formed in the quantization noise distribution (noise floor) of the 1-bit digital signal output from the delta-sigma modulation circuit 100 and the delta sigma is adjusted in order to adjust the quantization noise distribution shape to a desired shape. The integration circuit 102 of the sigma modulation circuit 100 includes three feedback circuits m111
To m113. The feedback circuit m111 outputs the output of the third-stage integrator m103 to the second-stage integrator m1.
02, and the feedback circuits m112 and m1
13 is a fifth and seventh stage integrators m105 and m10
7 is output to the integrators m104 and m of the fourth and sixth stages.
Negative feedback is provided to the input side of 106.

These feedback circuits m111 to m113 form three partial negative feedback loops, and the quantization noise level of the 1-bit digital signal is centered on a frequency (zero frequency) corresponding to the gain of each partial negative feedback loop. And drops sharply. In the following, a portion of the frequency characteristic of the quantization noise whose level is reduced is referred to as a dip.
By these dips, high-frequency quantization noise is suppressed, and the level of the quantization noise can be kept at a predetermined value or less up to the upper limit of a desired use frequency band, for example, 20 kHz.

In the delta-sigma modulation circuit 100, after the audio signal is modulated into a 1-bit digital signal, the 1-bit digital signal is transmitted to a receiving or reproducing device (not shown) by, for example, a low-order low-pass filter. Demodulated to an analog sound signal.

[0009]

In the transmission of digital signals, for example, a main signal such as an acoustic signal and
For example, it may be required to simultaneously transmit both a sub signal such as a flag indicating channel information and the like. However, since the 1-bit digital signal transmitted by the 1-bit digital encoding method is a continuous data sequence in the time axis method, the main signal and the sub-signal can be transmitted without impairing the advantage that demodulation is easy. Are difficult to transmit.

In the conventional multi-bit encoding method, when transmitting both the main signal and the sub-signal, the main signal and the sub-signal are transmitted in a time-divided manner. Here, in the multi-bit encoding method, when the encoded data string is returned to an analog signal, word synchronization is required. Therefore, the modulation circuit modulates the main signal and the sub signal in a data format including the main signal and the sub signal in one word, and the demodulation circuit modulates the main signal and the sub signal in accordance with the standardized data format. If the signals are separated, both the main signal and the sub-signal can be transmitted in a time-divided manner.

Here, in the multi-bit encoding method, since word synchronization is essential, signals other than the main signal are transmitted even when the sub signal is not transmitted.
It has a circuit for separating the main signal according to a predetermined data format. Therefore, when transmitting a sub-signal, simply changing the data format of the circuit,
Since a circuit for separating the sub-signal from the main signal and the sub-signal can be configured, it is not necessary to add a new circuit.

On the other hand, in the 1-bit digital encoding system, a data string continuous in the time axis direction is transmitted. Therefore, in order to divide the main signal and the sub-signal in the time axis direction and transmit them, a circuit for separating the main signal and the sub-signal in accordance with the data format standardized at the time of modulation is provided by a demodulation circuit. Needs to be newly added, and the circuit configuration of the demodulation circuit becomes complicated. In addition, once the data format is standardized, it is difficult to change the data format. Therefore, if the data is divided and transmitted in the time axis direction, the advantage of the 1-bit digital encoding method is hindered.

The present invention has been made in view of the above problems, and has as its object to transmit both a main signal and a sub signal without impairing the advantages of the 1-bit digital encoding system. A method for transmitting a signal via a 1-bit digital signal, a delta-sigma modulation circuit, and a demodulation circuit.

[0014]

According to the first aspect of the present invention, there is provided:
In order to solve the above problem, a signal transmission method via a bit digital signal includes a modulation step of modulating a main signal into a 1-bit digital signal by delta-sigma modulation; A method for transmitting a digital signal and a demodulating step of demodulating the transmitted 1-bit digital signal, a method for transmitting a signal via a 1-bit digital signal, wherein the following steps are provided.

That is, the modulating step includes a step of changing the shape of the quantization noise distribution of the main signal based on the sub-signal, and the demodulating step includes a step of quantizing the transmitted 1-bit digital signal. The method is characterized by including a step of extracting a sub-signal based on a shape of a noise distribution.

The shape of the quantization noise distribution of the 1-bit digital signal may be changed, for example, by changing the coefficient of a multiplier provided between cascaded integrators, or changing the loop gain of a partial negative feedback loop. Can be changed.

In the above configuration, the sub signal is added as a shape of the quantization noise distribution of the 1-bit digital signal.
Therefore, the main signal can be demodulated in the same manner as when the sub signal is not added. As a result, both the main signal and the sub-signal can be transmitted by one-channel 1-bit digital signal without obstructing the feature of the delta-sigma modulation that demodulation is easy.

In addition, since the sub-signal is the quantization noise itself of the 1-bit digital signal, in the 1-bit digital signal, the main signal and the sub-signal exist in the same region both in time and frequency. I do. Therefore, it is possible to prevent a third party from removing, changing, and falsifying the sub signal.

According to a second aspect of the present invention, there is provided a delta-sigma modulation circuit for generating a 1-bit digital signal by performing a delta-sigma modulation on a main signal. And a sub-signal adding means for changing the shape of the quantization noise distribution of the 1-bit digital signal according to

In the above configuration, the sub-signal adding means changes the coefficient of the multiplier provided between the cascade-connected integrators or changes the loop gain of the partial negative feedback loop by one bit. The shape of the quantization noise distribution of the digital signal is changed according to the sub-signal.

Therefore, the delta-sigma modulation circuit can easily demodulate the main signal, can transmit the main signal and the sub-signal on a single channel, and can remove, change, and falsify the sub-signal by a third party. , It is possible to generate a 1-bit digital signal which is difficult.

Further, in the delta-sigma modulation circuit according to a third aspect of the present invention, in the configuration of the second aspect, a plurality of input signals serving as main signals are input to the first stage and connected in cascade with each other. An integrator, an adder for adding the outputs of the integrators, and quantizing the output of the adder,
A quantizer for outputting a 1-bit digital signal; and a partial negative feedback circuit forming a partial negative feedback loop by negatively feeding back the output of the integrator to the input side of an integrator preceding the integrator. The sub-signal adding means includes a loop gain changing means for changing a loop gain of the partial negative feedback loop according to the sub-signal.

In the above configuration, the quantization noise level of the 1-bit digital signal generated by the delta-sigma modulation circuit drops sharply around a frequency (zero frequency) corresponding to the loop gain.

When the sub signal changes, the loop gain changing means changes the loop gain of the partial negative feedback loop, for example, by changing the multiplier coefficient of the partial negative feedback circuit. As a result, the quantization noise level of the 1-bit digital signal drops sharply around the zero-point frequency different from that before the change of the sub-signal, and the sub-signal adding means can largely change the shape of the quantization noise distribution. Further, since the zero point frequency is determined by the loop gain, if the loop gain is set to a predetermined value, the quantization noise distribution of the 1-bit digital signal changes to a predetermined shape. As a result, the delta-sigma modulation circuit can generate a 1-bit digital signal that makes it easier to determine the sub-signal on the demodulation side.

