JPH0697836A - Acoustic signal transmission method - Google Patents

Abstract

PURPOSE:To compress the quantity of data with the coding of high efficiency and furthermore to transmit the acustic signals with high quality by applying the adaptive quantization processing to both amplitude and phase components respectively. CONSTITUTION:The amplitude component Ai(m) and the phase component thetai(m) are obtained at an orthogonal/polar coordinate transforming part 6 for each discrete frequency in regard of the sequential Fourier transformation frames. A masking processing part 5 calculates a masking curve based on the component Ai(m) and carries out the masking processing to compress the data by an amount equal to the component Ai(m). The component Ai(m) outputted via a changeover switch 9S is supplied to an adaptive quantizing part 23. Meanwhile the component thetai(m) is supplied to a phase estimating part PFC via a latch circuit 10. An adaptive quantizing part 17A refers to a look-up table 39 and applies the adaptive quantization processing to the data on the phase component supplied via a changeover switch 16S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic signal transmitting method for compressing and transmitting an information amount of an acoustic signal.

[0002]

2. Description of the Related Art In recent years, an analog signal is often transmitted (or recorded / reproduced) as a digital signal, for example, a PCM (pulse code modulation) signal.
Since the PCM signal has a large amount of information, a wide transmission band is required for transmitting (or recording / reproducing) the PCM signal. Therefore, in transmission equipment (recording / playback equipment) that performs signal processing of digital signals, and other various equipment,
Conventionally, digital signals have been efficiently processed with a small amount of information. As a high-efficiency coding method capable of efficiently coding a signal with a smaller amount of information, the signal is predicted and only the component (residual component) of the deviation from the predicted value is recorded and transmitted. The various high-efficiency coding schemes described above and some kind of transformation (generally orthogonal transformation) are applied to the signal to extract the characteristics of the signal. The amount of information (bits) per sample (bits) is used by taking advantage of the fact that it is sensitive to changes in small changes, but difficult to detect in areas with large changes in signals even if there is some error. It is well known that various high-efficiency coding schemes and the like for reducing the number have been conventionally proposed.

However, for example, in the well-known high-efficiency coding method configured by applying the linear prediction that is practically used for compressing the amount of information when transmitting a telephone voice signal, the numerator of the prediction system ( Although the zero) and the denominator (pole) are predicted, the predictive ability is not very good, and there is almost no effect on the transmission of the music signal. There are other methods such as the Perco method for performing linear prediction, but this also has a limit in performance. Further, as described above, there has been no prediction method suitable for compressing the information amount related to the transmission (recording) of the music signal. The bit compression method that has been used is to perform bit compression by using a masking effect between adjacent frequencies by, for example, orthogonal transformation. It is cut out as a sequential one frame period in which the joints of the respective successive frames are overlapped with each other and gently connected, and orthogonal transform is performed by Fast Fourier Transform (FFT) for each one of the frames. The masking curve is calculated with respect to the data obtained by the fast Fourier transform of A spectrum that is transmitted (recorded) and has an amplitude smaller than the masking curve is not transmitted (recorded). For example, a spectrum masked by the main spectrum and inaudible does not record or transmit it. . Note that DFT, DCT, or the like can be used as the orthogonal transform.

By the way, the reason why the data of the acoustic signal can be reduced as described above is that, when the sound of a certain frequency component is strongly radiated, it is close to the frequency component as a property of human hearing. This is because the detection capability for the frequency is reduced. Therefore, a small number of bits are assigned to the frequency component of the part where the detection capability is reduced, and the small amplitude signal component is not transmitted at all. Can be realized. Although the signal accuracy is considerably lowered due to the decrease in the amount of data as described above, it is often possible to make it indistinguishable from the case where the original signal is heard by the masking effect of hearing. As described above, conventionally, in order to perform high-efficiency coding, a signal has been predicted or a signal has been orthogonally transformed. However, both the signal prediction technique and the orthogonal transformation technique are used. Even better fusion can be achieved if the fusion is done well so that the orthogonally transformed data of the next frame can be predicted from the orthogonally transformed data, but this has not been done conventionally. It was

In order to solve the above-mentioned problems, the present applicant's company has previously established a predetermined fixed time length according to Japanese Patent Application No. 4-30076, "Method of predicting phase of acoustic signal". The first and second Fourier transform frames in each successive Fourier transform frame cut out from the acoustic signal are discretely Fourier transformed using the same window function, and the first and second Fourier transforms described above are performed. From the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each frame, the phase information for each discrete frequency is obtained for each of the first and second Fourier transform frames described above. A mode of change of the phase information for each identical discrete frequency corresponding to each other in each of the first and second Fourier transform frames is obtained, and a mode of change of the phase information for each discrete frequency described above is obtained. Is constant on the time axis, the predetermined number in the Fourier transform frame of the third time position existing at a time position that is an integer multiple of the time difference between the first time position and the second time position described above. Has proposed a method of predicting the phase information of the Fourier transform frame at the third time position by determining the individual phase information of the discrete frequencies of, and a high efficiency of the acoustic signal by applying the above-mentioned method of predicting the phase information. The coding facilitates the transmission (recording) of acoustic signals and the configuration of the sound source of musical instruments.

FIG. 9 is a block diagram of an encoder that can be used in an application example of the previously proposed method of predicting phase information by the applicant company, and FIG. 10 is a block diagram of a decoder. In FIG. 11, the waveform indicated by AUDIO described in the uppermost part is an acoustic signal targeted for high efficiency encoding, and the acoustic signal is Fr.
As shown by 0, 1, 2, ... Shown in a part of the display of "ame Window", each is cut out so as to have a constant time length, and is made into a sequential Fourier transform frame. Each Fourier transform frame described above is multiplied by a window function so as to have a period having, for example, 1024 sampling points from an acoustic signal, and the joints of successive frames are overlapped with each other to be gently connected. Is cut out as one sequential frame period. The above-mentioned Fourier transform frame for each frame is subjected to orthogonal transform by, for example, discrete finite series Fourier transform (DFT) or fast Fourier transform (FFT). In the following description, the above orthogonal transformation is described as being performed by a fast Fourier transform (FFT).

When the FFT operation is performed on each Fourier transform frame, it is assumed that the number of data (sample number) in each Fourier transform frame is N and the sampling frequency is fs. , F
= Fs / N, the FFT operation result is obtained for each discrete frequency (total N frequencies) for each frequency interval of f, and the FFT operation result is a real number for each discrete frequency. Part (Real) amplitude and imaginary part (Ima
g) amplitude. Using the real part (Real) amplitude and the imaginary part (Imag) amplitude for each discrete frequency described above, the following Equation 1 and Equation 2 are used to perform polar coordinate conversion for each discrete frequency described above. Composite amplitude term (Am
p) and the phase term (Phase). By the way, FF
Of the N real part (Real) amplitudes and the N imaginary part (Imag) amplitudes obtained for each discrete frequency as a result of the T calculation, the N real part (Real) amplitudes have the same value. Two of them appear, and there are N imaginary parts (I
mag) Amplitude, two absolute values have the same value, so the number of valid combined amplitude terms (Amp) is 1/2 of the total number, and the effective phase terms (Phase) terms Since the number is 1/2 of the total number, the number of FFT output data is F
It can be equal to the number of real input data of FT.

[0008]

[Equation 1]

[Equation 2]

Now, for successive Fourier transform frames (frames) that are continuous on the time axis, the real part (Real) amplitude and the imaginary part (Ima) of each discrete frequency.
g) Amplitude and by equation 1 and equation 2, the combined amplitude term (Am
When p) and the phase term (Phase) are obtained, it is natural to predict that two adjacent frames on the time axis will have the same amplitude if the most common sense is taken. Yes, and actually for example the sampling frequency is 44.1K
Assuming that the sample number of 1024 points is set as the frame length (the frame length is about 1/40 second) at Hz, the spectrum obtained by the FFT operation result obtained when the FFT operation is performed on the signal of the piano sound is 1 Comparing 512 amplitudes in one frame with 512 amplitudes in the next frame of that frame, or comparing 512 amplitudes in the next frame of the next frame, in different frames. It is also confirmed that the amount of change between spectra is extremely small.

On the other hand, it may be difficult to predict the phase in successive frames that are continuous on the time axis, because the repetition time of successive frames and the frequency of the signal are irrelevant, and the phase of the signal It is clear from the viewpoint that the frame starts and ends regardless of the above, and it has been conventionally considered difficult to perform signal prediction by orthogonal transform. Then, assuming that the sampling frequency is 44.1 KHz and the number of samples is 1024 points as the frame length,
Looking at the distribution of 512 phases in one frame by the FFT operation result obtained by actually performing FFT operation on the piano sound signal, the distribution of the phases is random. 5 in the frame
It was found that the distribution of 12 phases cannot be predicted.

