JP4344438B2 - Audio signal waveform processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an audio signal waveform processor, which performs a time stretching and pitch shifting by a phase vocoder system, to prevent a noise due to a pre-echo generated by band division from being generated. SOLUTION: The audio signal waveform processor has, as waveform data, the amplitudes and phases of respective band components obtained by dividing an audio signal into the bands, restores an audio signal waveform by reproducing and putting together the band components of the respective bands while performing time compression or expansion according to the waveform data, and performs phase resetting in the beginning of a pre-echo section generated in the audio signal waveform by the band division so that respective restored band components are in phase with the respective original band components shown by the above waveform data.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an audio signal waveform processing apparatus that performs time stretch (time compression / expansion) and pitch shift (pitch conversion) by a phase vocoder method.
[0002]
In the phase vocoder method, the analysis system divides the audio signal waveform of the original sound into a plurality of frequency bands (bands) using a band filter, analyzes the band components of each band individually, and outputs the output amplitude and phase as characteristic parameters. In the synthesis system, the original band components are reproduced using the output amplitude and phase for each band, and the band components of each band are added and synthesized to produce the original audio signal waveform. Restore.
[0003]
FIG. 10 explains the concept of an audio signal waveform processing apparatus using this phase vocoder method. As shown in the figure, the audio signal waveform X (n) is input to a plurality of analysis units 60. In this example, the analysis unit 60 is provided for each band obtained by dividing the frequency of the audio signal waveform into 100 bands. As shown in FIG. 11, each analysis unit 60 has bands 0 to 99 each having an approximate fundamental frequency of an audio signal waveform as a center frequency, and has a configuration as shown in FIG. That is, for example, the analysis unit of the band k multiplies the input audio signal waveform X (n) by the complex frequency sin (ωk) and cos (ωk) at the center (synchronous detection) to obtain the output amplitude value of the band k At the same time, the phase value of the detection output is differentiated to obtain instantaneous frequency information. The instantaneous frequency is a phase change amount (differential value) per unit time at each time point (each position on the time axis of the waveform), and is information indicating a frequency deviation from the center frequency.
[0004]
In the waveform processing apparatus of FIG. 10, waveform data (output amplitude and instantaneous frequency) of each band of the audio signal waveform X (n) is stored in the waveform memory 61. As shown in FIG. 12, the waveform data is stored in the waveform memory 61 with respect to each address addr (0) to addr (n) on the time axis of the audio signal waveform x (n). Each time, amplitude data A and instantaneous frequency data f are stored.
[0005]
The synthesis system includes a band component reproduction unit 62 provided for each band, and each band component reproduction unit 62 includes a time-frequency conversion processing unit 31, a cosine oscillator 33, and a multiplier 33. The time-frequency conversion processing unit 31 has a configuration as shown in FIG. That is, for the input output amplitude value, the interpolation point interpolates / adds the sample point according to the time stretch ratio (time compression / expansion ratio), and the amplitude envelope (change of the amplitude value over time). The amplitude value obtained by compressing / decompressing the indicated envelope is output. For the input instantaneous frequency value, the central angular frequency ωk is added to the instantaneous frequency value. When pitch conversion is performed, the frequency conversion ratio (depending on the degree of pitch shift) is added to the instantaneous frequency value. Value), and interpolated / additionally interpolated sample points according to the time stretch ratio and compressed / expanded the frequency envelope (envelope showing the change over time of the assumed frequency value) Is output.
[0006]
FIG. 15 is a diagram showing how the amplitude value and the instantaneous frequency are interpolated. In the case of time extension, as shown in FIG. 15A, both the original amplitude envelope and the frequency envelope are extended to generate an amplitude value and an instantaneous frequency obtained by extending the time axis. In the case of time compression, as shown in FIG. 15B, both the original amplitude envelope and the frequency envelope are contracted to generate an amplitude value and an instantaneous frequency obtained by compressing the time axis. By this interpolation processing, the time axis of the original audio signal waveform can be arbitrarily compressed / expanded.