In addition, in the delta-sigma modulation circuit according to a fourth aspect of the present invention, in the configuration of the second or third aspect, the main signal is an acoustic signal, and the sub-signal is
It is a signal indicating at least one of channel information, presence / absence of pre-emphasis, a flag for copyright protection, and a mastering code.

In the above configuration, each information serving as a sub signal is information that is closely related to an audio signal serving as a main signal and has a small amount of information. Therefore, even when the sub-signal adding unit cannot change the shape of the quantization noise distribution of the 1-bit digital signal to an excessively large shape, the delta-sigma modulation circuit can add the information as a sub-signal without any problem. . Further, from the 1-bit digital signal generated by the delta-sigma modulation circuit having the above-described configuration, removal of a sub signal,
Since it is difficult to change and falsify, it is possible to surely protect each of the above information that is closely related to the main signal and that is greatly damaged when removal is performed.

On the other hand, a demodulation circuit according to a fifth aspect of the present invention
In order to solve the above problem, in a demodulation circuit for demodulating a 1-bit digital signal generated by delta-sigma modulation of a main signal, a quantization noise distribution of the 1-bit digital signal has a shape according to a sub-signal. A sub-signal discriminating means for discriminating an added sub-signal by comparing the determined shape of the quantization noise distribution stored in advance with the shape of the quantization noise distribution of the received 1-bit digital signal; It is characterized by having.

In the above configuration, when the demodulation circuit receives the 1-bit digital signal, the sub-signal determining means determines the shape of the quantization noise distribution of the 1-bit digital signal and the shape of the quantization noise distribution stored in advance. Compare and extract the sub-signal based on the difference between the two. Thus, the demodulation circuit can correctly extract the sub-signal from the received 1-bit digital signal. Furthermore, by storing the quantization noise distribution shape serving as a comparison reference in a storage medium that cannot be read by a third party, such as an IC (Integrated Circuit), the removal and modification of sub-signals by the third party, and Tampering can be reliably prevented.

The demodulation circuit according to the invention of claim 6 is:
In order to solve the above-mentioned problem, in a demodulation circuit for demodulating a 1-bit digital signal of a plurality of channels generated by performing delta-sigma modulation on a main signal of a plurality of channels,
Among the channels, the shape of the quantization noise distribution of the 1-bit digital signal of at least one specific channel is determined according to the sub-signal, and the quantization noise distribution of the received 1-bit digital signal of the specific channel is determined. Is compared with the shape of the quantization noise distribution of the 1-bit digital signal of the other channel, and a sub-signal discriminating means for discriminating the added sub-signal is provided.

In the above configuration, the demodulation circuit is, for example,
Receives 1-bit digital signals of a plurality of channels such as left and right channels. Here, if the shape of the quantization noise distribution is changed in the 1-bit digital signal of the specific channel, the shape of the quantization noise distribution is different from the shape of the quantization noise distribution of the other channels. The sub signal discriminating means includes a 1-bit digital signal of a specific channel and a 1-bit digital signal of another
The shape of the quantization noise distribution is compared with the bit digital signal, and a sub-signal is extracted based on the difference. Further, unlike the configuration of the fifth aspect of the present invention, since it is not necessary to previously store the shape of the quantization noise distribution, the configuration of the demodulation circuit can be simplified. Thereby, with a relatively simple configuration,
A demodulation circuit capable of correctly extracting a sub-signal from a received 1-bit digital signal can be provided.

Further, in the demodulation circuit according to the present invention, in the configuration according to the fifth or sixth aspect, the sub-signal discriminating means may include a part of the quantization noise distribution of the received 1-bit digital signal. It is characterized in that a sub-signal is determined based on a shape in a predetermined specific frequency band.

The method of limiting to a specific frequency band may be, for example, to extract only a component of a specific frequency band from a received 1-bit digital signal using a band-pass filter or the like, or to perform a Fourier transform. Alternatively, only a component of a specific frequency band may be extracted by using an operation such as the above.

In this configuration, since the frequency band to be compared is limited, the comparison becomes easier as compared with the case where the shape of the quantization noise distribution is compared over all the frequency bands. In particular, as in the configuration of the invention described in claim 5,
The area required for storage can be reduced as compared with a configuration in which the shape of quantization noise serving as a comparison reference is stored in advance.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] An embodiment of the present invention will be described below with reference to FIGS.

That is, the acoustic signal transmitting apparatus according to the present embodiment is an apparatus for transmitting an acoustic signal as a main signal,
As shown in FIG. 2, the left and right channel acoustic signal sources 2R and 2R
A modulator 3 for delta-sigma-modulating the analog or multi-bit acoustic signal output by L into a 1-bit digital signal, and demodulating a 1-bit digital signal received via transmission lines 4R and 4L such as optical fibers. And a demodulation device 5. The modulation device 3 corresponds to a delta-sigma modulation circuit described in the claims, and the demodulation device 5 corresponds to a demodulation circuit.

In the modulation device 3, the audio signal from the audio signal source 2R of the right channel is delta-sigma-modulated by the delta-sigma modulation circuit 31, and sent out to the transmission line 4R as a 1-bit digital signal. On the other hand, in the demodulation device 5, the 1-bit digital signal received from the transmission line 4R is demodulated into an acoustic signal by a demodulation circuit 51R and a low-pass filter (hereinafter abbreviated as LPF) 52R. Similarly, in the left channel, the audio signal from the audio signal source 2L is delta-sigma-modulated by the delta-sigma modulation circuit 32 into a 1-bit digital signal, and then transmitted through the transmission line 4L.
And demodulation circuits 51L and LP of the demodulation device 5
The signal is demodulated into an acoustic signal by F52L. The sound signals of both channels demodulated by the demodulation device 5 are transmitted to an amplifier 6
The sound is converted to sound by left and right channel speakers 7R and 7L via R and 6L. In the following, when referring to each member, if there is no particular distinction between left and right, or when both are collectively referred to, the alphabetic character (R or L) added to the end of the reference numeral is omitted, and for example, an audio signal Reference as source 2.

Further, in the acoustic signal transmitting apparatus 1 according to the present embodiment, in order to accurately discriminate acoustic signals of the left and right channels and to demodulate and output the signals in response to the exchange of the transmission lines 4L and 4R, for example. The 1-bit digital signal output from the device 3 has, as a sub-signal to be added to the main signal, channel information indicating which of the left and right channels the sound signal is on.

More specifically, the modulation device 3 includes one of a delta-sigma modulation circuit 31 for performing delta-sigma modulation of a right-channel audio signal and a delta-sigma modulation circuit 32 for performing delta-sigma modulation of a left-channel audio signal. An additional information signal generating circuit (sub signal adding means) 10 is connected to the delta sigma modulation circuit 31 of one channel (here, the right channel). The shape of the quantization noise distribution of the bit digital signal can be changed.

In the following, for convenience of explanation, an example will be described in which a delta-sigma modulation circuit having an integral order of 7 and three partial negative feedback loops is used. Can be set freely according to.

As shown in FIG. 1, the delta-sigma modulation circuit 31 includes an integration circuit 22 for integrating an analog audio signal input from the audio signal source 2 to the input terminal 21 at a higher order.
, An adder 23 for adding the next-order integrated output, and an adder 2
3 and a digital / analog converter 25 for converting the output of the quantizer 24 into an analog value and feeding it back to the integrating circuit 22. It has.