The above-mentioned proposed inventor Mr. Takahashi of the applicant company predicts the phase information of other frames by using the phase information of one frame in the sequential frames on the time axis. However, for two frames, the manner in which the phase information changes between the phase information for the same predetermined number of discrete frequencies obtained as a result of the Fourier transform for each Fourier transform frame is constant on the time axis. If so, paying attention to the fact that it is possible to predict the phase information of other frames by using the relationship, and as described above, “for two frames, as a result of Fourier transform for each Fourier transform frame, The variation of the phase information between the phase information for each of the same predetermined number of discrete frequencies obtained is constant on the time axis. Establish a bridge hypothesis) and actually use various signals such as single frequency sine wave signal, multiple frequency sine wave signal composite signal, musical instrument (piano) sound signal, etc. After conducting experiments, the phase of the frame predicted according to the above hypothesis and the phase of the actual frame have been correctly predicted to the extent that they are practically agreed, and Takahashi's hypothesis The fact that it holds in practice is supported by various experimental results.

According to Takahashi's hypothesis, data θi (1) of N / 2 phase terms obtained for each discrete frequency in frame 1 shown in FIG. Data θi (2) of N / 2 phase terms obtained for each discrete frequency, and data θi (3) of N / 2 phase terms obtained for each discrete frequency in frame 3, for example. And, for example, the data θi (4) of N / 2 phase terms obtained for each discrete frequency in frame 4, regarding the data of the phase terms at the same frequency value, Data is, for example, θ1
And the phase term data in frame 2 is, for example, θ2, the phase term data in frame 3 is, for example, θ3, and the phase term data in frame 4 is, for example, θ4, θ2
Since the amount of change in phase between frames is almost the same as −θ1≈θ3−θ2≈θ4−θ3≈Δθa, if this hypothesis holds, then for each of the two frames, If the difference in the phase between the data of the phase terms of all the frequency values corresponding to each other in the N / 2 phase terms obtained for each discrete frequency of is different from the above two frames. It is possible to predict the phase of another frame. Specifically, as in the above-mentioned example, the data of the phase term of a certain specific frequency value fa in frame 1 is θ1, and the phase term data in frame 2 is. When the data of the phase term of the specific frequency value fa is θ2, the data of the phase term θ3 of the specific frequency value fa in the frame next to the frame 2 is set to θ3.
≉θ2 + (θ2-θ1) = 2θ2-θ1 (a) is predicted, and the above-described phase prediction is individually performed for all discrete frequencies in frames 1 and 2. By doing so, it is possible to predict the phase of the signal of frame 3.

According to the above-mentioned Takahashi's hypothesis, even if the phase information of one frame, for example, the phase information of only frame 1 is known, it is impossible to predict the phase information of other frames using the phase information. However, if the phase information of two frames is known, it is possible to predict the phase information of another frame, and the phase information of two adjacent frames, for example, the phase information of frame 1 and the phase information of frame 2 , It is possible to predict the phase information of frames other than the above-mentioned two frames, and the distance is K times the time length of one frame.
If the phase information of one frame, for example frame 1 and the phase information of frame 4, is known, the phase information of another frame, for example, frame 7, which is K times the time length of one frame away from frame 4, can be predicted. Generally speaking, the above Takahashi's hypothesis can be expressed as follows: "The first and the first in each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length.
Discrete Fourier transform using the same window function for each second Fourier transform frame, and the same predetermined number of discrete values obtained as a result of the Fourier transform for each of the first and second Fourier transform frames described above. Phase information for each discrete frequency is obtained for each of the first and second Fourier transform frames described above from the data for each frequency, and the phase information for each of the first and second Fourier transform frames described above is obtained. The phase of change of the phase information for each identical discrete frequency is obtained, and it is assumed that the mode of change of the phase information for each discrete frequency is constant on the time axis and the first time position and the The individual phase information of the predetermined number of discrete frequencies in the Fourier transform frame of the third time position existing at the time position that is an integer multiple of the time difference from the second time position is determined, and Fourier It can be to be able to predict the phase information of the conversion frame ".

The block diagram shown in FIG. 9 is an application of the phase prediction technique for acoustic signals based on the Takahashi's hypothesis as described above.
When the information amount of the signal to be recorded and transmitted is compressed and then recorded and transmitted, the amplitude residual signal Ai (m) -Ai (m-1) and the phase residual signal are calculated for each frame. Difference signal Δθi
10 shows an example of the configuration of an encoder configured to record and transmit (m) = θi (m) − {2θi (m−1) −θi (m−2)}, and FIG. Shows a configuration example of the decoder. FIG. 12 is a diagram showing the predicted value of the phase and the residual value in the decoder shown in FIG. Each of the above residual signals becomes zero if the prediction is correct, but usually a slight deviation from the predicted value occurs, so the above residual signals rarely become zero but the original signal The information amount of the residual signal is much smaller than the information amount.

In FIG. 9, reference numeral 1 denotes an input terminal of a digital audio signal to be recorded and transmitted, which is overlapped by a block 2 from the digital audio signal supplied to the input terminal 1 of the digital audio signal. Sequential Fourier transform frames cut out so as to have a predetermined fixed time length in the selected state are multiplied by a window function for each period having, for example, N sampling points, and each successive frame The fast Fourier transform operation (FFT operation) is performed in the block 4 after the window function is multiplied in the block 3 so as to form one sequential frame period in which the joints are overlapped with each other and gently connected. Be done. As a result of the FFT calculation, the same constant frequency interval f {however, 1 for each Fourier transform frame is obtained.
Number of data in Fourier transform frame for each frame The number of samples is N, the sampling frequency is fs, and f = fs /
For each of the N discrete frequencies having N}, the real part (Rea
l) The data of the FFT operation result including the amplitude and the imaginary part (Imag) amplitude is obtained.

As described above, the N discrete frequency data obtained as a result of the FFT operation is subjected to signal processing by different signal processing devices for each discrete frequency data. However, FIG. 9 illustrates only the configuration of one of the N signal processing devices. In FIG. 9, the signal processing device is a component between the block 6 and the multiplexer 18, which is displayed as a rectangular coordinate → polar coordinate conversion.
Data of a specific discrete frequency, which is obtained as a result of the FFT operation and is composed of a real number part and an imaginary number part for each of N discrete frequencies, is polar coordinate-transformed by the orthogonal coordinate → polar coordinate transforming part 6 and becomes an amplitude term. After the separation into the phase term, the calculation of the amplitude according to the above-mentioned Expression 1 and the calculation of the phase according to the above-mentioned Expression 2 are performed, so that the discrete each of the above-described discrete frames is obtained. Composite amplitude term Ai (m) for each frequency
And the phase term θi (m) can be obtained. The composite amplitude term Ai (m) of a specific discrete frequency obtained as the calculation result of the orthogonal coordinate → polar coordinate conversion unit 6 is supplied to the latch circuit 7, the subtractor 8 and the data selector 9. The data selector 9 selects one of the setting data based on the above-described combined amplitude term Ai (m) and the residual data output from the subtracter 8 according to the switching signal supplied to the terminal 34. And outputs it to the multiplexer 18.
The switching operation of the data selector 9 described above is performed in conjunction with the switching operation of the data selector 16 described later.

Further, the Cartesian coordinates → polar coordinates conversion unit 6 described above.
The phase term θi (m) of a specific discrete frequency obtained as the calculation result of is supplied to the latch circuit 10, the subtractor 14, and the data selector 16. The data of the phase θi (m) output from the rectangular coordinate → polar coordinate conversion unit 6 is held in the latch circuit 10 as the calculation result of the phase of a specific discrete frequency (probably fa) in the m-th frame. The phase data held in the latch circuit 10 before the operation, that is, the phase θi output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the m−1th frame. The data of (m-1) is held in the latch circuit 12 in the phase prediction unit PFC. The phase predictor PFC described above includes a latch circuit 12, an amplifier 11 having a gain of 2, and a subtractor 13 in the illustrated configuration example.
It is composed of and. The phase data held in the latch circuit 12 before the data of the phase θi (m-1) is held in the latch circuit 12, that is, the specific discrete frequency fa in the (m-2) th frame. The data of the phase θm−2 output from the Cartesian coordinate → polar coordinate conversion unit 6 as the phase calculation result is supplied to the subtractor 13 as a subtraction signal, and is supplied to the subtractor 13 as a subtraction signal. Since the output from the amplifier 11 having the gain of 2 is supplied, the predicted phase data output from the subtractor 13, that is, the predicted phase data output from the phase prediction unit PFC. Is 2θi
(m-1)-[theta] m-2.