[0007]
The instantaneous frequency value processed by the time-frequency conversion processing unit 31 (appropriately time-stretched) is supplied to the cosine oscillator, and the cosine oscillator generates a cosine wave having the frequency of the band. The amplitude envelope processed by the time frequency conversion processing unit 31 is added and output. Thereby, the component signal of the band is reproduced. Furthermore, the original audio signal waveform can be restored by adding and synthesizing the band components of these bands 0 to 99.
[0008]
[Problems to be solved by the invention]
When reproducing an audio signal waveform of a musical tone by the above-described phase vocoder method, the level of an audio signal waveform of a piano or the like greatly changes in time in the attack portion. When such an audio signal waveform is band-divided using a digital filter, a trace, so-called “pre-echo”, appears before each attack in each band.
[0009]
FIG. 9 is a diagram for explaining this pre-echo phenomenon. For the sake of simplicity, FIG. 9 shows a case where the original audio signal waveform is divided into a high frequency band and a low frequency band. A typical attack waveform (a) is separated into a low-frequency component waveform (b) and a high-frequency component waveform (c), and the appearance of pre-echo is shown. It can be seen from the low-frequency component waveform (b) and the high-frequency component waveform (c) that pre-echo occurs in the silent part preceding the original attack waveform (a). The pre-echo of the low-frequency component waveform (b) and the pre-echo of the high-frequency component waveform (c) are out of phase with each other. Therefore, when the low-frequency component waveform (b) and the high-frequency component waveform are finally synthesized with the same phase, The two pre-echoes cancel each other, and the silent part is restored. This is the same even when the number of bands (bands) to be divided is large. If the component waveforms of each band are added and combined after reproduction, the pre-echo cancels each other and becomes a silent part.
[0010]
Such pre-echoes become more severe as the number of taps of the digital filter (FIR filter) used increases, and the generation limit is the number of taps of the filter itself. In general, the pre-echo size is estimated from the delay amount of the filter. Can do.
[0011]
By the way, when time stretch or pitch shift is performed using the phase vocoder method, generally, the waveform of each band does not return to the phase of the original waveform, and the phase changes. For this reason, even after adding and synthesizing after reproducing the band components of each band, the phase of the pre-echo part of the waveform of each band also changes, so these pre-echo parts do not cancel each other. A pre-echo preceding the attachment remains in the synthesized signal.
[0012]
For this reason, normally, in waveform reproduction using a phase vocoder, noise due to pre-echo is generated immediately before the attack, and the attack sound is not crisp and the so-called attack feeling is significantly impaired.
[0013]
The present invention has been made in view of such problems, and an object of the present invention is to prevent generation of noise due to pre-echo generated by band division while using a phase vocoder method.
[0014]
[Means and Actions for Solving the Problems]
The audio signal waveform processing apparatus to which the present invention is applied has, as waveform data, the amplitude and phase of each band component obtained by dividing the audio signal into a plurality of bands, and the band components of each band are used as needed based on this waveform data. The audio signal waveform is restored by reproducing and synthesizing while compressing / decompressing time.
In the audio signal waveform processing apparatus, in order to solve the above-described problem, in the present invention, each band to be restored at the beginning of the pre-echo period with respect to the pre-echo period generated in the audio signal waveform by band division. The phase is reset so that the phase of the component becomes the phase of the original band component corresponding to each of the waveform data.
It is desirable not to perform time compression / expansion of the waveform to be restored in the pre-echo section.
In this way, the phase reset is performed when pre-echo occurs, and the phase of the playback waveform of each band at that point is set to the same as that of the original sound. Pre-echo is canceled in the audio signal waveform.
[0015]
In the above-described phase reset, it is more desirable that the phase of the waveform that has been reproduced so far and the value of the phase to be replaced based on the waveform data are replaced by a cross fade.
In this way, the phase of the reproduced waveform changes continuously at the time of phase reset, so that it is possible to prevent the occurrence of noise due to a discontinuous change in phase due to a sudden change in phase value. .
[0016]
In addition, when the waveform reproduction involves pitch conversion, it is desirable that the degree of phase change based on the pitch conversion and the stepping degree of the read address for reading the waveform data are matched.
