JP2640811B2 - Audio signal recording / reproducing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing method of an audio signal recorded by a digital signal.

B. Summary of the Invention The audio signal is separated into many narrowband frequency channels,
Detect each amplitude (envelope), record / reproduce,
A method of generating a sine wave of the center frequency of each narrow-band filter, controlling the gain with the amplitude of each reproduced channel, and synthesizing the output to obtain an audio signal, characterized by the following features.

(I) A combination of one or more high-frequency oscillators serving as a reference for a sine wave signal group at the time of reproduction, a flip-flop that steps down the output thereof, and a narrow-band filter of the same duplexer used at the time of recording Obtain a square wave fundamental.

(Ii) When synthesizing an audio signal at the time of reproduction, not only the product (gain control) of the envelope of each narrow-band channel and its center frequency is taken, but also the signal components of the channels near each channel have an appropriate ratio ( The ratio with respect to the center frequency component is positive or negative) to suppress the unnaturalness of the reproduced signal from being perceived.

C. Prior Art Audio signal recording / reproducing methods are roughly classified into analog recording and digital recording. The former has the disadvantage that the signal is degraded when recording / reproducing is repeated, and the latter is disadvantageous in that the signal is less likely to be degraded even if recording / reproducing is repeated, but the recording frequency band must be widened. There is.

D. Problems to be Solved by the Invention It is an object of the present invention to provide a recording / reproducing method of an audio signal in which a band is narrowed in a method of recording with a digital signal and the naturalness of reproduced sound is not impaired. It is.

E. Means for Solving the Problems In order to achieve the above object, an audio signal recording / reproducing method according to the present invention uses a duplexer comprising a narrow band filter of a predetermined number of channels for recording an audio signal to be recorded. Through, the envelope is detected for each channel output of the splitter, each detected output is changed to a time-series signal using an electronic switch, and the signal is passed through an A / D converter,
It is recorded as a digital time-series signal, the output signal of one or more high-frequency oscillators is sequentially down-converted, and a sine wave is formed from each of the down-converted signals. Each of the sine waves is amplified using the gain of each channel determined by the sequence signal, and the sine waves adjacent to each of the sine waves are combined at a predetermined ratio to restore the audio signal. The point is to add sine waves.

F. Function In the audio signal recording / reproducing method of the present invention, the audio signal is band-compressed and digitally recorded, and at the time of reproduction, the oscillation frequency signal is down-converted to obtain each sine wave and record the respective gain. It is controlled by a digital time-series signal.

G. Embodiment The operation principle of the present invention will be described below.

It is said that the human auditory system can receive sounds with a frequency of about 50 Hz to 20 kHz, but it is known that the auditory transmission system consists of a collection of many narrow-band transmission systems. In acoustic psychology, this narrow-band transmission system is called a critical band (hereinafter abbreviated as CB in this specification). The wavelength characteristic of the visual system separates light with three cones of red, green, and blue, and color light with the same output of each cone looks the same color even if the spectral characteristics of longitudinal color light are different. This is the basis of current color photography and color television. The same is conceivable for the auditory system. If the CB shown in FIG. 2 were used, the frequency components f _A and f _B
Is a formula (1).

The output of each channel in FIG. 2 for E _A and E _B is given by equation (2).

It becomes a component of the same CB as E _S of the formula (2) in Figure 2 there are other. For example, in FIG. 2, a composite signal E _S ′ represented by the equation (3) is created by E _C = cos 2πf _C t, E _D = cos 2πf _D t, and E _E = cos 2πf _E t.

E _S '= 0.5E _C + E _D + 0.5E _E (3) E _C = 0.5E ₂ + 1.0E ₃ + 0.5E ₄ E _D = 0.25E ₃ + 0.75E ₄ + 0.75E ₅ + 0.25E ₆ E _E = 0.5E ₅ + 1.0E ₆ + 0.5E ₇ E _S ′ = 0.25E ₂ + 0.75E ₃ + 1.0E ₄ + 1.0E ₅ + 0.75E ₆ + 0.25E ₇ = E _S (4) Equation (2) and From Equation (4), the sound of E _A + E _B and 0.5E _C + E _D
The sound of + 0.5E _E has the same component in CB, and it cannot be distinguished.