The phase θm of the specific discrete frequency obtained as the calculation result of the Cartesian coordinate → polar coordinate conversion unit 6 is
It is supplied to the latch circuit 10, the subtractor 13, and the data selector 16. Before the data of the phase θm output from the Cartesian coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency (probably fa) in the m-th frame is held in the latch circuit 10. Latch circuit 1
The phase data held at 0, that is, the phase θi (m-1) output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the m-1 th frame. Data is held in the latch circuit 12 in the phase predicting unit PFC configured by the latch circuit 12, the amplifier 11 having a gain of 2, and the subtractor 13. The terminal 5 is a shift clock signal supply terminal. The data of the above-described phase θi (m-1) is the latch circuit 12
Is output from the orthogonal coordinate → polar coordinate conversion unit 6 as the calculation result of the phase data held in the latch circuit 12 before being held in, ie, the phase of the specific discrete frequency fa in the m−2nd frame. Phase θi (m-2)
Data is supplied to the subtractor 13 as a subtraction signal, and the subtraction signal 13 is supplied to the subtractor 13 as a subtracted signal because the output from the amplifier 11 having a gain of 2 is used. , The predicted phase data output from the subtractor 13, that is, the predicted phase data output from the phase prediction unit PFC is 2θi (m−1) −θi (m−
2) {see FIG. 12}.

Predicted phase data 2θi (m-1) -θi (m-2) output from the phase predictor PFC is subtracted from the actual phase data θi (m) by the subtractor 14, , The phase residual signal Δθi (m) = θi (m)-{2θi (m-1) -θi (m-
2)} is output and supplied to the quantizing scaling 17 via the data selector 16, where the quantizing size is set according to the frequency, and then supplied to the multiplexer 18. In the multiplexer 18 described above,
An amplitude residual signal ΔAi (m) of a specific discrete frequency (probably fa now) and a phase residual signal Δθi (m) of a specific discrete frequency fa are combined and supplied to the output terminal 19. To do. It should be noted that the output terminal 19 has at least 1
The degree is the original amplitude component Ai (m) and the phase component θi
(m) Needless to say, it is supplied. The multiplexer 18 includes all other signal processing circuits that generate the amplitude residual signal ΔAi (m) and the phase residual signal Δθi (m) for each predetermined number of discrete frequencies in the Fourier transform frame. Since the output data from is also supplied,
From the multiplexer 18, the data of the acoustic signal in which the information amount is compressed is output and sent to the transmission path via the output terminal 19.

Next, an example of the configuration of the receiving side of the transmission system will be described with reference to FIG. In FIG. 10, reference numeral 20 denotes an input terminal of a decoder provided on the receiving side, and this input terminal 20 receives from the transmitting side described above with reference to FIG. 9 via a transmission line (not shown). The data of the acoustic signal in a state where the amount of information transmitted to the side is compressed, that is,
A demultiplexer (not shown) separates data from an acoustic signal that includes a predetermined number of amplitude residual signals ΔAi (m) for each discrete frequency in the Fourier transform frame and a phase residual signal. In addition, the amplitude residual signal ΔAi (m) and the phase residual signal Δθ for each specific discrete frequency
A signal containing i (m) is provided. The signal including the amplitude residual signal ΔAi (m) and the phase residual signal Δθi (m) supplied to the input terminal 20 for each specific discrete frequency is the data of a specific discrete frequency. Predetermined signal processing is performed by a signal processing device that performs the signal processing of. FIG. 10 typically shows one signal processing device that performs signal processing on data of a specific discrete frequency.

The input terminal 20 includes an original amplitude component Ai (m) of a specific discrete frequency, a phase component θi (m), an amplitude residual signal ΔAi (m) and a phase residual signal Δθi (m). In the signal processing circuit supplied with the signal composed of, the de-multiplexer 21 sets the original amplitude component A of a specific discrete frequency (probably fa).
i (m), phase component θi (m), and amplitude residual signal ΔA
i (m) and the phase residual signal Δθi (m) are separated and supplied to the amplitude component signal processing circuit and the phase component processing circuit. The data given from the latch circuit 24 to the adder 25 in FIG.
Amplitude residual signal ΔAi given to adder 25 from 1
(m) is the amplitude residual signal ΔAi in the m-th frame
In the case of (m), since it is the data Ai (m-1) of the combined amplitude term of the m-1th frame, m in the adder 25.
-Data Ai (m-1) of the composite amplitude term of the -1st frame,
The amplitude residual signal ΔAi (m) in the m-th frame is added, and the adder 25 outputs data Ai (m) of the composite amplitude term of the m-th frame, which is held by the latch circuit 24. Data selector 2
It is supplied to the polar coordinate → rectangular coordinate conversion unit 27 via 6.

Further, as described above, the demultiplexer 2
Specific discrete frequencies separated by 1 (for example, fa
The original amplitude component Ai (m), the phase component θi (m), and the phase component θi (m) and the phase residual in the amplitude residual signal ΔAi (m) and the phase residual signal Δθi (m). The difference signal Δθi (m) is requantized by the requantizer 22 and then supplied to the adder 29 and the data selector 30. The fact that the data output from the adder 29 becomes the data θi (m) of the phase term of a specific discrete frequency in the m-th frame means that the two data added by the adder 29 are , The phase residual signal Δ given to the adder 29 from the demultiplexer 21
θi (m) is the phase residual signal Δ in the m-th frame
θi (m) and 2θi output from the phase prediction unit PFC
This is because (m-1) -θi (m-2). The data θi (m) of the phase term having a specific discrete frequency in the m-th frame output from the adder 29 is supplied to the polar coordinate → rectangular coordinate conversion unit 27 via the data selector 30, and It is supplied to the latch circuit 28. A shift clock signal is supplied to the terminal 23.

The phase θ output from the adder 29 described above.
Before the data of i (m) is held in the latch circuit 28,
The phase data held in the latch circuit 28, that is, the specific discrete frequency f in the (m-1) th frame
The data of the phase θi (m-1) of a is held in the latch circuit 12 in the phase predicting unit PFC configured by the latch circuit 12, the amplifier 11 having a gain of 2, and the subtractor 13. The data of the above phase θi (m-1) is the latch circuit 1.
The data of the phase held in the latch circuit 12 before being held in 2, that is, the data of the phase θi (m-2) of the specific discrete frequency fa in the m-2th frame is subtracted by the subtractor 13 Is supplied as a subtraction signal to the subtractor 13, and the subtracted signal is supplied to the subtractor 13 because the output from the amplifier 11 having a gain of 2 is used. The predicted phase data output, that is, the predicted phase data θi (m) output from the phase prediction unit PFC is 2θi (m−1) −θi.
(m) -2. Therefore, the predicted phase data θi (m) = 2θi (m-1) output from the phase predictor PFC described above.
-Θi (m-2) and the phase residual signal Δθ of the m-th frame
i (m) = θi (m)-{2θi (m-1) -θi (m-2)}
When and are added by the adder 29, the adder 29 outputs the data θi (m) of the phase term of the specific discrete frequency fa in the m-th frame.

M output from the adder 25 as described above
The data Ai (m) of the composite amplitude term of the th frame and the data θi (m) of the phase term of the specific discrete frequency in the mth frame output from the adder 29 are respectively predetermined data selectors. By being supplied to the polar coordinate → rectangular coordinate conversion unit 27 via 26 and 30, the polar coordinate → rectangular coordinate conversion unit 27 causes the data Ai (m) of the composite amplitude term of the m-th frame described above and the adder 29. The data θi (m) of the phase term of the specific discrete frequency in the m-th frame output from the real number part (Real) amplitude and the imaginary part (Imag) at the specific discrete frequency fa described above. The amplitude and the calculated value are output and supplied to the inverse FFT operation unit 31. Since the inverse FFT operation unit 31 is supplied with output data from all the signal processing circuits provided for each predetermined number of discrete frequencies in the Fourier transform frame, the inverse FFT operation unit 31 also outputs the output data. And the audio signal data are restored and subjected to the window function multiplication shown in block 32 and the overlap addition shown in block 33 to be restored to the original digital audio signal. Output terminal 35
Will be sent to.

[0025]

If the acoustic signal transmission (recording and reproduction) is performed by applying the above-mentioned "acoustic signal phase prediction method" proposed by the applicant of the present invention, the acoustic signal will be enhanced. Since it can be efficiently encoded and transmitted (recorded and reproduced), the desired effect can be obtained, but the data amount is compressed by even higher efficiency encoding and the acoustic signal is transmitted in a high quality state. There was a need for a method of transmitting audio signals that could be recorded and played back.