Thereby, the phase of the pitch-converted waveform becomes the same as the original waveform, the original phase is reproduced in the reproduction waveform of the band component, and the pre-echo can be canceled by synthesizing each band component.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an audio signal waveform processing apparatus as an embodiment of the present invention. In this embodiment, the present invention is applied to a keyboard-type electronic musical instrument. In the figure, 2 is a CPU (central processing unit) that controls the entire apparatus, 3 is a ROM (read only memory) that stores various table data, a control program for the CPU, and the like, 4 is a plurality of audio signal waveforms. It is a RAM (Random Access Memory) that stores waveform data and is used as a working memory for the CPU. Reference numeral 5 denotes an operator group composed of various operators, such as a selection button for selecting a playback waveform from various waveforms, setting a flexibility to be described later, and instructing start / end of waveform playback. There are various controls. A keyboard device 6 has a lever 61 on the panel for adjusting the reproduction speed. Reference numeral 1 denotes a waveform synthesizing unit, which comprises a waveform memory 10 and band component reproducing units 11-0 to 11-99 provided corresponding to the respective bands. The original audio signal is based on the waveform data selected for reproduction. Restore the waveform and output it.
[0018]
The waveform memory 10 of the waveform synthesizer 1 has an area for storing waveform data of an audio signal waveform and an area for storing reset address information.
[0019]
The waveform data of the audio signal waveform consists of an output amplitude value and a phase value. The output amplitude value is the same as that described in the prior art. The phase value replaces the aforementioned instantaneous frequency value of the prior art and is an original characteristic parameter of the phase vocoder. In the present embodiment apparatus, the waveform data (amplitude value and phase value) of a plurality of types of audio signal waveforms is obtained by analyzing in advance and stored in the RAM 4. Then, the waveform data of the audio signal waveform selected for reproduction by the selection button for waveform selection is stored in the waveform data area of the waveform memory 10.
[0020]
FIG. 2 shows a conceptual configuration of an analysis unit that analyzes an audio signal waveform and extracts waveform data of an output amplitude value and a phase value of each band waveform. As shown in the figure, the audio signal waveform X (n) is multiplied by the band center complex frequencies cos (ωk, n) and sin (ωk, n), respectively, and passed through the analysis filter of the impulse response W (n), The output is squared and then added to calculate a square root to obtain an amplitude value. Further, the outputs Xcos and Xsin of the analysis filter are passed through a calculation unit to obtain a phase value. In the calculation unit, according to the output Xcos and Xsin of the analysis filter,
Arctan (Xsin / Xcos) when Xcos> 0
Arctan (Xsin / Xcos) + π when Xcos <0
And outputs the result as a phase value.
[0021]
The reset address information area of the waveform memory 10 stores reset address information (phase reset information) of the selected audio signal waveform. This reset address information is set to an address at a position before the address indicating the attack of the audio signal waveform by the amount of pre-echo, and is set for each attack waveform existing in time series in the audio signal waveform. Are sequentially assigned as RstAdr (0), RstAdr (1), RstAdr (2)..., And are arranged in the order of their sizes. Note that how far the pre-echo precedes the attack can be estimated from the delay amount of the filter that performs band division.
[0022]
In this embodiment, the reset address information is obtained by analyzing in advance for a plurality of types of audio signal waveforms, and stored in the RAM 4. Then, the reset address information of the audio signal waveform selected for reproduction by the waveform selection button is stored in the reset address information area of the waveform memory 10.
[0023]
The band component reproducing units 11-0 to 11-99 are supplied with an amplitude value, a phase value, and a reset address from the waveform memory 10, and with time position information (reading address DataAdr) and pitch information from the CPU 2 side. Based on these data, the band component of the corresponding band is reproduced and output. The band components output from each of the band component reproducing units 11-0 to 11-99 are added and synthesized with each other to be restored and output as an audio signal waveform.
[0024]
FIG. 3 shows a configuration example of the band component reproduction unit 11. As shown in the figure, the phase value read from the waveform memory 10 is branched into two, one being directly input to the cosine oscillator 32 and the other being input to the differentiating unit 30. The phase value input to the differentiating unit 30 is differentiated to be converted into an instantaneous frequency and input to the time-frequency conversion processing unit 31. The amplitude value read from the waveform memory 10 is input to the time frequency conversion processing unit 31. The time-frequency conversion processing unit 31 has the same configuration as that described in the section of the prior art, and sends the amplitude value to the multiplier 33 and the instantaneous frequency value to the cosine oscillator 32 as in the conventional configuration.