The quantizer 24 samples the output of the adder 23 at a predetermined sampling frequency FS, and derives an output of “1” when the output is 0 or more, and derives an output of “0” when the output is less than 0. Derive the output. As a result, a 1-bit digital signal of the sampling frequency FS is output from the output terminal 26.

In a 1-bit digital encoding system for sampling a multi-bit digital signal at high speed, a quantizer 2
The sampling frequency FS of 4 is usually set to a predetermined multiple of fs, such as 32 fs or 64 fs, where fs is the sampling frequency of the multi-bit digital signal. Here, as in the case of a compact disc, f
Assuming that s = 44.1 kHz, FS is 1.41 MHz at 32 fs, and 2.82 MH at 64 fs.
z.

On the other hand, the integrating circuit 22 includes cascaded seventh-order integrators m1 to m7, and a feedback resistor provided between the input side of the first-stage integrator m1 and the digital / analog converter 25. r0. The feedback resistor r0 is connected to an inverting input terminal of a differential amplifier a1 described later.

The first-order integrator m1 includes a differential amplifier a1
A capacitor c1 as a time constant element provided between the input and output of the differential amplifier a1, and an input resistor r1 provided between the input of the integrator m1 and the inverting input terminal of the differential amplifier a1. It has. The non-inverting input terminal of the differential amplifier a1 is grounded. The output from the differential amplifier a1 is used as the output of the integrator m1 as an integrator m2 in the next stage.
And the adder 23.

The integrators m2 to m7 of the second and subsequent orders have the same configuration, and the reference numerals of the corresponding parts are the same alphabetical characters with the addition of the subscript corresponding to the order of each of the integrators m2 to m7. Is shown. For example, in the third-order integrator m3, the output of the integrator m2 is input via the input resistor r3, and the output of the differential amplifier a3 is input to the next-stage integrator m4 and the adder 23.

Further, the integration circuit 22 according to the present embodiment forms a partial negative feedback loop and changes a loop gain of the partial negative feedback loop based on an instruction of the additional information signal generation circuit 10. Gain changing circuit (partial negative feedback circuit; loop gain changing means) 11a-1
1c is provided.

More specifically, the loop gain changing circuit 1
1a is provided over the second-order integrator m2 and the third-order integrator m3, and can output the output of the integrator m3 negatively to the input side of the integrator m2. Similarly, a loop gain changing circuit 11b is provided in association with the fourth-order integrator m4 and the fifth-order integrator m5,
A loop gain changing circuit 11c is provided in association with the sixth-order integrator m6 and the seventh-order integrator m7. By these loop gain changing circuits 11a to 11c,
In the integrating circuit 22, three partial negative feedback loops are formed. For example, in a partial negative feedback loop formed by the loop gain changing circuit 11a, the output of the integrator m2 is integrated and inverted by the integrator m3, and after being forward-rotated by the loop gain changing circuit 11a, the integrator m2 Is negatively fed back to the non-inverting input terminal of the differential amplifier a2 provided at

With these three partial negative feedback loops,
As shown in FIG. 3, three dips are formed in the frequency characteristic of the quantization noise level of the 1-bit digital signal. The center frequency (zero frequency) f of the dip is determined by the loop gain Gp of each partial negative feedback loop, and as shown in the following equation (1), f ≒ FS × (Gp) ^1/2 / 2π (1) ). In the above equation (1), FS is the sampling frequency of the delta-sigma modulation circuit 31. As described above, the shape of the quantization noise distribution can be changed by lowering the quantization noise level of the 1-bit digital signal at each zero-point frequency.

The gain Gp of the partial negative feedback loop is determined by the multiplier coefficient of the differential amplifier forming the partial negative feedback loop. For example, the gain Gp of the partial negative feedback loop formed by the loop gain changing circuit 11a is different from the multiplier coefficient of the differential amplifier a2, the multiplier coefficient of the differential amplifier a3, and the difference provided in the loop gain changing circuit 11a. It is determined by the product of a dynamic amplifier a11 (described later) and a multiplier coefficient.

Here, the loop gain changing circuit 11a
Is, for example, as shown in FIG.
One end on the output side is connected to the inverting input terminal of the differential amplifier a11, and an input resistor ri capable of changing a resistance value in accordance with an instruction of the additional information signal generation circuit 10; A feedback resistor rf11 provided therebetween and an output resistor ro having one end connected to the output of the differential amplifier a11.
11 is provided. One end on the input side of the input resistor ri is connected to the input of the loop gain changing circuit 11a, that is, the output of the integrator m3. The other end of the output resistor ro11 is connected to the loop gain changing circuit 11a. The output, that is, the differential amplifier a2 provided in the integrator m2
Connected to the inverting input terminal. Note that the differential amplifier a
Eleven non-inverting input terminals are grounded.

For example, a plurality of input resistors ri1, ri2, and ri3 connected in parallel to each other and individual contacts connected to the input sides of the input resistors ri1 through ri3 are connected to the input resistor section ri to change the loop gain. An input-side switch si having a common contact connected to an input of the circuit 11a, that is, an output of the integrator m3, and input resistors ri1 to ri.
3, each individual contact is connected to the output side of the differential amplifier a.
An output side switch so that a common contact is connected to 11 inverting input terminals is provided. Both switches si · s
“o” operates in conjunction with each other based on a control signal given from the additional information signal generation circuit 10. Thereby, the resistance value of the input resistance section ri is selected to a resistance value according to the instruction of the additional information signal generation circuit 10.

In the above configuration, the additional information signal generation circuit 10
Only needs to control the switches si and so of the loop gain changing circuits 11a to 11c based on the channel information. Therefore, the additional information signal generating circuit 10
There is no need to generate a frequency-modulated signal, an amplitude-modulated signal, or the like, and it can be realized by a relatively simple circuit such as a logic circuit.

Here, the multiplier coefficient of the loop gain changing circuit 11a is determined by the resistance value of the input resistance section ri and the feedback resistance rf1.
It is determined by the resistance value of 1. Therefore, the loop gain changing circuit 11a can change the multiplier coefficient according to the instruction of the additional information signal generating circuit 10, and can change the loop gain Gp of the partial negative feedback loop formed by the loop gain changing circuit 11a. The configuration of the remaining loop gain changing circuits 11b and 11c is the same as the configuration of the loop gain changing circuit 11a, and a description thereof will be omitted.

The shape of the quantization noise distribution of the 1-bit digital signal that can be set by the delta-sigma modulation circuit 31 is determined by the combination of the loop gains of the respective partial negative feedback loops. It is selected so as to satisfy the following conditions. That is, for each quantization noise distribution shape, a shape that can secure the dynamic range of the acoustic signal serving as the main signal and that can be distinguished from each other on the demodulation side is selected.

For example, under the conditions required in the current consumer digital audio equipment, an acoustic signal serving as a main signal has a frequency band of 10 kHz to 20 kHz.
It is required to maintain an S / N of about 90 to 100 dB. Therefore, the gain Gp of each partial negative feedback loop
As shown in FIG. 3, for example, a desired dynamic range (for example, 90 d
(Approximately B).