[0026]

SUMMARY OF THE INVENTION The present invention discretely Fourier transforms a signal of each successive Fourier transform frame cut out from an acoustic signal so as to have a predetermined fixed time length by using the same window function. By using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform for each Fourier transform frame, the amplitude component for each discrete frequency obtained for each Fourier transform frame described above. In the transmission method of the acoustic signal which is transmitted after high-efficiency coding of the phase component and the phase component, the masking curve for each Fourier transform frame is calculated from the amplitude component for each discrete frequency obtained for each Fourier transform frame described above. Then, using the masking curve for each Fourier transform frame described above, the data amount of the amplitude component of the corresponding Fourier transform frame is calculated. A means for reducing, and a method of transmitting an acoustic signal, wherein data of the difference in amplitude component of each successive Fourier transform frame whose data amount is compressed as described above is obtained, and adaptive quantization is performed for transmission thereof. And discrete Fourier transform using the same window function on the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length, and for each Fourier transform frame described above. Using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform, the amplitude component and the phase component of each discrete frequency obtained for each Fourier transform frame described above are respectively coded with high efficiency. In the transmission method of the acoustic signal to be transmitted after the above, the number of quantization bits of the phase component for each discrete frequency obtained for each Fourier transform frame described above is set to the frequency value and the amplitude component. And a transmission method of an acoustic signal for transmitting the compressed phase component of the data amount by quantizing the phase component according to the number of quantization bits described above. To do.

[0027]

The signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length is discretely Fourier transformed using the same window function, and each Fourier transform frame described above. Using the same predetermined number of data for each discrete frequency obtained as a result of each Fourier transform, within the amplitude component and the phase component for each discrete frequency obtained for each Fourier transform frame described above, A masking curve for each Fourier transform frame is calculated from the amplitude component for each discrete frequency obtained for each Fourier transform frame. Then, the masking curve for each Fourier transform frame is used to compress the data amount of the amplitude component of the corresponding Fourier transform frame. The data of the difference in the amplitude component for each successive Fourier transform frame whose data amount is compressed is subjected to adaptive quantization and transmitted. In addition, discrete Fourier transform is performed on the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined fixed time length, by discrete Fourier transform using the same window function, and for each Fourier transform frame described above. Using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform of, the number of quantization bits of the phase component for each discrete frequency obtained for each Fourier transform frame is calculated as the value of the frequency. And the magnitude of the amplitude component are used as parameters to transmit the phase component in which the data amount is compressed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific contents of the acoustic signal transmission method of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration example of an encoder used in the acoustic signal transmission method of the present invention, and FIG. 2 is a block diagram showing a configuration example of a decoder used in the acoustic signal transmission method of the present invention.
3 to 7 are diagrams used for explaining the configuration and operation, FIG. 8 is a diagram showing a two-dimensional array of allocated bits used in adaptive quantization of phase components, and FIG. 9 is a proposed acoustic signal. 1 is a block diagram showing a configuration example of an encoder used in the transmission method of FIG. 1, FIG. 10 is a block diagram showing a configuration example of a decoder used in the already proposed transmission method of an acoustic signal, FIG.
1 and 12 are diagrams for explaining the configuration principle and operation of a proposed acoustic signal transmission method. FIG. 1 is a diagram showing an example of the configuration of an encoder used in the acoustic signal transmission method of the present invention.
The same reference numerals as those used in the encoder shown in FIG. 9 are used for the components corresponding to those in the encoder used in the already proposed method of transmitting an acoustic signal described with reference to FIG. In FIG. 2 showing the configuration example of the decoder used in the acoustic signal transmission method of the present invention, the already-proposed acoustic signal transmission method described above with reference to FIG. 10 is used. The same reference numerals as those used in the encoder shown in FIG. 10 are used for the components corresponding to those in the encoder used.

In FIG. 1, which shows an example of the configuration of an encoder used in the method for transmitting an acoustic signal of the present invention, 1 is an input terminal for a digital acoustic signal to be recorded and transmitted, Sequential Fourier transform frames cut out from the digital audio signal supplied to the audio signal input terminal 1 so as to have a predetermined fixed time length in an overlapped state by the block 2 are, for example, respectively. A window function is applied for each period having N sampling points, and a window is provided in block 3 so that a sequential one frame period in which the joints of each successive frame are overlapped with each other and gently connected is obtained. After the function is multiplied, the fast Fourier transform operation (FF
T calculation) is performed. Then, as a result of the FFT operation in the block 4 described above, the same constant frequency interval f {however, 1 for each Fourier transform frame is obtained.
Number of data in Fourier transform frame for each frame The number of samples is N, the sampling frequency is fs, and f = fs /
A real part (Rea) for every N discrete frequencies having N}.
l) FFT consisting of amplitude and imaginary part (Imag) amplitude
Data of the calculation result is obtained.

As described above, the N discrete frequency data obtained as a result of the FFT operation is subjected to signal processing by different signal processing devices for each discrete frequency data. However, in FIG. 1, only the configuration of one signal processing device among the N signal processing devices is shown as a block 6 shown by a dashed-dotted line, which is displayed as Cartesian coordinate → polar coordinate conversion in the drawing. It is shown between the multiplexer 18. Data of a specific discrete frequency, which is obtained as a result of the FFT operation and is composed of a real number part and an imaginary number part for each of N discrete frequencies, is polar coordinate-converted by the orthogonal coordinate → polar coordinate converter 6 and becomes an amplitude term. After being separated into the phase term, the amplitude calculation by the above-described Equation 1 is performed by the amplitude calculation unit 6A, and the phase calculation by the already-described Equation 2 is performed by the phase calculation unit 6P, so that the sequential calculation is performed. For each discrete frequency described above for the frame, the composite amplitude term A
i (m) and the phase term θi (m) are obtained. Then, the above-described Cartesian coordinate → polar coordinate conversion unit 6 has an amplitude calculation unit 6
The composite amplitude term Ai (m) of a specific discrete frequency obtained as the calculation result in A is supplied to the masking processing unit 5 and the look-up table (LUT) 39, and the above-mentioned Cartesian coordinates → Polar coordinates. Phase calculator 6 in converter 6
The phase term θi (m) of a specific discrete frequency obtained as the calculation result of P is supplied to the latch circuit 10, the subtractor 14, and the fixed contact a of the changeover switch 16S.

Amplitude calculation section 6 of Cartesian coordinate to polar coordinate conversion section 6
In the masking processing unit 5 to which the composite amplitude term Ai (m) of the specific discrete frequency obtained as the calculation result in A is supplied, the amplitude components in the supplied sequential Fourier transform frames are illustrated in FIG. The masking process is performed in the same procedure as described above. That is, the masking curve mask (m) is calculated using the above-described specific discrete frequency composite amplitude term Ai (m). The calculation of the masking curve mask (m) is performed as follows, for example. To do. A composite amplitude term Ai of a specific discrete frequency
Considering (m) as a set of a single sine wave, the masking curve ms (k) of the single sine wave is used to calculate the range −l1 to l2 by the formula shown in the equation (3). The single sine wave masking curve ms (k) is calculated in order to obtain the masking curve mask (m) with higher accuracy.
The value of ms (k) may be changed depending on the frequency value.

[0032]

[Equation 3]

Next, the so-called loudness curve corresponding to the human auditory perception characteristic that the human auditory sense is low in the low and high frequencies is used to correct the calculation result obtained according to the above-mentioned Equation 3 to obtain the final result. Determine the masking curve mask (m). Then, in the masking processing unit 5, the masking curve mask (m) determined as described above is used to mask the amplitude component Ai (m) as shown in FIG. 3, that is, Ai (m )> Mask
Ai (m) in the case of (m) outputs it as it is, and Ai (m) in the case of Ai (m) <mask (m)
(M) compresses the data amount of the amplitude component by performing signal processing to make it zero. The amplitude component Ai whose data amount is compressed in the masking processing unit 5 as described above
(M) is a latch circuit 7, a subtractor 8 and a changeover switch 9S
Is supplied to the fixed contact a. Changeover switch 9 described above
The movable contact v of S has a composite amplitude term Ai (m) of a specific discrete frequency obtained as a calculation result in the amplitude calculating section 6A of the rectangular coordinate → polar coordinate converting section 6 by the switching signal supplied to the terminal 34. ) And the residual data output from the subtracter 8 are selected and output to the multiplexer 18. The changeover operation of the changeover switch 9S described above is performed in conjunction with the changeover operation of the changeover switch 16S described later.