[0025]
The reset address information read from the waveform memory 10 is input to the phase reset signal generator 34. A read address DataAdr (time position information) for reading waveform data from the waveform memory 10 is input to the phase reset signal generator 34. The phase reset signal generator 34 compares the reset address RstAdr read from the waveform memory 10 with the read address DataAdr, generates a phase reset signal when the read address DataAdr exceeds the reset address RstAdr, and sends it to the cosine oscillator 32. To do.
[0026]
FIG. 4 shows a flowchart of a phase reset signal transmission procedure in the phase reset signal generator 34. As shown in the figure, when the read address DataAdr is updated as the waveform is reproduced (step S1), whether the read address exceeds the reset address RstAdr (k), that is,
RstAdr (k) <DataAdr
(Step S2), if it does not exceed, the process ends and waits until the next read address update, and if it exceeds, update the parameter k indicating the order of the reset address, that is, k = k + 1. At the same time, a phase reset signal is generated and transmitted (step S3).
[0027]
FIG. 5 shows a configuration example of the cosine oscillator 32. The phase value data from the waveform memory 10 is input to the adder 42, where the rotation (angular frequency) ωk of the center frequency of the block is added, and the resultant value is input to the summer 40. An instantaneous frequency value from the time frequency conversion processing unit 31 is input to the summer 40, and is converted into an instantaneous phase value by summing, and this instantaneous phase value is supplied to the cosine calculator 41. Then, a cosine wave having a frequency regarded as the frequency of the component signal of the block is generated and output. The phase reset signal is input to the summer. When the phase reset signal arrives, the phase of the instantaneous frequency is replaced with the absolute phase from the adder 42.
[0028]
Next, since the apparatus of this embodiment uses the time compression / expansion rate and flexibility in order to perform time stretching (time compression / expansion) of the audio signal waveform, these will be described. The compression / expansion rate represents the amount of time compression / expansion with respect to the audio signal waveform as a ratio of time length before and after compression / expansion. On the other hand, the flexibility indicates the degree of correction of how the compression / decompression rate is corrected in each section of the audio signal waveform.
[0029]
[Flexibility]
For example, as shown in FIG. 6, the musical sound waveform is divided into a plurality of sections in time (the total number of sections is m), and the flexibility E (i) is set for each section. For example, it is desirable to set this section so as to coincide with a pre-echo section, an attack section, a decay section, a sustain section, a release section, a silent section, and the like.
[0030]
Here, when the degree of flexibility E (i) is “0”, the reproduction speed of the section is maintained as the original waveform regardless of the setting state of the lever 61 and the value of the compression / expansion rate. . When the flexibility is “1”, the playback speed set by the lever 61 is obtained. If the flexibility is less than “1”, the playback speed is set lower than the playback speed set by the lever 61. If the flexibility is higher than “1”, the playback speed is set higher than the playback speed set by the lever 61. Become.
[0031]
The flexibility of each section is set so that the sum of the products of the length of each section of the musical sound waveform and the flexibility in the section becomes the length of all sections. This can be expressed in mathematical formulas:
ΣE (i) x L (i) = ΣL (i) (1)
However, Σ is an addition from i = 0 to (m-1)
L (i) is the length of each section
E (i) is the flexibility in each section
m is the total number of sections
i is a section counter indicating a section being played out of sections from 0 to m
It becomes. Therefore, even if the compression / expansion rate of each section is corrected by the flexibility, the entire compression or expansion time of the waveform data is the value obtained by multiplying the compression / expansion rate by the time of the original waveform data, that is, the entire waveform data. It is simply the time when compression / decompression is performed based on the compression / decompression ratio.
[0032]
As will be described later, in the present invention, the processing according to the present invention is made possible by setting the flexibility E (i) of the pre-echo period to “0”.