The acoustic signal transmission device 1 according to the present embodiment comprises:
In order to simplify the configuration for adding the channel information, the channel information is added only to the 1-bit digital signal of the right channel, and is not added to the 1-bit digital signal of the left channel. That is, the delta-sigma modulation circuit 3 of the left channel
Reference numeral 2 denotes delta-sigma modulation of the analog audio signal from the audio signal source 2L. Specifically, as shown in FIG. 5, the delta-sigma modulation circuit 32 is a loop gain changing circuit 1 of the delta-sigma modulation circuit 31 shown in FIG.
Feedback circuits m11 to m13 are provided instead of 1a to 11c. Each of the feedback circuits m11 to m13 has a constant gain irrespective of the instruction of the additional information signal generating circuit 10, except that the gain is constant.
It has the same configuration as a. Specifically, for example, a feedback circuit m
In the following, the input of the feedback circuit m11 is
The input resistor ri11 is connected to the inverting input terminal of the differential amplifier a11. Accordingly, in the delta-sigma modulation circuit 32, the loop gain of each partial negative feedback loop becomes constant regardless of the channel information. Therefore, the delta-sigma modulation circuit 32 outputs a 1-bit digital signal in which the shape of the quantization noise distribution is constant. Since the remaining members are the same as those of the loop gain changing circuit 11a, members having the same functions are denoted by the same reference numerals and description thereof is omitted.

Thus, in the modulation device 3 shown in FIG. 2, the delta-sigma modulation circuit 31 performs delta-sigma modulation on the audio signal output from the audio signal source 2R and changes the shape of the quantization noise distribution. , Channel information indicating the right channel is added. As a result, the 1-bit digital signal to which the channel information has been added is output from the output terminal of the right channel. These 1-bit digital signals of the left and right channels are transmitted to the demodulation device 5 via the transmission lines 4R and 4L. In the present embodiment,
No channel information is added to the 1-bit digital signal output from the output terminal on the left channel side.

On the other hand, the demodulation device 5 includes demodulation circuits 51R and 51L and LPFs 52R and 52 for demodulating 1-bit digital signals of left and right channels into analog audio signals.
L and a channel switching circuit 53 for selecting whether or not to switch the left and right channels when outputting demodulated audio signals to the left and right channel amplifiers 6R and 6L.

Each of the demodulation circuits 51 is realized by, for example, a low-pass filter. In this case, the cutoff frequency of the low-pass filter is set to the upper limit frequency Ft of the transmission band that can be transmitted by a 1-bit digital signal. Thereby, the 1-bit digital signal is modulated into an analog signal. The low-pass filter 52 only needs to be able to remove noise components higher than the effective frequency band of the audio signal. Thus, in particular, rather than higher order filters, 1
The following filter is sufficient. This case can be realized, for example, with one resistor and one capacitor.

The cut-off frequency of each low-pass filter 52 arranged at the subsequent stage of each demodulation circuit 51 is set to the upper limit frequency Fa of a band (audible band) for transmitting an audio signal in the transmission band. As a result, in each low-pass filter 52, an audio signal serving as a main signal is extracted from the analog signal, and input to the channel switching circuit 53.

Here, in the high-speed sampling 1-bit encoding method, if the sampling frequency is FS, FS /
It is known that 2 becomes the upper limit frequency Ft of the transmission band, and FS / 6 becomes the upper limit frequency Fa of the frequency band usable as the acoustic band.

For example, assuming that FS = 32 fs and fs is 44.1 kHz as in the case of a compact disc, Ft = 32 × 44.1 / 2 = 705.6 [kHz] (2) Fa = 32 × 44 .1 / 6 = 235.2 [kHz] (3)

However, when the circuit is actually implemented by hardware, it is difficult to sufficiently reduce the quantization noise in the frequency band up to the upper limit frequencies Ft and Fa. Therefore, the S / N condition required for current consumer digital audio equipment, that is, 10 to 20 k
The upper limit frequencies Ft and Ft are set so that the S / N in Hz can be relatively easily set to about 90 to 100 dB.
The realistic value of a is about 1/2 to 1/4 of them. Specifically, for example, Fa is set to about 50 kHz, and Ft is set to about 120 kHz. When the sampling frequency FS is increased to 64 fs, each of the upper limit frequencies Fa and Ft becomes 100 kHz.
z, about 240 kHz.

The channel switching circuit 53
For example, it is realized by a relay or an analog switch.
Switches s1 and s2 for selecting one of two outputs and outputting one of the two inputs are provided. Switch s
One common contact is connected to the LPF 52R, and the common contact of the switch s2 is connected to the LPF 52L. The one individual contact of the switch s1 and the one individual contact of the switch s2 are shared by the right channel amplifier 6
It is connected to the speaker 7R via R. Similarly, the remaining individual contacts of both switches s1 and s2 are commonly connected to a speaker 7L via an amplifier 6L of the left channel. The switches s1 and s2 are switched in conjunction with each other in accordance with an instruction from a channel determination circuit 61 described later. Thus, when outputting the audio signal to the amplifiers 6R and 6L of both channels, the demodulation device 5 can select whether or not to switch the left and right channels.

Further, the demodulation device 5 according to the present embodiment is connected to the outputs of the demodulation circuits 51R and 51L of each channel and, based on the channel information added to the 1-bit digital signal of the corresponding channel, Channel discriminating circuits (sub-signal discriminating means) 61R and 61L for controlling the switching circuit 53 are provided. Each of the channel discriminating circuits 61 extracts the added channel information based on the shape of the quantization noise distribution of the 1-bit digital signal, and switches the left and right channels to the channel switching circuit 53 when the channel information is different from normal. Can be instructed.

Each channel discriminating circuit 61 according to the present embodiment
Stores in advance the shape of the quantization noise distribution serving as a determination criterion, and compares the shape of the quantization noise distribution of the received 1-bit digital signal with the stored shape using, for example, Fourier transform. The channel information added to the 1-bit digital signal is determined based on the difference between the two shapes.

For example, when the sub-signal is not added, that is, when the shape of the quantization noise distribution of the 1-bit digital signal indicating the left channel is stored in each of the channel discriminating circuits 61 as a criterion, Each channel discriminating circuit 61 judges that the received 1-bit digital signal is the left channel when the difference between the two shapes does not exceed a certain value. On the other hand, if a difference is found,
Each channel determination circuit 61 determines that the channel information added to the one-bit digital signal indicates the right channel.

In the above configuration, the operation of the entire acoustic signal transmitting apparatus 1 when both the acoustic signal as the main signal and the channel information as the sub-signal are transmitted simultaneously will be described as follows.

That is, in the modulation device 3, the left channel delta-sigma modulation circuit 32 has a predetermined quantization noise distribution, for example, as shown by a solid line in FIG. It outputs a 1-bit digital signal having a shape. On the other hand, when the 1-bit digital signal transmitted by the acoustic signal transmission device 1 is a stereo signal, the additional information signal generation circuit 10 adjusts the right channel so as to change the shape of the quantization noise distribution of the 1-bit digital signal. To the delta-sigma modulation circuit 31. As a result, the delta-sigma modulation circuit 31 outputs a 1-bit digital signal having a quantization noise distribution shape different from that of the left channel, as indicated by the broken line in FIG.

On the other hand, when the 1-bit digital signal of the correct channel is input to the demodulator 5, the 1-bit digital signal of the right channel is supplied to the channel discrimination circuit 61R.
That is, the 1-bit digital signal whose quantization noise distribution is changed in shape by the additional information signal generation circuit 10 is input, and the 1-bit digital signal of the left channel is input to the channel discrimination circuit 61L.