The changeover switch 9S described above is in a state in which the movable contact v is changed over to the fixed contact a side by the changeover control signal supplied to the terminal 34 at the time of transmitting the data of the amplitude component in the Fourier transform frame to be transmitted first. In this state, the amplitude component output from the masking processing unit 5 is supplied to the adaptive quantizing unit 23 via the fixed contact a and the movable contact v of the changeover switch 9S described above. Further, when the amplitude component data is transmitted in the Fourier transform frame other than the transmission of the amplitude component data in the Fourier transform frame to be transmitted first, the movable contact v of the changeover switch 9S is changed to the fixed contact b of the changeover switch 9S. Side, the residual data output from the subtractor 8, that is, the masking processing unit 5
, The amplitude component Ai in the state where the data amount is compressed with respect to the amplitude components in the Fourier transform frame
The residual difference between (m) is supplied to the adaptive quantization unit 23 from the movable contact v of the changeover switch 9S. As a mode of switching the movable contact v of the changeover switch 9S, for example, the movable contact v may be switched to the fixed contact a side every predetermined number of Fourier transform frame periods, or may be switched in other switching modes. You may

In the adaptive quantizer 23, the amplitude component output via the changeover switch 9S as described above is
Adaptive quantization processing is performed in the procedure as shown in FIG. That is, the adaptive quantizer 23 first detects the maximum absolute value max (k) of the residual component ΔAi (m) of the amplitude supplied thereto for each band, and then detects it for each band as described above. The required number of bits bit (k) is determined for each maximum value max (k) of the absolute value of the amplitude residual component ΔAi (m). Then, based on the above-mentioned max (k) and bit (k), the residual ΔAi (m) of the amplitude which is not in the zero state is adaptively quantized and a data existence flag is set. The adaptively quantized amplitude data ΔAi ′ (m), that is, ΔAi ′ (m) = {ΔAi (m) / max (k)} is supplied to the multiplexer 18.

As a supplementary note regarding the adaptive quantization performed by the adaptive quantizer 23, the masking curve mas
Amplitude component Ai (m) masked by k (m), that is, amplitude component Ai (m) <masking curve mask
Since the amplitude component Ai (m) having the relationship of (m) cannot be heard, it is not necessary to transmit the data of such an amplitude component, and the flag (flag1, flag indicating whether or not the data exists). send flag0). Also,
An amplitude component Ai (m) that is not masked by the masking curve mask (m), that is, an amplitude component A having a relationship of amplitude component Ai (m)> masking curve mask (m).
It is not necessary to send all data for i (m) either, and the maximum value max (k) (k is 0 to 3 to 6 for each frequency band).
The number of bits required for each frequency band based on the maximum value max (k) detected for each frequency band bit (k) {bit (k) is, for example, about 14 bits at maximum. } Should be allocated. Then, in the adaptive quantizing unit 23, it is necessary for each frequency band based on the maximum value max (k) detected for each frequency band and the maximum value max (k) detected for each frequency band. The number of bits bit (k) is used to quantize the amplitude component in which data exists depending on the state of the flag, and the adaptively quantized amplitude component data Ai ′ (m), that is, Ai ′ (m).
= {Ai (m) / max (k)} or ΔAi '(m) =
{ΔAi (m) / max (k)} is calculated and supplied to the multiplexer 18.

The data of the amplitude component supplied to the multiplexer 18 as described above and sent from the multiplexer 18 to the output terminal 19 is highly efficient coded in both the frequency axis direction and the time axis direction. Since it is in a state in which it is in a state in which it is in a state in which data is significantly compressed as compared with the case of performing high efficiency encoding by the conventional high efficiency encoding method described above, the conventional method Compared with, it becomes possible to perform highly efficient coding, in which the same window function is applied to the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length. Fourier transform is performed discretely by using the Fourier transform for each Fourier transform frame, and the same predetermined number of data for each discrete frequency obtained as the result of the Fourier transform for each Fourier transform frame is used. The amplitude and phase components of each discrete frequency obtained for each frame, because each of them so as to transmit after high efficiency coding individually.

Phase calculator 6 of Cartesian coordinates → Polar coordinates converter 6
The phase θi of the i-th specific discrete frequency in the m-th Fourier transform frame obtained as the calculation result of P
(m) is a latch circuit 10, a subtractor 14, and a changeover switch 1
It is supplied to the fixed contact a of 6S. The phase θi output from the phase calculation unit 6P of the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the i-th specific discrete frequency (which is now assumed to be fa) in the m-th Fourier transform frame. The data of (m) is the data of the phase held in the latch circuit 10 before it is held in the latch circuit 10, that is, the calculation of the phase of a specific discrete frequency fa in the m-1 th Fourier transform frame. As a result, the data of the phase θi (m-1) output from the phase calculator 6P of the rectangular coordinate → polar coordinate converter 6 is composed of the latch circuit 12, the amplifier 11 having a gain of 2, and the subtractor 13. It is held in the latch circuit 12 in the phase prediction unit PFC.

The phase data held in the latch circuit 12 before the above-mentioned phase θi (m-1) data is held in the latch circuit 12, that is, a specific discrete value in the m-2th Fourier transform frame. The data of the phase θi (m−2) output from the phase calculator 6P of the rectangular coordinate → polar coordinate converter 6 as the calculation result of the phase of the frequency fa is supplied to the subtractor 13 as a subtraction signal. And again
Since the output from the amplifier 11 having a gain of 2 is supplied to the subtractor 13 as the minuend signal, the predicted phase data output from the subtractor 13, that is, the phase The predicted phase data output from the prediction unit PFC is 2θi (m-1) −θi (m-2). Then, the predicted phase data 2θi (m-1) -θi (m-2) output from the phase predicting unit PFC is subtracted from the actual phase data θi (m) in the subtractor 14, From the subtracter 14, the phase residual (signal) θi (m)
-{2θi (m-1) -θi (m-2)} is output and supplied to the fixed contact b of the changeover switch 16S.

As described above, the changeover switch 16S is supplied with the changeover control signal to the control signal supply terminal 36 so as to perform the changeover operation in synchronization with the changeover switch 9S. The movable contact v of the changeover switch 16S is switched to the fixed contact a side by the changeover control signal supplied to the terminal 36 at the time of transmitting the phase component data in the Fourier transform frame to be transmitted first. In such a switching state, the data of the initial setting value of the phase component output from the phase calculating unit 6P, for example, the phase component data θi (0) is transferred to the fixed contact a of the changeover switch 16S. It is supplied to the adaptive quantizing unit 17A via the movable contact v, and at the time of transmitting the phase component data in the Fourier transform frame other than the above-described first transmission of the phase component data in the Fourier transform frame, The movable contact v of the selector switch 16S is switched to the fixed contact b side, and the subtractor 14
Residual data Δθ (m) output from, that is, Δθ
Since (m) = θi (m)-{2θ1 (m-1) -θi (-2)} is supplied to the adaptive quantization unit 17A via the fixed contact b and the movable contact v of the changeover switch 16S. is there.

In the adaptive quantizing unit 17A, the look
By referring to the up table 39, the data of the phase component supplied through the movable contact v of the changeover switch 16S described above is adaptively quantized and supplied to the multiplexer 18. The above-mentioned look-up table 39 stores the data of the number of bits for which the required number of bits is determined by using the signal level (amplitude) value and the frequency value as parameters. When the frequency value and the address signal are given, the data of the bit number corresponding to the address is given to the adaptive quantizing unit 17A, and the fixed contact a (or b) and the movable contact of the changeover switch 16S are provided. The phase component supplied to the adaptive quantizing unit 17A via v is converted into data having a bit number corresponding to the bit number read from the look-up table 39, and output from the adaptive quantizing unit 17A. It An address signal is supplied to the look-up table 39 from the amplitude calculator 6A. FIG. 6 shows a procedure of adaptive quantization in the adaptive quantization unit 17A.

In FIG. 8, the signal level (amplitude) value and the frequency value are used as parameters to store the data of the number of bits for which the required number of bits has been determined.
It is a figure which illustrates the two-dimensional arrangement | sequence aspect of the number of bits in the look-up table which is made to be able to output the data of a predetermined bit number according to the (amplitude) value and the frequency value. . Where signal level (amplitude) as described above
An example of how to determine the number of bits required to configure a look-up table capable of outputting a predetermined number of bits of data according to a value and a frequency value will be described below. is there. First, prepare many kinds of sine wave signals with different amplitude and frequency,
Using one kind of sine wave signal selected from the above-mentioned many kinds of sine wave signals, each signal having a predetermined fixed time length (each Fourier transform frame) is cut out and discretely (for example, 1024 Point) is subjected to Fourier transform, and the amplitude component and the phase component are obtained using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each Fourier transform frame.

For the phase components obtained by using the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each Fourier transform frame obtained as described above, the Fourier transforms adjacent to each other on the time axis Find the difference between the phase components in the frame. With respect to the value of the difference between the phase components described above, data is rounded with various bit numbers based on 2π. An inverse Fourier transform is performed on the above-mentioned data to restore the signal. The minimum number of bits within a range in which the difference between the sound sense of the listener due to the sound field generated by the restoration signal and the sound sense of the listener due to the sound field generated by the original sine wave signal is allowable is determined. It should be noted that the signal to be used is not limited to the sine wave signal as described above, and may be any signal as long as the amplitude and the repetition frequency can be defined. The number of bits can be determined with.

