JPH09298431A - Variable gain device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sound noise in the case of operation of a variable resistor in any occasion and to ensure the response in the case of the operation of the variable resistor in the variable gain device varying the gain of a reproduction signal through digital signal processing. SOLUTION: The variable gain device is provided with a multiplier means 41 that multiplies a gain coefficient with a controlled signal of a gain change object validating update timing control by zero crossing detection and provides an output, a gain instruction means 10 that instructs a gain of the controlled signal, a zero crossing detection processing means 42 that monitors the amplitude of the controlled signal so as to detect a timing when the waveform of the controlled signal is in crossing with an AC amplitude zero axis, and a coefficient update processing means 43 that updates the multiplication processing coefficient for the multiplier means into a coefficient instructed by the gain instruction means synchronously with the zero cross points of the controlled signal detected by the zero cross detection processing means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain device for varying the gain of a reproduced signal by digital signal processing as a volume function of various audio devices.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a zero-cross detector of an analog electronic volume used in a general gain variable device as a volume function of audio equipment. In FIG. 5, reference numeral 50 is a zero-cross detector that detects a time point when a waveform of a digital audio signal, which is a target of variable gain, crosses an amplitude zero axis as an AC signal. The zero-cross detector 50 includes a DC power supply Vcc and a ground. Zero-crossing detection timer setting resistor R connected in series with
And the middle point of connection of the capacitor C are connected, and an audio signal is further input from the input terminal IN.

In this structure, a resistor R for setting a zero-cross detection timer for preventing abnormal noise from occurring when the gain is changed.
And the capacitor C have a relationship of timer time T = 0.69 × R × C [sec]. For example, when the resistance R is 200 kΩ and the capacitor C is 0.22 μF, the timer time T is 30 ms.

If this is related to the responsiveness of the volume, no matter how quickly the volume is operated, 1
The gain will be updated only once. Further, the lower limit of the frequency of a signal (hereinafter, referred to as a signal) which is a target of the gain change for which the update timing control by the zero cross detection is effective is 167 Hz from the relation of the timer time T = 1 / the zero cross lower limit frequency / 2. .

[0005]

In the conventional gain variable device, the minimum gain update possible time interval and the lower limit frequency of the signal to be received for which the update timing control by the zero-cross detection is effective are made possible by the zero-cross detection timer value of the analog electronic volume. Is decided.

This is because if the zero-crossing detection timer time is shortened and the gain update possible time interval is shortened with emphasis on the responsiveness of the volume, the zero-cross lower limit frequency becomes large, and abnormal noise is generated by the gain update at the time of non-zero-cross. The frequency of generation of abnormal noise due to the gradual amplitude change of the signal) increases.

In FIG. 6, the volume is changed by one step every 5 ms, and the timer time is changed to 2.5 ms (lower limit frequency 20
0 Hz), and shows the relationship of abnormal noise generation at the time of gain update when the signal received is a 20 Hz sine wave. The X mark in the figure is the abnormal sound generation point.

On the other hand, if the sound quality is emphasized and the zero-cross detection timer time is increased so that abnormal noise does not occur even in a low-frequency signal, the gain update possible interval becomes large and the response becomes slow. Especially when high volume operation is performed on the high-frequency signal, the gain change becomes coarse,
Discomfort occurs in hearing.

In FIG. 7, the volume is changed by one step every 5 ms, and the timer time is set to 25 ms (lower limit frequency 200
Hz) and the signal received is a 2 kHz sine wave, the relationship of the gain update is shown, which causes a poor response.

Therefore, the responsiveness and the sound quality (prevention of abnormal noise) are contradictory conditions, and there is the inconvenience that it is necessary to have an auditory evaluation experience to set the zero-cross detection timer of the analog electronic volume.

The present invention has been made in order to solve such a problem, and a gain by digital signal processing capable of preventing abnormal noise from being generated at the time of operating the volume and ensuring responsiveness at the time of operating the volume at any time. An object is to provide a variable device.