Therefore, the channel discriminating circuit 61R
Since there is a difference between the shape of the quantization noise distribution of the received 1-bit digital signal and the shape stored in advance, it is determined that the 1-bit digital signal is the right channel, that is, the correct channel. Similarly, the channel discrimination circuit 61L determines that the received 1-bit digital signal has no more than a certain difference between the shape of the quantization noise distribution of the received 1-bit digital signal and the previously stored shape. The left channel, that is, the correct channel is determined. Therefore, both channel discriminating circuit 6
The 1R / 61L instructs the channel switching circuit 53 not to switch the left and right channels.

As a result, the right channel demodulation circuit 51R
The sound signal demodulated by the LPF 52R is output to the right-channel amplifier 6R, and is sounded by the speaker 7R. Similarly, the left channel demodulation circuit 51L / LPF5
The acoustic signal demodulated by the 2L is transmitted to the speaker 7L via the amplifier 6L on the left channel and is converted into an acoustic signal.

On the other hand, for example, the transmission lines 4R and 4L
When a 1-bit digital signal of an unusual channel is input to the demodulation device 5 due to, for example, replacement of the left channel, the 1-bit digital signal of the left channel is input to the channel determination circuit 61R, and the channel determination circuit 61L is Is a 1-bit digital signal of the right channel, that is, a 1-bit digital signal in which the shape of the quantization noise distribution is changed by the additional information signal generation circuit 10.

In this state, the channel discriminating circuit 61R
Indicates that since the difference between the shape of the quantization noise distribution of the received 1-bit digital signal and the shape stored in advance is not more than a certain value, the 1-bit digital signal is the left channel, that is, the wrong channel. Is determined.
Similarly, the channel discrimination circuit 61L recognizes a certain or more difference between the shape of the quantization noise distribution of the received 1-bit digital signal and the shape stored in advance,
The 1-bit digital signal is the right channel, that is,
It is determined that the channel is wrong. Therefore, both channel discriminating circuits 61R and 61L instruct channel switching circuit 53 to switch the left and right channels.

As a result, the right channel demodulation circuit 51R
The sound signal demodulated by the LPF 52R is output to the amplifier 6L on the left channel, and is sounded by the speaker 7L. Similarly, the left channel demodulation circuit 51L / LPF5
The acoustic signal demodulated by the 2L is transmitted to the speaker 7R via the right channel amplifier 6R and is converted into an acoustic signal. Accordingly, even when a 1-bit digital signal of an unusual channel is input to the demodulation device 5 due to the exchange of the transmission paths 4R and 4L, the demodulation device 5 outputs the respective 1-bit digital signals. The channel of the 1-bit digital signal is determined from the shape of the quantization noise distribution, and the sound signal of the correct channel can be output to the amplifiers 6R and 6L of each channel.

Here, the channel information is added to the 1-bit digital signal as the shape of the quantization noise distribution. Further, regardless of which channel information is added, the quantization noise distribution of the 1-bit digital signal is selected so as to secure the dynamic range of the audio signal serving as the main signal. Therefore, the demodulation circuits 51 and LPFs 52 of each channel operate at 1
A bit digital signal can be demodulated into an audio signal.

As described above, in the acoustic signal transmission device 1 according to the present embodiment, in the analog / digital conversion, by using the unavoidable quantization noise distribution as the sub-signal, for example, a simple low-pass filter or the like can be used. The main signal and the sub-signal can be transmitted at the same time without impairing the advantage of the 1-bit digital encoding system that the main signal can be demodulated by the circuit.

Further, by selecting a loop gain so that the quantization noise distribution does not affect the main signal, even if the reproduction is performed by a demodulator that does not support the sub signal, the reproduction can be performed without the influence of the sub signal. It can be carried out. Furthermore, the main signal and the sub-signal are in the time direction and the frequency direction,
The simultaneous presence makes separation difficult, and it is also difficult for a third party to remove, change, and falsify the sub-signal.

The channel discriminating circuits 61R and 61L according to the present embodiment store the shape of the quantization noise distribution when no sub-signal is added as a criterion, but the present invention is not limited to this. . For example, the shape of the quantization noise distribution of the 1-bit digital signal of the right channel to which the sub-signal is added, or an intermediate value between the shapes of the quantization noise distribution of the 1-bit digital signals of the left and right channels may be used. . The same effects as those of the present embodiment can be obtained as long as the shape can determine which channel the 1-bit digital signal is based on the shape of the quantization noise distribution of the received 1-bit digital signal.

The channel discriminating circuits 61R and 61
L is, for example, by extracting each frequency component of the quantization noise distribution using Fourier transform or the like, and converting the shape of the quantization noise distribution of the received 1-bit digital signal and the shape of the stored quantization noise distribution to the frequency. Although the comparison is made for each component, the present invention is not limited to this. For example, a predetermined calculation such as a weighted average may be performed on each frequency component of the quantization noise distribution of the 1-bit digital signal, and the calculation results may be compared. In this case, the result of performing the same operation on the shape of the quantization noise serving as the comparison reference may be stored. Further, the frequency components may not be extracted by calculation such as Fourier transform, but may be compared using a filter or the like. In any case, various comparison methods can be applied as long as channel information can be extracted by comparing the shape of the quantization noise distribution in the received 1-bit digital signal with the stored shape.

Further, when it is difficult to compare the shape of the quantization noise distribution of the 1-bit digital signal due to the fluctuation of the level of the main signal, the quantization noise distribution may be, for example, a period in which the level of the main signal is below a predetermined level. Is detected, and the demodulation device 5 compares the shape of the quantization noise distribution in the period, whereby the extraction accuracy of the channel information can be improved.

[Second Embodiment] The channel discriminating circuit 61 according to the first embodiment previously stores the shape of the quantization noise distribution serving as the comparison reference, and compares the received shape with the received shape. The channel information added to the bit digital signal is determined.

On the other hand, in the present embodiment, a case will be described in which channel information is determined by comparing quantization noise distributions in received 1-bit digital signals of a plurality of channels. As shown in FIG. 6, the acoustic signal transmission device 1a according to the present embodiment has the first configuration except that a channel determination circuit 61a is provided instead of the channel determination circuits 61R and 61L shown in FIG. This is the same as the embodiment. Therefore, members having the same functions as in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The channel discriminating circuit 61a according to the present embodiment
Is connected to the outputs of the demodulation circuits 51R and 51L, and can control the channel switching circuit 53 based on the comparison result of both outputs. Specifically, the channel determination circuit 6
1a compares the two outputs and determines whether the channel is a left channel or a right channel from the difference in the quantization noise distribution between the two outputs. As a result of the determination, when it is determined that the left and right channels are exchanged, the channel switching circuit 53 is instructed to exchange the left and right channels and output the result.

Thus, the demodulation device 5 according to the present embodiment
“a” can extract the sub-signal based on the shape of the quantization noise distribution of the 1-bit digital signal. As a result, the acoustic signal transmission device 1a can simultaneously transmit the main signal and the sub-signal, similarly to the acoustic signal transmission device 1 according to the first embodiment.