In the adaptive quantizing unit 17A, adaptive quantizing is performed by the means shown in FIG. 6, the quantizing size is set according to the frequency and the amplitude, and then supplied to the multiplexer 18. In the multiplexer 18, the output data from the signal processing circuit is obtained by combining the amplitude residual signal of a specific discrete frequency (probably fa now) with the phase residual signal of the specific discrete frequency fa. Is output to the output terminal 19. Data output from the signal processing circuit shown in FIG. 1 and another signal processing circuit having a configuration similar to that of the signal processing circuit shown in FIG. 1 (a specific discrete frequency is other than fa) The output data from the signal processing circuit which processes the signal of the frequency of is transmitted as the data of the acoustic signal in the state where the information amount is compressed on the same transmission path.

Next, an example configuration of the receiving side of the transmission system will be described with reference to FIG. In FIG. 2, reference numeral 20 denotes an input terminal of the signal processing circuit for a signal of a specific discrete frequency (which is assumed to be fa) among a large number of signal processing circuits provided on the receiving side. Another signal processing circuit having the same configuration as that of the signal processing circuit shown in FIG. 2 (a signal processing circuit for processing a signal having a specific discrete frequency other than fa) is shown in FIG. Is omitted. The specific discrete frequency (now,
The signal of the amplitude component (for example, fa) and the signal of the phase component are separated by the de-multiplexer 21 that separates the signal of the amplitude component and the signal of the phase component to obtain the amplitude of the specific discrete frequency. The component signal is supplied to the inverse quantizer 37, and the phase component signal of the specific discrete frequency is supplied to the inverse quantizer 38.

In the dequantizer 37, the signals flag (m), max (k), bit (k) and ΔAi '(m described above sent from the encoder side in association with the amplitude component are sent. ) ΔAi ′ (m) in FIG. 5 is ΔAi (m) = Δ shown in FIG.
Dequantize by an operation such as Ai '(m) · max (k),
The output data ΔAi (m) is added to the adder 25 and the changeover switch 26.
It is supplied to the fixed contact a of S. Changeover switch 2 described above
The movable contact v of 6S is switched between the fixed contacts a and b by the switching control signal supplied to the switching control signal supply terminal 41. A switching control signal supplied to the switching control signal supply terminal 42 of the switching switch 30S so that the movable contact v of the switching switch 26S and a movable contact v of the switching switch 30S, which will be described later, are interlocked. The switching control signal supplied to the switching control signal supply terminal 41 is the same signal. Changeover switch 26 described above
The movable contact v of S and 30S needs to be switched to the fixed contact a side only during the period of the first frame, but in order to prevent malfunction on the transmission side due to accumulation of prediction errors. Therefore, in the case where the movable contact v is switched to the fixed contact a side in appropriate frame intervals every time other than the period of the first frame, the changeover mode of the changeover switches 9S and 16S on the transmission side is changed. Try to synchronize with.

From the latch circuit 24 in FIG. 2 to the adder 2
The data given to 5 is the inverse quantizer 37 described above.
From the amplitude component data given to the adder 25 from
When the data is the amplitude component data in the m-th Fourier transform frame, it is the amplitude component data Ai (m-1) in the m-1th Fourier transform frame. Therefore, in the above case, the adder 25 adds the data Ai (m-1) of the amplitude component of the m-1 th Fourier transform frame and the data of the amplitude component of the m th Fourier transform frame, From 25, the data Ai (m) of the amplitude component of the m-th Fourier transform frame is output, which is held by the latch circuit 24 and at the same time the polar coordinate → orthogonal coordinate transforming section 27.
Is supplied to.

Further, as described above, the demultiplexer 2
Specific discrete frequencies separated by 1 (for example, fa
Of the amplitude component and the phase component of the phase component are supplied to the inverse quantizer 38, and the inverse quantizer 3
In 8, the data is dequantized by the procedure as shown in FIG. In the inverse quantizer 38, as shown in FIG. 7, the information Ai (m) on the magnitude of the amplitude component of the separated specific discrete frequency (which is now assumed to be fa) and the Fourier transform frame. And the information m indicating the number of the frame of the lookup table 4 from the amplitude component processing unit.
By supplying 0, information of the required number of bits is supplied from the look-up table 40 to the inverse quantizer 38, whereby the inverse quantizer 38 sets the flag flag (m).
Based on, bit (m) bits are used to calculate Δθi '(m) from 0 to 2π.
Dequantize in the range of. Look up table 40
Is the signal level (amplitude) as already described with reference to FIG.
The required number of bits is stored in a two-dimensional array manner using the value and the frequency value as parameters.

The phase component data output from the inverse quantizer 38 is supplied to the adder 29 and the fixed contact b of the changeover switch 30S. The data output from the adder 29 is the data θi of the phase component of a specific discrete frequency in the m-th Fourier transform frame.
(m) means that 2 is added by the adder 29 described above.
The phase component given to the adder 29 from the inverse quantizer 38 is the phase component in the m-th Fourier transform frame, and the two data output from the phase predicting unit PFC.
This is because θi (m-1) −θi (m-2). Data θi of the phase component of a specific discrete frequency in the m-th Fourier transform frame output from the adder 29
(M) is supplied to the polar coordinate → rectangular coordinate conversion unit 27 via the fixed contact b and the movable contact v of the changeover switch 30S and is also supplied to the latch circuit 28.

The phase data held in the latch circuit 28 before the phase component data θi (m) output from the adder 29 is held in the latch circuit 28,
That is, the data of the phase θi (m−1) of the specific discrete frequency fa in the m−1 th Fourier transform frame is composed of the latch circuit 12, the amplifier 11 having a gain of 2, and the subtracter 13. It is held in the latch circuit 12 in the phase prediction unit PFC. Before the data of the phase θi (m-1) is held in the latch circuit 12, the latch circuit 12
The data of the phase held in, that is, the data of the phase θi (m-2) of the specific discrete frequency fa in the m-2th Fourier transform frame is supplied to the subtractor 13 as a subtraction signal. Since the output of the amplifier 11 having a gain of 2 is supplied to the subtractor 13 as a minuend signal, the subtracter 1
The data of the predicted phase output from No. 3, that is, the data of the predicted phase output from the phase prediction unit PFC is 2θi (m-
1) −θi (m-2). Therefore, the phase prediction unit PFC described above
Predicted phase data output from 2θi (m-1) −θi (m-2)
And the phase component of the m-th Fourier transform frame = θi
When (m)-(2θi (m-1) -θi (m-2)) is added by the adder 29, the data output from the adder 29 is a specific discrete data in the m-th Fourier transform frame. It becomes the data θi (m) of the phase component of the proper frequency fa.

M output from the adder 25 as described above
Data Ai of the amplitude component of the th Fourier transform frame
(m) and the data θi (m) of the specific discrete frequency component in the m-th Fourier transform frame output from the adder 29 are supplied to the polar coordinate → orthogonal coordinate transforming unit 27, whereby polar coordinate → orthogonal In the coordinate transformation unit 27, the data Ai (m) of the amplitude component of the m-th Fourier transform frame and the data of the phase component of a specific discrete frequency in the m-th Fourier transform frame output from the adder 29. According to θi (m), the real part (Real) amplitude and the imaginary part (Imag) amplitude at the specific discrete frequency fa described above are calculated and output, and are supplied to the inverse FFT operation unit 31. . Since the inverse FFT operation unit 31 is supplied with output data from all the signal processing circuits provided for each predetermined number of discrete frequencies in the Fourier transform frame, the inverse FFT operation unit 31 described above. To restore the original acoustic signal, and by applying it to the window function multiplication shown in block 32 and the overlap addition shown in block 33, the original acoustic signal is restored. Will be output to the output terminal 35.

[0052]

As is clear from the above description, the method of transmitting an acoustic signal according to the present invention is such that each of the successive Fourier signals cut out from the acoustic signal has a predetermined fixed time length. The discrete Fourier transform is performed on the signal of the transform frame using the same window function, and the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each Fourier transform frame described above is used for the above-mentioned. Among the amplitude component and the phase component for each discrete frequency obtained for each Fourier transform frame, the muff for each Fourier transform frame is used from the amplitude component for each discrete frequency obtained for each Fourier transform frame described above. Then, the data amount of the amplitude component of the corresponding Fourier transform frame is compressed, and the difference data of the amplitude component of each successive Fourier transform frame is compressed. Adaptively quantized and transmitted, and discrete Fourier transform using the same window function for the signals of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined fixed time length. Then, using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform for each Fourier transform frame,
The number of quantization bits of the phase component for each discrete frequency obtained for each Fourier transform frame described above is determined by using the frequency value and the magnitude of the amplitude component as parameters, and the phase component with the compressed data amount is obtained. According to the acoustic signal transmission method of the present invention, the amplitude of the amplitude component and the phase component of the conventional acoustic signal are improved by efficient prediction and adaptive quantization. By applying the efficiency compression method, it is possible to provide a method of transmitting an acoustic signal having a higher compression rate than the method of transmitting an acoustic signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an encoder used in an acoustic signal transmission method of the present invention.