[0033]
[Compression / decompression ratio]
The compression / expansion rate is a coefficient for compressing or expanding the time length of the waveform to be reproduced as compared with the time length of the original waveform. That is, in this embodiment apparatus, the waveform reproduction speed can be varied by operating the lever 61 provided on the keyboard 6. The lever 61 has the same playback speed as the original waveform at the midpoint position, which is the automatic return point, and can swing the playback speed forward or backward by swinging back and forth. This reproduction speed has a reciprocal relationship with the compression / expansion rate. For example, when a certain waveform is reproduced at twice the reproduction speed, the time required for reproduction is l / 2 times, which is nothing but the compression / expansion rate is l / 2. When this waveform is reproduced at a reproduction speed of 1/2, the time required for reproduction is doubled. Similarly, this indicates that the compression / expansion rate is 2.
[0034]
The above playback speed is determined based on the step amount (tcomp, tcomp ', tcomp "). The step amount is an amount by which the time position (read address DataAdr) for reproducing the audio signal waveform is stepped, In other words, the waveform reproduction speed, that is, the reciprocal of the time expansion / compression ratio, is set by operating the lever 61.
[0035]
The step amount includes a basic step amount tcomp determined based on the set position of the lever 61, a flexibility correction step amount tcomp 'obtained by correcting the basic step amount tcomp in consideration of the flexibility, and the flexibility. There is a pitch correction step amount tcomp "in which the correction step amount tcomp 'is further corrected in consideration of pitch conversion.
[0036]
First, the basic step amount tcomp is specifically a value that changes between “1” when the lever 61 is in the middle position and, for example, between “+2” and “0” when the lever 61 is tilted back and forth. When the read address DataAdr is updated with the basic step amount tcomp, if the basic step amount tcomp is “1”, the audio signal waveform is reproduced with the original time length, and the basic step amount tcomp is “2”. If there is, the audio signal waveform is reproduced with half the original time length, and if the basic step amount tcomp is “0”, the audio signal waveform is repeatedly reproduced at the same position.
[0037]
The flexibility correction step amount tcomp ′ is obtained by correcting the basic step amount tcomp by the following expression based on the flexibility E (i) of the corresponding section.
tcomp ′ = 1 / [E (i) × {(1 / tcomp) −1} +1]
Here, when the flexibility E (i) is 1, the flexibility correction step amount tcomp ′ becomes the basic step amount tcomp and the playback speed set by the lever 61. When the flexibility E (i) is smaller than l, the value of the flexibility correction step amount tcomp ′ becomes smaller than the basic step amount tcomp and becomes lower than the reproduction speed set by the lever 61. When the flexibility E (i) is larger than 1, the value of the flexibility correction step amount tcomp ′ becomes larger than the basic step amount tcomp and becomes higher than the reproduction speed set by the lever 61. If the flexibility E (i) is set to “0”, the flexibility correction step amount tcomp ′ becomes “l”, which is the reproduction distance of the original waveform. Therefore, although the compression / expansion is performed by setting the flexibility E (i) to “0”, the section M (i) can be reproduced at the reproduction speed of the original waveform. In this case, even if the value of the basic step amount tcomp set by the lever 61 is changed during the reproduction, the flexibility correction step amount tcomp ′ is maintained at “1”. In this way, the CPU 2 corrects the basic step amount tcomp.
[0038]
The pitch correction step amount tcomp "will be described in detail later, but the flexibility correction step amount tcomp 'is further corrected,
tcomp "= W × tcomp '
Ask for. Where W is the degree of correction,
W = (L / tcomp-L0) / (L / tcomp-L0 / P)
It is. Here, “L0” is the interval of 0 flexibility starting from the reset address, and “L” is the length from the reset address of interest to the next reset address.
[0039]
[Generation of read address DataAdr]
When time compression / expansion and pitch shift are not performed, the read address DataAdr is generated by stepping in the order of addresses of the audio signal waveform. The sampling rate of the audio signal waveform data is 44. When it is 1 kHz, it becomes 44.1 kHz. When the playback speed is changed by the lever 61, the read address DataAdr is stepped by the basic step amount tcomp determined by the lever 61. For example, if the basic step amount tcomp is “2”, a read address DataAdr that jumps every other sampling point (address Addr) of the original audio signal waveform is generated (that is, time-compressed). For example, if the basic step amount tcomp is “½”, the read address DataAdr is generated (that is, time-extended) at the intermediate point between the sampling points of the original audio signal waveform.