Further, the channel discriminating circuit 61a according to the present embodiment extracts a sub-signal by comparing the shape of the quantization noise distribution between the 1-bit digital signals of a plurality of channels. Therefore, unlike each channel discriminating circuit 61 according to the first embodiment, a sub-signal can be extracted without storing a shape serving as a comparison reference. As a result, the storage area can be reduced and the circuit configuration can be simplified as compared with the channel determination circuit 61.

Note that the modulation device 3 according to the present embodiment, based on the channel information,
Although the shape of the quantization noise distribution of the 1-bit digital signal is changed, the present invention is not limited to this, and the quantization noise distribution shapes of both channels may be changed. In this case, by changing the shape of the quantization noise distribution of one channel so that the difference from the shape of the other channel becomes large, compared to the case where the shape of the quantization noise distribution of one channel is fixed, both channels are changed. Can be enlarged. In either case,
On the demodulation device 5a side, if channel information can be extracted by comparing the quantization noise distribution shapes of both channels, substantially the same effects as in the present embodiment can be obtained.

[Third Embodiment] In the first and second embodiments, each of the channel discriminating circuits 61R, 61L, 6
1a compares the shape of the quantization noise distribution over the entire frequency band output from the demodulation circuits 51R and 51L, and thus the comparison procedure may be complicated. In some cases, each channel discriminating circuit is required.

On the other hand, in the acoustic signal transmission apparatus according to the present embodiment, a case where each channel discriminating circuit compares the quantization noise distribution in a predetermined restricted section will be described. Note that the configuration can be applied to both the first and second embodiments. Hereinafter, the case where the configuration is applied to the second embodiment will be described with reference to FIG.

That is, in the acoustic signal transmitting apparatus 1b according to the present embodiment, the channel discriminating circuit 61b provided in place of the channel discriminating circuit 61a, and the demodulating circuits 51R and 51R
A band-pass filter (hereinafter referred to as “1L output”)
62R and 62L). The center frequency of the BPF 62R / 62L is
For example, the frequency is set to be easy to distinguish the shape of the quantization noise distribution indicating each channel information, such as the quantization noise distribution shape dip shown in FIG. Further, the channel determination circuit 61b compares the outputs of the BPFs 62R and 62L to extract channel information.

In this configuration, the band to be compared by the channel discriminating circuit 61b is a predetermined BPF 62R.
It is limited to a 62L passband. Therefore, the comparison procedure can be simplified as compared with the case where the comparison is made over the entire frequency band output by the demodulation circuits 51R and 51L. For example, if the band to be compared is sufficiently narrow, channel information can be extracted only by comparing the levels of the quantization noise distribution in the band with the left and right channels.

When applied to the first embodiment, each of the channel discriminating circuits 61R and 61L
The channel information is extracted by comparing the output of the 2R / 62L with a predetermined value stored in advance.

In the above description, the BPF62R-6
A predetermined range is extracted from the quantization noise distribution by 2L. However, the present invention is not limited to this. For example, in a Fourier transform, a frequency band to be calculated is limited, and used when comparing the quantization noise distribution. May be limited.

As described above, the acoustic signal transmission devices 1.1, 1a, and 1b according to the first to third embodiments perform the delta-sigma modulation of the main signal to modulate the main signal into a 1-bit digital signal; 1 through the path or the recording medium.
Transmitting a bit digital signal;
An apparatus for transmitting a main signal and a sub-signal using a signal transmission method via a 1-bit digital signal having a demodulation step of demodulating a bit digital signal. And changing the shape of the quantization noise distribution of the main signal, and extracting the sub-signal upon demodulation based on the shape of the transmitted quantization noise distribution of the 1-bit digital signal. .

In the above configuration, the sub signal is added as the shape of the quantization noise distribution of the 1-bit digital signal.
Therefore, the main signal can be demodulated in the same manner as when the sub signal is not added. As a result, both the main signal and the sub-signal can be transmitted by one-channel 1-bit digital signal without obstructing the feature of the delta-sigma modulation that demodulation is easy.

In addition, since the sub-signal is the quantization noise itself of the 1-bit digital signal, in the 1-bit digital signal, the main signal and the sub-signal exist in the same area both in terms of time and frequency. I do. Therefore, it is possible to prevent a third party from removing, changing, and falsifying the sub signal.

In the first to third embodiments, the shape of the quantization noise distribution of the 1-bit digital signal is changed by changing the loop gain of the partial negative feedback loop in the delta-sigma modulation circuit 31. But it is not limited to this. For example, each order integrator m
The shape of the quantization noise distribution may be changed by changing the multiplier coefficients of the differential amplifiers a1 to a7 (see FIG. 1) provided in 1 to m7. In any case, if the shape of the quantization noise distribution of the 1-bit digital signal can be selected based on the sub-signal, substantially the same effects as in the present embodiment can be obtained.

However, in a delta-sigma modulation circuit having a partial negative feedback loop, the frequency at which the dip is formed (zero frequency) is changed by the loop gain of the partial negative feedback loop. As described above, the quantization noise level of the 1-bit digital signal drops sharply near the zero-point frequency. Therefore, when the loop gain of the partial negative feedback loop is changed to change the zero-point frequency, the loop gain is changed. The shape of the quantization noise distribution changes significantly as compared with the case where it is not changed.

Therefore, as shown in the first to third embodiments, each of the loop gain changing circuits 11a to 11c of the delta-sigma modulation circuit 31 performs the partial negative feedback loop according to the instruction of the additional information signal generation circuit 10. , The modulation device 3 can generate a 1-bit digital signal in which the shape of the quantization noise distribution can be easily determined on the demodulation side.

In the configuration shown in FIG. 4, in order to simplify the circuit, only the resistance value of the input resistance section ri is changed to change the gain of each loop gain changing circuit 11. Although explained, it is not limited to this.
If the configuration is such that the gain of each loop gain changing circuit 11 can be changed according to the instruction of the additional information signal generating circuit 10,
The same effects as in the present embodiment can be obtained. Further, for example,
As shown in FIG. 1, the loop gain of the partial negative feedback loop may be changed by changing the multiplier coefficients of the differential amplifiers a1 to a7 provided in the respective integrators m1 to m7. If the configuration is such that the loop gain of the partial negative feedback loop can be changed in accordance with the instruction of the additional information signal generation circuit 10, the same effect as that of the present embodiment can be obtained.

By the way, in the first to third embodiments, the case where the sub signal added to the main signal is the channel information has been described, but the present invention is not limited to this. For example,
Pre-emphasis, flag for copyright protection,
Alternatively, it may be a mastering code or the like. Since such information has a small amount of information, in order to secure a sufficient dynamic range of the main signal, even if the shape of the quantization noise distribution cannot be set too much, it can be added as a sub-signal without any problem. . In addition, since these pieces of information are closely related to the main signal, they are greatly damaged if they are removed, changed, or tampered by a third party. However, using the 1-bit digital signal transmission method according to each of the above embodiments, a third party can remove the sub-signal,
Since it becomes difficult to change and falsify, such information can be surely protected, which is extremely effective. In any case, the same effect can be obtained as long as the sub-signal is closely related to the main signal and has a small amount of information.