[0012]

SUMMARY OF THE INVENTION The present invention is a gain varying device for varying the gain of a reproduced signal by digital signal processing, wherein a gain coefficient is applied to a signal to be changed in gain for which update timing control by zero cross detection is effective. A multiplication means for multiplying and outputting the gain, a gain instructing means for instructing a gain with respect to the signal to be received, and a zero-cross detection for monitoring the amplitude of the signal to detect a timing at which the signal waveform crosses the zero amplitude axis as an AC signal. The processing means and the coefficient updating processing means for updating the multiplication processing coefficient in the multiplying means to the coefficient instructed by the gain instructing means in synchronization with the zero crossing of the received signal detected by the zero crossing detecting processing means.

According to the present invention, it is possible to obtain a variable gain device which can prevent abnormal noise from being generated during volume operation at any time and can secure responsiveness during volume operation.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a gain varying device for varying the gain of a reproduced signal by digital signal processing, and a gain changing for which update timing control by zero cross detection is effective. Multiplier means for multiplying the target signal by a gain coefficient and outputting the result, gain instructing means for instructing the gain for the signal, and the amplitude of the signal being monitored to allow the signal waveform to cross the zero amplitude axis as an AC signal. And a coefficient update processing means for updating the multiplication processing coefficient in the multiplication means to the coefficient instructed by the gain instruction means in synchronism with the zero cross of the received signal detected by the zero-cross detection processing means. The zero-crossing detection processing means monitors the amplitude of the signal-received signal while monitoring the amplitude of the signal-received signal. And the coefficient updating processing means updates the multiplication processing coefficient in the multiplying means to the coefficient instructed by the gain instructing means in synchronism with the zero crossing of the signal received by the zero crossing detecting processing means. When updating, the generation of abnormal noise is prevented and the responsiveness at the time of volume operation is secured.

According to a second aspect of the present invention, in the first aspect of the invention, when a new gain variable from the gain indicating means occurs during the zero cross detection of the zero cross detection processing means, a coefficient corresponding to the gain. Is used for the coefficient update processing, the coefficient corresponding to the latest gain can always be used for the coefficient update processing, and the responsiveness independent of the time-out time of the zero-cross detection processing can be realized.

According to a third aspect of the present invention, in the invention according to the first aspect, when the zero-cross detection processing means cannot detect the zero-cross for a predetermined time or longer, it is forced by a coefficient corresponding to the gain of the gain instruction means. The signal is a DC signal, or an AC amplitude of zero due to the offset of the DC signal component causes a difference from the original zero axis, resulting in zero crossing for a certain period of time or more. Even if it cannot be detected, the coefficient updating process is surely performed, and the generation of abnormal noise can be prevented.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
~ It demonstrates using FIG.

FIG. 1 is a block diagram showing a configuration when a variable gain device according to an embodiment of the present invention is applied to audio equipment. In FIG. 1, reference numeral 1 denotes a sound source that outputs an analog audio signal, which is a low-pass filter (LP
F) The analog audio signal from the sound source 1 that has passed through 2 is converted into a digital signal by the A / D converter 3, and a digital signal processor (hereinafter referred to as DS).
4).

The DSP 4 includes a multiplier 41 for varying the gain of the signal to be received, a zero-cross detection processing section 42 for monitoring the amplitude of the signal to be received and detecting the timing at which the signal waveform crosses the zero amplitude axis as an AC signal. Coefficient update processing unit 43 and coefficient update processing unit 43 that update the coefficient of the multiplication process that determines
An update coefficient storage memory 44 provided therein is provided.

The output terminal of the DSP 4 is connected to a D / A converter 5 for converting the digital signal gain-converted and output from the DSP 4 into an analog signal, which is converted into an analog signal. The audio signal is output to the speaker 8 through the low pass filter (LPF) 6 and the amplifier 7.

Reference numeral 9 is a control unit such as a microcomputer for controlling the DSP 4, and the control unit 9 is connected with a gain indicator 10 corresponding to a volume adjusting key operated by a user.

Next, the operation of the embodiment configured as described above will be described with reference to FIGS.

When the gain instruction information from the gain indicator 10 is input to the control unit 9 in accordance with the user's volume operation, the coefficient calculated by the control unit 9 is stored in the update coefficient storage memory 44 in the coefficient update processing unit 43. It is transferred and stored.