[0040]
The operation of this embodiment apparatus will be described below.
As described above, with respect to a plurality of audio signal waveforms, the head of each pre-echo part in each audio signal waveform is preset as a reset address, and these reset addresses are stored in the RAM 4 together with the waveform data of the corresponding audio signal waveform. Stored in advance. For these audio signal waveforms, information on the flexibility E (i) is also stored in the RAM 4 in association with each audio signal waveform. In this embodiment, “0” is set as the flexibility E (i) for each pre-echo section.
[0041]
When an arbitrary audio signal waveform is selected using the waveform selection button in the operator group 5, the waveform data and reset address information of the audio signal waveform are transferred to and stored in the waveform memory 10 of the waveform synthesizer 1. Also, the flexibility information is referred to by the CPU 2 to create the read address DataAdr.
[0042]
When the start of waveform reproduction is instructed, the CPU 2 generates a read address DataAdr by referring to the setting state of the lever 61, the flexibility information of the waveform reproduction position, the pitch information, etc. The time position information is supplied to 11-99.
[0043]
The band component reproducing units 11-0 to 11-99 read the waveform data of each band from the waveform memory 10 in accordance with the read address DataAdr, and the band component reproducing units 11-0 to 11-99 reproduce the band components. The processing in the time frequency conversion processing unit 31 in the band component reproduction unit 11 is converted to an instantaneous frequency by differentiating the phase value read from the waveform memory 10 by the differentiating unit 30 and sent to the time frequency conversion processing unit 31. Except for this point, the processing is the same as that described in the prior art.
[0044]
In addition, the reset address RstAdr (n) is read from the waveform memory 10 and input to the phase reset signal generator 34, and the read address DataAdr is compared with the reset address RstAdr (n) in the phase reset signal generator 34. If they match, a phase reset signal is generated and sent to the cosine oscillator 32. When receiving the phase reset signal, the cosine oscillator 32 resets the phase of the generated cosine wave so as to become the phase value of the waveform data input from the waveform memory 10 at that time (that is, the phase of the original sound waveform).
[0045]
As a result, the phase of each band component signal reproduced by each of the band component reproducing units 11-0 to 11-99 at the time position of the reset address RstAdr (n), that is, the start position of the pre-echo period, is the original audio signal waveform. Therefore, if these are added and synthesized, the pre-echo waveforms of the respective band component signals cancel each other and disappear from the restored audio signal waveform. Since the degree of flexibility is set to “0” in the pre-echo period, time compression / expansion is not performed through the same period, so that a phase shift due to time compression / expansion processing does not occur in the reproduction signal. Therefore, the state where the pre-echo waveforms of the respective band component signals to be reproduced cancel each other continues throughout the pre-echo period.
[0046]
When the phase reset signal is input, the operation in the cosine oscillator 32 resets the held phase in the summer 40, and changes the center frequency to the phase value sent directly from the waveform memory 10. Is replaced with a rotation amount ωkn added. The instantaneous frequency value obtained by replacing the phase is supplied to the cosine calculator 41, and a cosine wave having the phase and frequency is generated and output. As described above, since at least the reset address RstAdr (n) to the head address of the attack section is set in advance so that the flexibility is zero, the time position in the section until the attack is started The information (reading address) is a value that faithfully reproduces the original sound, and in this section, the pre-echo waveform that is first divided into bands is reproduced as it is, and thus the pre-echo is canceled at the time of synthesis.
[0047]
The above operation has been described with respect to a case where no pitch conversion (pitch shift) is involved, and the present invention is most effectively used when such a pitch conversion is not involved. Even with the above, the present invention can be applied by performing the following processing.