In the first to third embodiments, the case where 1-bit digital signals of two channels on the left and right are transmitted is described as an example. However, the present invention is not limited to this. For example, the present invention can be applied to a case where two or more multi-channel 1-bit digital signals are transmitted. Furthermore, the first
As in the third and third embodiments, when the shape of the quantization noise distribution to be compared is stored in the sub-signal discriminating means (channel discriminating circuit), a single-channel 1-bit digital signal is transmitted. Also applicable to cases. In the case of a single channel, since the channel information has no meaning, other information is transmitted as a sub-signal.

In addition, in the first to third embodiments, the case where the channel information indicates the right channel, that is, the case where the sub signal is binary has been described as an example. However, the present invention is not limited to this. Not something. If a quantization noise distribution having a different shape is made to correspond to each sub-signal value, a sub-signal having a plurality of values can be added. For example, each loop gain change circuit 11a to 11c shown in FIG. 1, when each selectable two loop gain, the combination of the loop gain, because the 2 ³ of the quantization noise distribution shape may be selected from among the It is sufficient to select a quantization noise distribution shape that can secure the dynamic range of the main signal and that can be distinguished from each other on the demodulation side.

On the other hand, the demodulation device (5.5b) shown in the first and third embodiments is a demodulation circuit for demodulating a 1-bit digital signal generated by delta-sigma modulation of a main signal. The shape of the quantization noise distribution of the signal is determined according to the sub-signal, and the shape of the quantization noise distribution stored in advance and the shape of the quantization noise distribution of the received 1-bit digital signal are compared. And sub-signal discriminating means (channel discriminating circuits 61R, 61L, 61b) for discriminating the added sub-signal.

In the above configuration, when the demodulation circuit receives the 1-bit digital signal, the sub-signal discriminating means determines the shape of the quantization noise distribution of the 1-bit digital signal and the shape of the quantization noise distribution stored in advance. Compare and extract the sub-signal based on the difference between the two. Thus, the demodulation circuit can correctly extract the sub-signal from the received 1-bit digital signal. Furthermore, by storing the quantization noise distribution shape serving as a comparison reference in a storage medium that cannot be read by a third party, such as an IC (Integrated Circuit), the removal and modification of sub-signals by the third party, and Tampering can be reliably prevented.

The demodulation device 5a according to the second embodiment
Is a demodulation circuit for demodulating a 1-bit digital signal of a plurality of channels generated by delta-sigma modulation of a main signal of the plurality of channels.
The shape of the quantization noise distribution of the 1-bit digital signal of at least one specific channel is determined according to the sub-signal, and the shape of the quantization noise distribution of the received 1-bit digital signal of the specific channel and other shapes are determined. Comparing the shape of the quantization noise distribution of the 1-bit digital signal of the channel,
It is characterized by having a sub signal discriminating means (channel discriminating circuit 61a) for discriminating the added sub signal.

In the above configuration, the demodulation circuit is, for example,
Receives 1-bit digital signals of a plurality of channels such as left and right channels. Here, if the shape of the quantization noise distribution is changed in the 1-bit digital signal of the specific channel, the shape of the quantization noise distribution is different from the shape of the quantization noise distribution of the other channels. The sub signal discriminating means includes a 1-bit digital signal of a specific channel and a 1-bit digital signal of another channel.
The shape of the quantization noise distribution is compared with the bit digital signal, and a sub-signal is extracted based on the difference.

Further, in this configuration, as shown in the channel determination circuits 61R and 61L according to the first embodiment, it is not necessary to previously store the shape of the quantization noise distribution, so that the configuration of the demodulation circuit can be simplified. . Thus, it is possible to provide a demodulation circuit capable of correctly extracting a sub-signal from a received 1-bit digital signal with a relatively simple configuration.

The demodulation device 5b according to the third embodiment
In the above, the sub signal discriminating means (channel discriminating circuit 61)
b) is characterized in that a sub-signal is determined based on a shape in a predetermined specific frequency band in the quantization noise distribution of the received 1-bit digital signal. In addition, as a method of limiting to a specific frequency band, for example, a component of a specific frequency band may be extracted from a received 1-bit digital signal using a band-pass filter or the like, or an operation such as Fourier transform may be performed. May be used to extract only components in a specific frequency band.

In this configuration, since the frequency band to be compared is limited, the comparison is easier than when comparing the shapes of the quantization noise distributions over all the frequency bands. In particular, the area required for storage can be reduced as compared with the case where the configuration of the quantization noise serving as the comparison reference is stored in advance as in the channel determination circuits 61R and 61L according to the first embodiment.

When the sub-signal is multi-valued, if the frequency band to be compared is limited as shown in the third embodiment, it may be difficult to distinguish the shape of each quantization noise distribution. In this case, if a plurality of frequency bands to be extracted are set, for example, by providing a plurality of BPFs, a multi-valued sub-signal can be extracted without any problem.

In the first to third embodiments, the case where the 1-bit digital signal is transmitted via the transmission lines 4R and 4L has been described as an example. However, the present invention is not limited to this. The present invention can be applied, for example, to the case where the modulation device 3 records a 1-bit digital signal on a recording medium and the demodulation device 5 demodulates the 1-bit digital signal from the recording medium. The modulation device 3 performs 1 based on the main signal and the sub signal.
As long as the bit digital signal is generated and the demodulation device 5 obtains the main signal and the sub-signal from the 1-bit digital signal, the same effects as in the above embodiments can be obtained.

[0113]

According to the first aspect of the present invention, there is provided a signal transmission method via a 1-bit digital signal.
The modulation step of generating the bit digital signal includes a step of changing the shape of the quantization noise distribution of the main signal based on the sub signal, and the demodulation step includes the step of changing the quantization noise of the transmitted 1-bit digital signal. This is a configuration including a step of extracting a sub-signal based on the shape of the distribution.

In the above configuration, the sub signal is added as the shape of the quantization noise distribution of the 1-bit digital signal.
Therefore, there is an effect that both the main signal and the sub-signal can be transmitted without obstructing the features of the 1-bit digital encoding method.

In addition, since the sub-signal is the quantization noise itself of the 1-bit digital signal, the main signal and the sub-signal exist in the same region in terms of time and frequency. Therefore, it is possible to prevent a third party from removing, changing, and falsifying the sub-signal.

The delta-sigma modulation circuit according to the second aspect of the present invention performs delta-sigma modulation of the main signal as described above,
The delta-sigma modulation circuit that generates a 1-bit digital signal has a configuration that includes a sub-signal adding unit that changes the shape of the quantization noise distribution of the 1-bit digital signal according to the sub-signal.

Therefore, the delta-sigma modulation circuit can easily demodulate the main signal, can transmit the main signal and the sub-signal on a single channel, and can remove, change, and falsify the sub-signal by a third party. This makes it possible to generate a 1-bit digital signal that is difficult to perform.

According to the delta-sigma modulation circuit according to the third aspect of the present invention, as described above, in the configuration of the second aspect, an input signal serving as a main signal is input to the first stage.
A plurality of integrators connected in cascade with each other, an adder for adding the outputs of the respective integrators, a quantizer for quantizing the output of the adder and outputting a 1-bit digital signal, and the integrator And a partial negative feedback circuit that forms a partial negative feedback loop by negatively feeding back the output of the integrator to the input side of the integrator at a stage preceding the integrator. And a loop gain changing means for changing a loop gain of the partial negative feedback loop.