FIG. 2 is a block diagram showing a configuration example of a decoder used in the acoustic signal transmission method of the present invention.

FIG. 3 is a diagram used for explaining a configuration and an operation.

FIG. 4 is a diagram used for explaining a configuration and an operation.

FIG. 5 is a diagram used for explaining a configuration and an operation.

FIG. 6 is a diagram used for explaining a configuration and an operation.

FIG. 7 is a diagram used for explaining a configuration and an operation.

FIG. 8 is a diagram showing a two-dimensional array of allocated bit numbers used in adaptive quantization of phase components.

FIG. 9 is a block diagram showing a configuration example of an encoder used in an already proposed transmission method of an acoustic signal.

FIG. 10 is a block diagram showing a configuration example of a decoder used in the already proposed transmission method of acoustic signals.

FIG. 11 is a diagram for explaining a configuration principle and an operation of a proposed acoustic signal transmission method.

FIG. 12 is a diagram for explaining a configuration principle and an operation of a proposed transmission method of an acoustic signal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal of a digital acoustic signal to be recorded and transmitted, 5 ... Masking processing section, 6 ... Cartesian coordinate → polar coordinate conversion section, 6A ... Amplitude calculation section, 6P ... Phase calculation section, 7,
10, 12, 24, 28 ... Latch circuit, 8, 13, 14
... Subtractor, 9, 16, 26, 30 ... Data selector, 9
S, 16S, 26S, 30S ... Changeover switch, 11 ... Amplifier with gain of 2, 17A, 23 ... Adaptive quantizer, 18 ...
Multiplexer, 19 ... Output terminal, 20 ... Decoder input terminal, 21 ... De-multiplexer, 25, 29 ... Adder, 27 ... Polar coordinate → Cartesian coordinate transformation unit, 31 ... Inverse FFT operation unit, 37, 38 ... Inverse quantization Bowl, 39, 40 ... look
Up table, PFC ... Phase predictor,

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 18, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The phase θm of the specific discrete frequency obtained as the calculation result of the Cartesian coordinate → polar coordinate conversion unit 6 is
It is supplied to the latch circuit 10, the subtractor 13, and the data selector 16. Before the data of the phase θm output from the Cartesian coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency (probably fa) in the m-th frame is held in the latch circuit 10. Latch circuit 1
The phase data held at 0, that is, the phase θi (m−1) output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the m−1th frame. Data of the latch circuit 12
Is held in the latch circuit 12 in the phase predicting unit PFC which is composed of an amplifier 11 having a gain of 2 and a subtractor 13. The terminal 15 is a shift clock signal supply terminal. The data of the phase held in the latch circuit 12 before the data of the phase θi (m−1) is held in the latch circuit 12, that is, the specific discrete frequency fa in the m−2nd frame. The data of the phase θi (m−2) output from the Cartesian coordinate → polar coordinate conversion unit 6 as the result of the phase calculation is supplied to the subtractor 13 as a subtraction signal, and to the subtractor 13 described above. Since the output from the amplifier 11 having a gain of 2 is supplied as the augend signal, the predicted phase data output from the subtracter 13, that is, the phase prediction unit PFC is output. The predicted phase data is 2θi
(M−1) −θi (m−2) {see FIG. 12}.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9]

[Procedure amendment]

[Submission date] October 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

The block diagram shown in FIG. 9 is an application of the phase prediction technique for acoustic signals based on the Takahashi's hypothesis as described above.
When the information amount of the signal to be recorded and transmitted is compressed and then recorded and transmitted, the amplitude residual signal Ai (m) -Ai (m-1) and the phase residual signal are calculated for each frame. Difference signal Δθi (m) = θei (m)-{2θi (m-1) -θ
i (m-2)} is shown as an example of the configuration of an encoder configured to record and transmit, and FIG. 10 shows an example of the configuration of a decoder. FIG. 12 is a diagram showing the predicted value of the phase and the residual value in the decoder shown in FIG. Each of the above residual signals becomes zero if the prediction is correct, but usually a slight deviation from the predicted value occurs, so the above residual signals rarely become zero but the original signal The information amount of the residual signal is much smaller than the information amount.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The phase θm of the specific discrete frequency obtained as the calculation result of the Cartesian coordinate → polar coordinate conversion unit 6 is
It is supplied to the latch circuit 10, the subtractor 13, and the data selector 16. Before the data of the phase θm output from the Cartesian coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency (probably fa) in the m-th frame is held in the latch circuit 10. Latch circuit 1
The phase data held at 0, that is, the phase θi (m−1) output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the m−1th frame. Data of the latch circuit 12
Is held in the latch circuit 12 in the phase prediction unit PFC which is composed of the amplifier 11 having a gain of 2 and the subtractor 13. The terminal 15 is a shift clock signal supply terminal. The data of the phase held in the latch circuit 12 before the data of the phase θi (m−1) is held in the latch circuit 12, that is, the specific discrete frequency fa in the m−2nd frame. The data of the phase θi (m−2) output from the Cartesian coordinate → polar coordinate conversion unit 6 as the phase calculation result is supplied to the subtractor 13 as a subtraction signal, and is supplied to the subtractor 13 described above. Since the output from the amplifier 11 having the gain of 2 is supplied as the minuend signal, the data of the predicted phase output from the subtractor 13, that is, the prediction output from the phase predicting unit PFC. Phase data is 2θi
(M−1) −θi (m−2) {see FIG. 12}.

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9] ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 23, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Further, as described above, the demultiplexer 2
Specific discrete frequencies separated by 1 (for example, fa
The original amplitude component Ai (m), the phase component θi (m), and the phase component θi (m) and the phase residual in the amplitude residual signal ΔAi (m) and the phase residual signal Δθi (m). The difference signal Δθi (m) is requantized by the requantizer 22, and then added by the adder 29 and the data selector 30.
Is being supplied to. The fact that the data output from the adder 29 becomes the data θi (m) of the phase term of the specific discrete frequency in the m-th frame means that the two data added by the adder 29 are , The phase residual signal Δθi (m) given to the adder 29 from the demultiplexer 21 is the phase residual signal Δθi (m) in the m-th frame and 2θi (m output from the phase prediction unit PFC. This is because −1) −θi (m−2). Data θ of a specific discrete frequency phase term in the m-th frame output from the adder 29
i (m) is supplied to the polar coordinates → rectangular coordinates conversion unit 27 via the data selector 30, and the latch circuit 28
Is being supplied to. A shift clock signal is supplied to the terminal 43.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

Next, the so-called loudness curve corresponding to the human auditory perception characteristic that the human auditory sense is low in the low and high frequencies is used to correct the calculation result obtained according to the above-mentioned Equation 3 to obtain the final result. Determine the masking curve mask (m). Then, in the masking processing section 5, the masking curve mask (m) determined as described above is used to mask the amplitude component Ai (m) as shown in FIG. 3, that is, Ai (m )> Mas
Ai (m) in the case of k (m) outputs it as it is, and Ai (m) in the case of Ai (m) <mask (m)
(M) compresses the data amount of the amplitude component by performing signal processing to make it zero. The amplitude component Ai whose data amount is compressed in the masking processing unit 5 as described above
(M) is a latch circuit 7, a subtractor 8 and a changeover switch 9S
Is supplied to the fixed contact a. Changeover switch 9 described above
The movable contact v of S is a composite amplitude term Ai (m) of a specific discrete frequency obtained as a calculation result in the amplitude calculating section 6A of the Cartesian coordinate → polar coordinate converting section 6 by the switching signal supplied to the terminal 44. ) Initial setting data,
Either one of the residual data output from the subtracter 8 is selected and output to the multiplexer 18. The changeover operation of the changeover switch 9S described above is performed in conjunction with the changeover operation of the changeover switch 16S described later.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

The above-mentioned changeover switch 9S is in a state in which the movable contact v is changed over to the fixed contact a side by the changeover control signal supplied to the terminal 44 during the transmission of the amplitude component data in the Fourier transform frame to be transmitted first. In this state, the amplitude component output from the masking processing unit 5 is supplied to the adaptive quantizing unit 23 via the fixed contact a and the movable contact v of the changeover switch 9S described above. Further, when the amplitude component data is transmitted in the Fourier transform frame other than the transmission of the amplitude component data in the Fourier transform frame to be transmitted first, the movable contact v of the changeover switch 9S is changed to the fixed contact b of the changeover switch 9S. Side, the residual data output from the subtractor 8, that is, the masking processing unit 5
, The amplitude component Ai in the state where the data amount is compressed with respect to the amplitude components in the Fourier transform frame
The residual difference between (m) is supplied to the adaptive quantization unit 23 from the movable contact v of the changeover switch 9S. As a mode of switching the movable contact v of the changeover switch 9S, for example, the movable contact v may be switched to the fixed contact a side every predetermined number of Fourier transform frame periods, or may be switched in other switching modes. You may