If the configuration of the auditory CB is used, it is only necessary to transmit a frequency component that can be heard as an equivalent sound without transmitting the frequency components of the original signal (f _A and f _{B in the} above example). Although the number of auditory CBs is large, in practice octave band
20 to 30 narrow band filter groups can be used.

Next, a description will be given, with reference to FIG. 3, of components that enable band compression of a recording system used in the embodiment of the present invention.

FIG. 3 shows an example of a commercially available duplexer (16 channels) -detector-A / D conversion circuit. When an audio signal is applied to the input, each frequency component can be extracted by a narrow-band filter group (diplexer) 1 of 16 channels of logarithmic frequency having a center frequency of 100 to 5,000 Hz and equally spaced. The output of the duplexer 1 passes through the amplitude detector 2 of each component, and the output of the detector 2 is switched to 16 outputs in time series by the electronic switch 3, and the A / D converter 4 is driven using the clock signal 5. , And output 6 as a digital time-series signal.

FIG. 4 shows waveforms at various points in FIG. FIG. 4 (a) shows N
3 shows the output waveforms of the channel splitter 1 in FIG.
4 (b) shows the output of the detector 2, that is, the detected waveform of FIG. 4 (a). (C) is an output of the detector 2 of the fN _{+ 1} channel, and (d) is an output of the detector 2 of the fN _{+ 2} channel. (E) shows a part of the detection output of (b), (c), (d).

FIG. 1 shows a recording / recording method according to the present invention using the element of FIG.
This is a reproduction system, and 1 to 6 have already been described. The output 6 is applied to a digital recording / reproducing system 7, and the reproduced output is applied to a channel amplitude decoding system 12. The waveforms (b), (c), (d),... Are obtained from the waveform in FIG. On the other hand, the frequency f _S in the high-frequency oscillator 8, 10 Of high frequency. Of course, the frequency ratio of oscillators 8 and 10 is It is not limited to. The outputs of oscillators 8 and 10 are connected to flip-flops 9-1,..., 9-n, 11-1,.
Decrease the frequency by -n. Figure 5 (a) is a waveform of f _S, (b) is the output of the flip-flop 9-1, the frequency is f _S / 2. Similarly, (c) shows the flip-flop 9
The output of -2, (d) is the output of flip-flop 9-3, the frequency ^{_{f S / 2 2, f S}} / 2 3 next respectively, and so forth. Oscillator 10 Is similar, and when they are combined, Is obtained. These square waves are added to each channel of the same duplexer 1 ', 1 "used during recording. That is, the duplexer closest to the center frequency of the square wave of each series of oscillators 8, 10 In addition to the narrow band filter of
Square waves such as (a) to (d) in FIG.
It becomes a sine wave of (d '). By the way, these sine wave signals pass through gain control circuits 13-1 to 13-2n whose gain is controlled by the output waveform of each channel of the channel amplitude restorer 12,
For example, for frequencies f _N to restore the waveform of FIG. 4 (a). The output signals of the gain control circuits 13-1 to 13-2n are added by an adder circuit 14, and a reproduction signal 15 is obtained. Fig. 7 5 shows the center frequency of the duplexer having the frequency ratio shown in FIG.

Figure 8 shows the relationship between the input frequency f _N the reproduction output. If for frequencies f _N of the filter characteristic of (a), (b)
F _N and f _{N + 1,} f _N-1 is the duplexer as - the output of the detector. If the input signal f _N is only to match the frequency of the sequence of FIG. 7, FIG. 8 (b) is a reproduced signal, generally deviates from the sequence of Figure 7. Therefore, the frequency at the time of reproduction (the seventh
The frequency) in view of the series' When viewed _{in, f N 'f N, f} N + 1',
f _N-1 'will be reproduced. 'because it is, FIG. 8 _{(b' f N ≠ f N} ) f N-1 ' from (c' f _{N of) ', f N', f} N + 1 '
In the case of making, as shown in Figs. 8 (c) and (d),
_{f N-2 ', f N} -1', f N ', f N + 1', made on the distribution of f _{N + 2} '. Error on the audibility of the reproduced sound than this it is f _N is played to f _N 'is small.