In the above configuration, since the loop gain is changed according to the sub-signal, the quantization noise level of the 1-bit digital signal drops sharply around the zero-point frequency different from that before the sub-signal changes, and The signal adding means can largely change the shape of the quantization noise distribution. As a result, the delta-sigma modulation circuit has an effect that it is possible to generate a 1-bit digital signal in which the sub-signal can be easily determined on the demodulation side.

According to a delta-sigma modulation circuit according to a fourth aspect of the present invention, as described above, in the configuration of the second or third aspect, the main signal is an acoustic signal, and the sub-signal is channel information. , Pre-emphasis, a copyright protection flag, and a mastering code.

Therefore, there is an effect that the above-mentioned information which is closely related to the main signal and which is greatly damaged when removal is performed can be transmitted while reliably protecting the information.

As described above, the demodulation circuit according to the fifth aspect of the present invention compares the shape of the quantization noise distribution stored in advance with the shape of the quantization noise distribution of the received 1-bit digital signal. This is a configuration including a sub signal discriminating means for discriminating the added sub signal.

In the above configuration, the sub-signal is extracted by comparing the shape of the quantization noise distribution stored in advance with the shape of the quantization noise distribution of the received 1-bit digital signal. Thereby, the demodulation circuit has an effect that the sub-signal can be correctly extracted from the received 1-bit digital signal.

In addition, by storing the quantization noise distribution shape serving as the comparison reference in a storage medium that cannot be read by a third party, it is possible to reliably prevent the removal, alteration and tampering of the sub-signal by the third party. The effect is also achieved.

As described above, the demodulation circuit according to the sixth aspect of the present invention provides the shape of the quantization noise distribution of the received 1-bit digital signal of the specific channel and the distribution of the quantization noise of the 1-bit digital signal of another channel. And a sub-signal discriminating means for discriminating the added sub-signal by comparing the shape with the sub-signal.

In the above configuration, there is no need to previously store the shape of the quantization noise distribution as in the configuration of the fifth aspect of the present invention. Therefore, it is possible to provide a demodulation circuit capable of correctly extracting a sub-signal from a received 1-bit digital signal with a relatively simple configuration.

According to a seventh aspect of the present invention, as described above, the demodulation circuit according to the fifth or sixth aspect of the present invention has the following structure.
The sub-signal discriminating means is configured to discriminate a sub-signal from a quantization noise distribution of the received 1-bit digital signal based on a shape in a predetermined specific frequency band.

In this configuration, since the frequency band to be compared is limited, the effect that the comparison becomes easier as compared with the case where the shape of the quantization noise distribution is compared over all the frequency bands is obtained. Play.

[Brief description of the drawings]

FIG. 1 illustrates one embodiment of the present invention, and is a block diagram illustrating a main configuration of a delta-sigma modulation circuit.

FIG. 2 is a block diagram illustrating a case where a sub-signal is extracted by comparing with a predetermined quantization noise, and is a main configuration of an acoustic signal transmission device including the delta-sigma modulation circuit.

FIG. 3 is a graph showing a distribution state of quantization noise in a 1-bit digital signal output by the delta-sigma modulation circuit.

FIG. 4 is a block diagram showing a configuration example of a loop gain changing circuit in the delta-sigma modulation circuit.

FIG. 5 is a block diagram illustrating a main configuration of a delta-sigma modulation circuit for a channel whose quantization noise distribution shape is not changed according to channel information.

FIG. 6, showing another embodiment of the present invention, is a block diagram illustrating a main configuration of an acoustic signal transmission device in a case where a quantization signal of both channels is compared to extract a sub signal.

FIG. 7 shows still another embodiment of the present invention, in which a main part of an acoustic signal transmission apparatus in the case of extracting a sub-signal by comparing a specific part of the characteristics of quantization noise of both channels. FIG. 3 is a block diagram illustrating a configuration.

FIG. 8 shows a conventional example, and is a block diagram illustrating a main configuration of a delta-sigma modulation circuit.

[Explanation of symbols]

Reference Signs List 3 Modulation device (delta-sigma modulation circuit) 5.5a 5b Demodulation device (demodulation circuit) 10 Additional information signal generation circuit (sub-signal addition means) 11a Loop gain change circuit (partial negative feedback circuit; loop gain change means) 11b Loop Gain changing circuit (partial negative feedback circuit; loop gain changing means) 11c Loop gain changing circuit (partial negative feedback circuit; loop gain changing means) 23 Adder 24 Quantizer 61R / 61L / 61a / 61b Channel discriminating circuit (sub signal Determination means) m1 to m7 integrator

Claims (7)

[Claims] A modulation step of modulating a main signal into a 1-bit digital signal by delta-sigma modulation; a step of transmitting the 1-bit digital signal via a transmission line or a recording medium; A demodulating step of demodulating a signal, wherein the modulating step changes a shape of a quantization noise distribution of the generated 1-bit digital signal according to the sub-signal. Wherein the demodulating step includes the step of extracting a sub-signal based on the shape of the transmitted quantization noise distribution of the 1-bit digital signal. Signal transmission method. 2. A delta-sigma modulation circuit for generating a 1-bit digital signal by delta-sigma-modulating a main signal, wherein a sub-signal addition for changing a shape of a quantization noise distribution of the 1-bit digital signal according to the sub-signal. A delta-sigma modulation circuit comprising means. 3. An input signal serving as a main signal is input to a first stage, a plurality of integrators connected in cascade with each other, an adder for adding an output of each of the integrators, and an output of the adder. A quantizer that quantizes and outputs a 1-bit digital signal; and a negative feedback that forms a partial negative feedback loop by negatively feeding back an output of the integrator to an input side of an integrator preceding the integrator. 3. A delta circuit according to claim 2, further comprising: a loop gain changing means for changing a loop gain of said partial negative feedback loop according to the sub signal. Sigma modulation circuit. 4. The main signal is an audio signal, and the sub signal is a signal indicating at least one of channel information, presence or absence of pre-emphasis, a flag for copyright protection, and a mastering code. 4. The delta-sigma modulation circuit according to claim 2, wherein: 5. A demodulation circuit for demodulating a 1-bit digital signal generated by delta-sigma modulation of a main signal, wherein a shape of a quantization noise distribution of the 1-bit digital signal is determined according to a sub-signal. The shape of the quantization noise distribution stored in advance and the received 1
A demodulation circuit comprising: a sub-signal discriminating means for comparing the shape of a quantization noise distribution of a bit digital signal with a sub-signal to determine an added sub-signal. 6. A demodulation circuit for demodulating a plurality of 1-bit digital signals of a plurality of channels generated by subjecting a plurality of main signals to delta-sigma modulation, wherein a 1-bit digital signal of at least one specific channel among the respective channels is provided. The shape of the quantization noise distribution of the signal is determined according to the sub-signal. The shape of the quantization noise distribution of the received 1-bit digital signal of the specific channel and the quantization of the 1-bit digital signal of the other channel are obtained. A demodulation circuit comprising a sub-signal discriminating means for comparing the shape of a noise distribution and discriminating an added sub-signal. 7. The apparatus according to claim 1, wherein the sub signal discriminating means receives the received 1 signal.
7. The demodulation circuit according to claim 5, wherein a sub-signal is determined based on a shape in a predetermined specific frequency band in a quantization noise distribution of the bit digital signal.