At the same time, the zero-cross detection processing unit 42 starts the zero-cross detection of the signal to be received, and at the time of the zero-cross or the time-out (the elapsed time from the start of the zero-cross detection to the forcible coefficient update processing is called the time-out time, and the corresponding timing is The coefficient corresponding to the multiplier 41 is transferred from the coefficient update processing unit 43 to the multiplier 41 by controlling the coefficient update processing unit 43 in synchronization with a time-out. At this time, even if a new volume operation is performed during the zero-cross detection, the updated coefficient from the control unit 9 is always overwritten in the updated coefficient storage memory 44.

Next, the operation of the zero-cross detection processing section 42 will be described. In the present embodiment, when the amplitude state of the signal to be received satisfies the following expression on the digital signal, it is determined to be at the time of zero cross.

Amplitude value of signal before one sampling × amplitude value of signal of current sampling ≦ 0 In other words, as shown in FIG. 2, it is possible to detect the timing at which the signal waveform crosses the zero amplitude axis.

The time-out time for zero-cross detection is determined by the following formula from the lower limit frequency of the reproduction frequency band.

Time-out time T [s] = 1 / lower limit frequency F [Hz] / 2 ... In other words, it is defined as a zero-cross interval when a sine wave having a lower limit frequency is assumed. In the case of this embodiment, the lower limit frequency F
Is 20 Hz and the timeout time T is 25 ms.

Next, signal processing within one sampling period by the DSP 4 will be described with reference to the flowchart shown in FIG. First, when the gain is updated by the user's volume operation, the control unit 9 determines whether the gain change start flag is set (step S1). Here, when the gain change start flag is set, the gain coefficient transferred from the control unit 9 is stored in the update coefficient storage memory 4
4 and stores it (step S2).

Then, it is determined whether or not the current sampling period is the first sampling period after the start of updating (step S3). If it is the first sampling period, the counter for time measurement is initialized (step S
4) It is detected from the equation whether the signal to be received is a zero cross (step S5). Also, if it is determined in step S3 that the sampling period is not the first one, it is detected whether or not the zero crossing is performed (step S5).

If it is at the time of zero crossing, the gain coefficient stored in the update coefficient storage memory 44 is transferred to the multiplier 41 (step S6). Then, the gain change start flag is cleared (step S7), and then the multiplier 4
At 1, the gain update multiplication process is performed (step S8), and the gain update process is completed.

If it is determined in step S5 that the zero-cross time is not reached, the elapsed time (time-out time) from the start of the zero-cross detection to the forcible coefficient update processing is measured (step S9) to determine whether the next time-out has occurred. It is determined (step S10). Here, if the time is out, the process proceeds to step S6, and if not, the process proceeds to step S8.

In this way, regardless of whether or not the gain is updated,
The signal to be signal is gain-adjusted by the multiplier 41 for each sampling period.

As described above, in the present embodiment, since the DSP for determining the gain is synchronized with the zero crossing of the received signal when the gain is updated, the coefficient updating process of the multiplication process is performed. Since the zero cross of the waveform can be monitored with the time accuracy of the sampling cycle (42.7 kHz, about 22.7 μs), it is generally small during normal voice music reproduction except for special cases such as rectangular wave. That is, as compared with the case where there is no synchronization processing by the zero-cross detection processing, the gain is constantly changed when the amplitude of the signal to be received is sufficiently small, so it is possible to prevent the generation of abnormal noise due to the stepwise amplitude change of the signal to be received. .

Further, the lower limit value of the reproduction frequency band of the signal to be received sets the time (time-out time) from the start of the zero-cross detection, which is a condition of the time management processing in the zero-cross detection processing, to the forced coefficient update processing. This time-out time determines the lower limit frequency of the signal being received for which zero-crossing detection is valid, and at the same time the signal being a DC signal or an AC amplitude zero due to the offset of the DC signal component causes the original zero axis (digital signal Even if the zero cross cannot be detected for a certain period of time or more, a coefficient update process can be forcibly performed. That is, in any case, the gain update processing is surely performed, and malfunctions are prevented.

For example, when the signal to be received is a sine wave and the shadow value in the reproduction frequency band is 20 Hz, a zero cross occurs once every 25 ms. Therefore, if the time-out time is 25 ms, it is possible to always realize the gain update synchronized with the zero-cross for the received signal of 20 Hz or more. This can prevent the generation of abnormal noise.