This circuit is generally a frequency component synthesis circuit shown in Figure No. _{9 (a), 'f N} -1 of the adjacent channel to a channel of' f _N, at a rate of f _{N + 1} 'are k _1, f _N−2 ′ and f _{N + 2} ′ are added at the ratio of k _{2 by} the adder circuit 16 and modulated by the gain control circuits 13-1,..., 13-2n using the output of the channel signal restorer 12. Is done. FIG. 9 (b) is an example of FIG. 8 (b ′) → (c ′) where k ₁ = 0.25 and k ₂ = 0. Note that k ₁ , k ₂ ,...> 0
Not necessarily.

FIG. 10 shows a configuration where k ₁ <0. FIG. 11 shows k ₀ = 1,
FIG. 10A is an example of k ₁ = −0.5, k ₂ = 0.25, and FIG. 10A is an output frequency distribution when a signal of 1.0 is added to f _N ′;
(B) shows a case where f _N of Figure No. 8 (a) is applied to the input, f _N 'is _{0.5, f N-3',} f N-1 ', f N + 1', f N + 3 ′ Is 0.1
With an amplitude of 25 and using k <0, an output close to a single frequency component can be obtained.

H. Effect of the Invention A large band compression effect in the recording / reproducing method of the audio signal,
The envelope of the output of the demultiplexer of the narrow-band multi-channel is recorded, and the envelope is multiplied by the center frequency of each channel at the time of reproduction. Simplifies the whole system. Further, by using not only the center frequency of each channel but also a nearby frequency component with a sine wave to be multiplied by each channel envelope, it is possible to suppress the unnaturalness in the audibility of the reproduced sound.

The present invention can be applied to a multi-track narrow band recording system (analog or digital). The bandwidth of each trunk may be a narrow band, and long-time recording / reproduction is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an audio signal recording / reproducing system according to the present invention, FIG. 2 is a conceptual diagram of a CB, and FIG. 3 shows a configuration of a duplexer-detector-A / D converter. 4 is a block diagram, FIG. 4 is a waveform diagram at various points in FIG. 3, FIG. 5 is an output waveform diagram of an oscillator and a frequency reducer, FIG. 6 is a waveform diagram after passing through a filter corresponding to FIG. Is the distribution diagram of the center frequency of the duplexer, FIG. 8 is a diagram showing the relationship between the frequency input and output, FIG. 9 is a block diagram showing the configuration of the frequency component synthesis circuit, and FIG. 10 is another frequency component. FIG. 11 is a diagram showing a combining circuit, and FIG. 11 is a diagram for explaining an example of combining two different frequency components. 1... Duplexer (logarithmic frequency), 2... Amplitude detector (envelope of each channel), 3... Electronic switch, 4.
.. A / D converter, 5... Clock signal (f _C ), 6... Digital output, 7... Recording / reproduction system, 8, 10... High-frequency oscillator, 9-1 to 9-n; ... 11-n... Flip-flop, 12... Channel amplitude restorer, 13-1,.
…… Gain control circuit, 14 …… Addition circuit, 15 …… Output, 16…
... Addition circuit.

Claims (1)

(57) [Claims] (1) an audio signal to be recorded is passed through a duplexer comprising a narrow band filter of a predetermined number of channels; and (b) an envelope is detected for each channel output of the duplexer. (C) converting each detection output into a time-series signal using an electronic switch; (d) recording the signal as a digital time-series signal through an A / D converter; (e) one or more high-frequency oscillators (F) Form a sine wave from each of the frequency-downgraded signals. (G) Determine the gain of each channel determined by the recorded digital time-series signal. (H) combining the sine waves adjacent to each of the sine waves at a predetermined ratio, and (i) combining the amplified sine waves to restore the audio signal. Recording / reproducing system of the audio signal, characterized in that calculation to.