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 10

[Correction method] Change

[Correction content]

[Figure 10] ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 18, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Further, the Cartesian coordinates → polar coordinates conversion unit 6 described above.
The phase term θi (m) of a specific discrete frequency obtained as the calculation result of is supplied to the latch circuit 10, the subtractor 14, and the data selector 16. The data of the phase θi (m) output from the rectangular coordinate → polar coordinate conversion unit 6 is held in the latch circuit 10 as the calculation result of the phase of a specific discrete frequency (probably fa) in the m-th frame. The phase data held in the latch circuit 10 before the operation, that is, the phase θi output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the m−1th frame. The data of (m-1) is held in the latch circuit 12 in the phase prediction unit PFC. The phase predictor PFC described above includes a latch circuit 12, an amplifier 11 having a gain of 2, and a subtractor 13 in the illustrated configuration example.
It is composed of and. The phase data held in the latch circuit 12 before the data of the phase θi (m-1) is held in the latch circuit 12, that is, the specific discrete frequency fa in the (m-2) th frame. The data of the phase θi (m−2) output from the rectangular coordinate → polar coordinate conversion unit 6 as the phase calculation result is supplied to the subtractor 13 as a subtraction signal, and the data is supplied to the subtractor 13. Since the output from the amplifier 11 having the gain of 2 is supplied as the minuend signal, the predicted phase data output from the subtractor 13, that is,
The predicted phase data output from the phase predictor PFC is 2
θi (m-1) -θi (m-2).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

The phase θi (m) of a specific discrete frequency obtained as the calculation result of the Cartesian coordinate → polar coordinate converter 6 described above.
Is a latch circuit 10, a subtractor 13, and a data selector 16
And supplied to. The phase θi output from the Cartesian coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of a specific discrete frequency (now fa) in the m-th frame.
The data of the phase held in the latch circuit 10 before the data of (m) is held in the latch circuit 10, that is, m
The data of the phase θi (m−1) output from the rectangular coordinate → polar coordinate conversion unit 6 as the calculation result of the phase of the specific discrete frequency fa in the −1st frame is the latch circuit 1
Latch circuit 12 in the phase predictor PFC, which is composed of an amplifier 11 having a gain of 2 and a gain of 2, and a subtractor 13.
Held in. The terminal 5 is a shift clock signal supply terminal. The phase data held in the latch circuit 12 before the data of the phase θi (m-1) is held in the latch circuit 12, that is, the specific discrete frequency fa in the (m-2) th frame. The data of the phase θi (m−2) output from the rectangular coordinate → polar coordinate conversion unit 6 as the phase calculation result is supplied to the subtractor 13 as a subtraction signal, and the data is supplied to the subtractor 13. Since the output from the amplifier 11 having the gain of 2 is supplied as the minuend signal, the data of the predicted phase output from the subtractor 13, that is, the phase predictor P
Predicted phase data output from FC is 2θi (m-1)
−θi (m−2) {see FIG. 12}.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

The phase θ output from the adder 29 described above.
Before the data of i (m) is held in the latch circuit 28,
The phase data held in the latch circuit 28, that is, the specific discrete frequency f in the (m-1) th frame
The data of the phase θi (m-1) of a is held in the latch circuit 12 in the phase predicting unit PFC configured by the latch circuit 12, the amplifier 11 having a gain of 2, and the subtractor 13. The data of the above phase θi (m-1) is the latch circuit 1.
The data of the phase held in the latch circuit 12 before being held in 2, that is, the data of the phase θi (m-2) of the specific discrete frequency fa in the m-2th frame is subtracted by the subtractor 13 Is supplied as a subtraction signal to the subtractor 13, and the subtracted signal is supplied to the subtractor 13 because the output from the amplifier 11 having a gain of 2 is used. The predicted phase data output, that is, the predicted phase data θi (m) output from the phase prediction unit PFC is 2θi (m−1) −θi (m
-2). Therefore, the predicted phase data θi (m) = 2θi (m−1) − output from the phase predictor PFC described above.
θi (m-2) and the phase residual signal Δθi of the m-th frame
When (m) = θi (m)-{2θi (m-1) -θi (m-2)} is added by the adder 29, a specific discrete value in the m-th frame is output from the adder 29. The data θi (m) of the phase term of the frequency fa is output.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction content]

As described above, the changeover switch 16S is supplied with the changeover control signal to the control signal supply terminal 36 so as to perform the changeover operation in synchronization with the changeover switch 9S. The movable contact v of the changeover switch 16S is switched to the fixed contact a side by the changeover control signal supplied to the terminal 36 at the time of transmitting the phase component data in the Fourier transform frame to be transmitted first. In such a switching state, the data of the initial setting value of the phase component output from the phase calculating unit 6P, for example, the phase component data θi (0) is transferred to the fixed contact a of the changeover switch 16S. It is supplied to the adaptive quantizing unit 17A via the movable contact v, and at the time of transmitting the phase component data in the Fourier transform frame other than the above-described first transmission of the phase component data in the Fourier transform frame, The movable contact v of the selector switch 16S is switched to the fixed contact b side, and the subtractor 14
Residual data Δθ (m) output from, that is, Δθ
(m) = θi (m)-{2θi (m-1) -θi (m-2)} is supplied to the adaptive quantizing unit 17A via the fixed contact b and the movable contact v of the changeover switch 16S. Of.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction content]

[0052]

As is clear from the above description, the method of transmitting an acoustic signal according to the present invention is such that each of the successive Fourier signals cut out from the acoustic signal has a predetermined fixed time length. The discrete Fourier transform is performed on the signal of the transform frame using the same window function, and the same predetermined number of data for each discrete frequency obtained as a result of the Fourier transform for each Fourier transform frame described above is used for the above-mentioned. Among the amplitude component and the phase component for each discrete frequency obtained for each Fourier transform frame, the masking curve for each Fourier transform frame is calculated from the amplitude component for each discrete frequency obtained for each Fourier transform frame described above. Calculated, using the masking curve for each Fourier transform frame described above,
The data amount of the amplitude component of each corresponding Fourier transform frame is compressed, and the data of the difference in the amplitude component of each successive Fourier transform frame whose data amount is compressed is adaptively quantized and transmitted. The result of the Fourier transform for each Fourier transform frame is obtained by discretely Fourier transforming the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a certain time length using the same window function. The number of quantization bits of the phase component for each discrete frequency obtained for each Fourier transform frame described above is calculated using the same predetermined number of discrete frequency data obtained as Is determined as a parameter, and the phase component whose data amount is compressed is transmitted. Therefore, according to the acoustic signal transmission method of the present invention, For each of the width component and the phase component, efficient prediction and adaptive quantization are applied to apply a high-efficiency compression method for a conventional acoustic signal to an acoustic signal having a higher compression rate than an acoustic signal transmission method. A signal transmission method can be provided.

Claims (2)

[Claims] 1. The Fourier transform is performed discretely by using the same window function on a signal of each successive Fourier transform frame cut out from an acoustic signal so as to have a predetermined constant time length, and each Fourier transform described above. Using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform for each transform frame, the amplitude component and the phase component for each discrete frequency obtained for each Fourier transform frame, respectively, In a transmission method of an acoustic signal to be transmitted after high efficiency encoding, a masking curve for each Fourier transform frame is calculated from the amplitude component for each discrete frequency obtained for each Fourier transform frame described above, and each Fourier transform described above. Means for compressing the data amount of the amplitude component of the corresponding Fourier transform frame using the masking curve for each frame; Obtaining the difference data of the amplitude components for each successive Fourier transform frame in which the data amount is compressed,
A method for transmitting an acoustic signal in which adaptive quantization is applied for transmission. 2. The Fourier transform is discretely Fourier-transformed by using the same window function to the signal of each successive Fourier transform frame cut out from the acoustic signal so as to have a predetermined constant time length, and each Fourier transform described above. Using the same predetermined number of discrete frequency data obtained as a result of the Fourier transform for each transform frame, the amplitude component and the phase component for each discrete frequency obtained for each Fourier transform frame, respectively, In a transmission method of an acoustic signal to be transmitted after high efficiency encoding, the number of quantization bits of the phase component for each discrete frequency obtained for each Fourier transform frame described above, the frequency value and the magnitude of the amplitude component are parameters. And means for transmitting the compressed phase component of the data amount by quantizing the phase component according to the quantization bit number described above. Sound signal transmission method.