Further, in the present embodiment, the coefficient corresponding to the latest gain (value associated with the volume operation) can always be used for the coefficient update processing even while the zero-cross detection processing waits for the zero-cross of the signal. Therefore, responsiveness that does not depend on the timeout time of the zero-cross detection process can be realized. That is, it is possible to realize the responsiveness that depends only on the volume operation.

For example, as an example of a series of volume operations by the user, from 0 dB to -20 dB, 1 every 5 ms.
Fig. 4 shows a case of 100 dB attenuation with 1 dB attenuation in steps.
Shown in

In FIG. 4, if the lower limit value of the reproduction frequency band is set to 20 Hz and the timeout time is set to 25 ms, a zero cross is detected every time the volume is attenuated by 5 dB in 5 steps for the signal of 20 Hz, and the coefficient Updates are implemented. That is, the volume is -5, -10, -15, -20 in synchronization with the zero cross every 25 ms.
It changes to dB, no abnormal noise is generated, and the response time is not delayed. In this case, the change is coarser than that of the volume operation, but since it is a low-frequency signal, there is no sense of discomfort in hearing.

Further, for a signal of 2 kHz, a zero cross is frequently detected every 0.25 ms due to a change in the volume, so that the coefficient change is exactly the same as the volume operation, and -1 is synchronized with the zero cross. , -2, ...,-1
It changes to 9, -20 dB. Therefore, no abnormal noise is generated, the response time is not delayed, and the gain change synchronized with the volume operation is obtained.

In this way, the volume operation interval t [s]
In the relationship between the signal frequency f [Hz] and “f <
(T / 2) ”skips a part of the series of volume operations to make the changes coarser, but there is no discomfort in the received signal in the low range compared to the high range, and surely zero cross while ensuring responsiveness. The gain can be updated in synchronization with.

If "f≥ (t / 2)", the gain can be surely updated in synchronization with the zero cross while ensuring the responsiveness without skipping a part of the series of volume operations.

[0043]

According to the present invention, when the gain is updated, the coefficient updating process of the multiplication process is performed by the DSP for determining the gain in synchronization with the zero crossing of the received signal. Thus, it is possible to provide a variable gain device by digital signal processing which can prevent the generation of abnormal noise and can secure the responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram of a variable gain device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram at the time of zero-crossing with respect to a digital audio signal according to the embodiment of the present invention.

FIG. 3 is a flowchart showing a signal processing procedure within one sampling period by the DSP according to the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship of gain update according to the embodiment of the present invention.

FIG. 5 is a block diagram of a zero-cross detector of an analog electronic volume used in a conventional gain variable device.

FIG. 6 is a diagram showing a relationship of conventional gain update for generating abnormal noise.

FIG. 7 is a diagram showing a relationship of conventional gain update in which poor responsiveness is felt.

[Explanation of symbols]

 1 Sound Source 2 LPF 3 A / D Converter 4 DSP 41 Multiplier 42 Zero Cross Detection Processing Section 43 Coefficient Update Processing Section 44 Update Coefficient Storage Memory 5 D / A Converter 6 LPF 7 Amplifier 8 Speaker 9 Control Section 10 Gain Instructing Section

Claims (3)

[Claims] 1. A variable gain device for varying the gain of a reproduced signal by digital signal processing, wherein multiplication is performed by multiplying a gain coefficient of a signal to be changed in gain for which update timing control by zero cross detection is effective, and outputting the multiplied signal. Means, gain instructing means for instructing a gain with respect to the signal to be received, zero-cross detection processing means for monitoring the amplitude of the signal to be detected and detecting a timing at which the signal waveform crosses an amplitude zero axis in an AC signal, Coefficient updating processing means for updating the multiplication processing coefficient in the multiplying means to the coefficient instructed by the gain instructing means in synchronism with the zero crossing of the signal to be detected detected by the zero crossing detecting processing means. Variable gain device. 2. When a new gain variable from the gain instructing means occurs during the zero cross detection of the zero cross detecting processing means, the coefficient corresponding to this gain is used for the coefficient updating processing. The variable gain device according to claim 1. 3. The zero-crossing detection processing means is configured to forcibly update the coefficient with a coefficient corresponding to the gain of the gain instruction means when the zero-crossing detection means cannot detect the zero-crossing for a certain period of time or more. Variable gain device.