JPH0789428B2 - Digital recording method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a digital recording system, and more particularly to a digital recording system for recording an analog audio signal as a digital signal on a recording medium.

2. Description of the Related Art Conventionally, in this type of digital recording system, an A / D (analog / digital) converter for digitizing an analog voice signal uses a sampling signal having a frequency that is at least twice the maximum frequency of the analog voice signal. The reality is that the frequency band is quantized and encoded with a fixed number of bits.

In such a conventional digital recording system, in the A / D conversion, since the whole frequency band is quantized by the sampling signal of twice or more the maximum frequency of the analog audio signal and encoded with a constant number of bits, When recording digitized audio information on a recording medium, it is necessary to increase the recording capacity of the recording medium.

This occurs because the storage capacity of the analog audio signal in the recording medium per unit time is proportional to the product of the number of quantized bits and the sampling signal frequency, and it is necessary to reduce the recording capacity.

SUMMARY OF THE INVENTION The present invention has been made in view of such a demand, and an object thereof is to provide a digital recording system capable of improving the recording density by reducing the recording capacity of a recording medium. To do.

According to the digital recording method of the present invention, a first analog-to-digital switch for quantizing an analog voice signal with a sampling signal having a sampling frequency higher than the highest frequency thereof to obtain a first digital signal, Analog voice signal,
A second analog-to-digital converter that quantizes a sampled signal having the same frequency as the sampled signal and a predetermined phase difference into a second digital signal;
Is characterized in that the compression rate of the number of quantization bits in the high frequency part of the digital signal is increased and both digital signals are recorded on the recording medium.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a digital voice recording / reproducing apparatus to which the recording system of the embodiment of the present invention is applied. In the figure,
Sampling signal 10 having a frequency F0 which is more than one times the highest frequency of the analog audio signal to be processed and which has a reference phase φ0
0, the frequency of another sampling signal 101 having the same frequency F0 as the frequency of the sampling signal 100 and being phase-shifted by a predetermined amount with respect to the reference phase φ0, and the frequencies of these sampling signals 100, 101
Another sampled signal 102 having twice the frequency 2F0 with respect to F0
There is provided a sampling frequency generator 1 for generating

The analog audio signal introduced to input terminal 1 is the first A / D
In the converter 3, the sampling signal 10 with the reference phase φ
It is sampled by 0, quantized, and encoded into a digital signal having a predetermined number of bits.

The analog audio signal is also sampled and quantized in the second A / D converter 4 by another phase-shifted sampled signal 101. In this case, the compression unit 5 compresses the number of quantized bits, and as a result, the number of recorded bits is reduced. In this case, 1/2 compression is performed so that, for example, 4-bit encoding is performed with respect to 8-bit encoding, but it is sufficient to perform this compression processing only for high frequency components.

Digital signals from both A / D converters 3 and 4 are temporarily stored in the buffer memory 7. The digital audio signal stored in the buffer memory 7 is recorded in the main storage unit 6 as a recording medium (magnetic tape or the like). At this time, between the digital signals digitized by the A / D converter 3, , The read timing from the buffer memory 7 is controlled so that the digital signals digitized by the A / D converter 4 are interpolated correspondingly.

When the recorded audio signal is reproduced from the main storage unit 6 thus recorded, the temporary digital signal is first stored in the buffer memory 7. Of the digital signals stored in the buffer memory 7, the digital signal which is not bit-compressed at the time of recording (that is, the digital signal by the A / D converter 3) is directly stored in another buffer memory 9, The digital signal being compressed (ie A /
The digital signal from the D converter 4) is stored in the buffer memory 9 via the decompression unit 8.

The both digital data stored in the buffer memory 9 in this way are extracted from the buffer memory 9 so that the bit-compressed and decompressed digital signals are interpolated between the digital signals which are not bit-compressed. The read timing is controlled and read.

The read digital signal is analogized by the D / A (digital / analog) converter 10. At this time, the sampling signal 102 having a frequency of 2F0 generated from the sampling frequency generator 1 is used. It is converted to analog and is output to the output terminal 11 as an analog reproduction signal.

FIG. 2 is a diagram showing an example of a signal level waveform at the time of processing an audio signal in the block of FIG. FIG. 2 (a) shows a waveform when quantized by an analog audio signal and a sampling signal 100 having a reference phase φ0 and a frequency of F0. It shows that sampling is performed at each timing t1, t2, t3, ... Of the sampling frequency F0.

FIG. 2B shows the same analog signal from the reference phase φ0.
This is a waveform when quantized with a sampling signal 101 having a phase φ1 delayed by 180 degrees and a frequency of F0. It indicates that sampling is performed at each timing t1.5, t2.5, t3.5, ... Of the sampling frequency F0.

The quantized data shown in FIG. 2 (b) is bit-compressed by the compression unit 5 in FIG. 1 and encoded to reduce the number of recording bits.
The digital data at time t1.5 shown in (b) is interpolated between the digital data at times t1 and t2 shown in (a),
Further, the digital data at time t2.5 shown in (b) is interpolated between the digital data at times t2 and t3 shown in (a), and the data is sequentially recorded.

Fig. 2 (c) shows the waveform during playback.
D / A conversion processing is performed on the sampled signal 102 having the frequency of. In this case, the bit-compressed digital signal is decompressed and D / A converted by the decompression unit 8 for the opposite operation of the compression unit 5.

Thus, by digitizing an analog audio signal with sampling signals having the same frequency and having a phase difference from each other, one of the digital signals is bit-compressed to reduce the number of recording bits. The amount of recorded information is reduced. In this case, usually, the analog audio signal has a small amount of energy in the high-frequency component compared to the low-frequency component. In particular, the signal does not deteriorate. In addition, distortion components in the high frequency range are D / A converter 1
Since the interpolation filter at 0 can remove to a level that does not usually cause a problem, the frequency characteristic can be kept good without narrowing the dynamic range of the audio signal in practical use.

As described above, according to the present invention, since it becomes possible to perform digital recording by A / D conversion processing at a low sampling frequency which is approximately equal to the highest frequency of the audio signal, it is possible to reduce the amount of recorded information on the recording medium. Therefore, there is an effect that the recording density of the recording medium is improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG.
(C) is a signal waveform diagram for explaining the operation of the block of FIG. 1. Explanation of main part code 1 …… Sampling signal generator 3,4 …… A / D converter 5 …… Compressor 6 …… Main memory

Claims (1)

[Claims] 1. A first analog-to-digital converter for quantizing an analog audio signal with a sampling signal having a sampling frequency higher than the maximum frequency thereof to obtain a first digital signal, and the analog audio signal, A second analog-digital converter that quantizes a sampled signal having the same frequency as the sampled signal and a predetermined phase difference into a second digital signal is provided, and a high frequency band of the second digital signal is provided. A digital recording method characterized in that the compression rate of the number of quantization bits in a portion is increased so that both digital signals are recorded on a recording medium.