[0048]
First, a section of 0 flexibility following the reset address is temporarily called a rigid section. For convenience, the length of the rigid section is “L0”, and the length from the reset address of interest to the next reset address is “L”. Further correction is added to the flexibility correction step tcomp 'described above. That is, in the section of flexibility “0” following the reset address,
tcomp "= P
And Here, P is pitch information P (information indicating the amount of pitch shift) supplied to the band component reproduction unit.
[0049]
Further, in each section up to the next reset address, as a step amount, a recorrected pitch correction step amount tcomp "further correcting the flexibility correction step amount tcomp ',
tcomp "= W × tcomp '
Is used. Where W is the degree of correction,
W = (L / tcomp-L0) / (L / tcomp-L0 / P)
It is.
[0050]
This is because in the rigid section, pitch conversion is performed, so that the phase advancement is P times. Therefore, if the basic step amount tcomp is also set to the same value, the phase advance becomes the same as the original waveform, and the original phase is reproduced even in the pitch-converted waveform. Further, since the length of the rigid section becomes 1 / P, the next reset address is adjusted from the reset address by adjusting the step amount of the address of the remaining section until the next reset address comes with the correction degree W. The length to the address is corrected to a desired time length. FIG. 7 shows this state, and the black portion is a rigid section.
Time position information is calculated from this pitch correction step tcomp ".
[0051]
Various modifications are possible in the practice of the present invention. For example, in the above-described embodiment, when the phase is reset by the cosine oscillator, the phase is generally discontinuous, which may cause noise. In general, the phase reset is performed shortly before the attack, and the amplitude at that time is usually very small, so even if the phase of this part is discontinuous, no noise will be generated or no problem will occur. Although small, it can also be improved to further reduce the possibility of this small noise generation.
[0052]
That is, in the cosine oscillator, the phase reset signal is not suddenly reset at the timing of arrival of the phase reset signal, but the sum of the frequency value and the absolute phase (according to the phase of the waveform data in the waveform memory 10) from the arrival of the phase reset signal. The phase is continuously brought close to the absolute phase by so-called cross-fade, which is added while gradually changing the ratio. Although a short time compared with the length of the pre-echo from the reset address is sufficient for the cross-fade time, the reset address can be set in advance so as to be further ahead.
[0053]
FIG. 8 shows a configuration example of a cosine oscillator when performing this crossfade. In this configuration example, a cross-fade calculator 43 is newly provided, and a phase reset signal, an absolute phase, and an output (instantaneous phase value) of the summer 40 are input, and a cross-fade end notification is sent to the summer 40. Configure to send. The crossfade computing unit 43 normally outputs the data from the summer 40 as it is, and starts the crossfade when the phase reset signal arrives. In this crossfade, after the phase is reset, the output signal of the crossfade calculator 43 is set so that the ratio of the absolute phase value gradually increases with time from the instantaneous phase value of the summer 40. At the end of the crossfade, a crossfade end notification is sent to the summer 40, the phase of the summer 40 is rewritten to an absolute phase value, and the output signal from the summer 40 is output as an instantaneous phase value. Change over.
[0054]
In the above-described embodiment, the pre-echo can be removed by generating the phase reset signal at the start position of the pre-echo period. However, this phase reset signal is used when, for example, the audio signal waveform to be reproduced is a faithful reproduction of the original sound (that is, when time compression / decompression is not performed), or when waveform reproduction is started or during reproduction. It may be generated at any point of time. In this way, at the time of the phase reset, each phase of the component signal of each band of the audio signal waveform to be restored matches that of the original sound, so that the reproduced waveform becomes more faithful to the original sound.
[0055]
Further, in the above-described embodiment, it is possible to remove the pre-echo by setting the section of flexibility “0” as the pre-echo section. However, the section of flexibility “0” is set as the attack section, for example. You can also. As described above, when the attack period is set to “0”, even when the audio signal waveform is time-compressed / expanded, the attack part is reproduced as the original sound waveform (that is, the waveform not time-compressed / expanded). Will be. In general, the attack part best represents the characteristics of the musical sound, so if this attack part is compressed / expanded in time, it will sound like a tone different from the original sound, but the attack part is flexible as described above. By setting the degree to “0”, even when the entire waveform is time-compressed / expanded, the characteristics of the musical sound expressed by the attack portion can be well preserved.
[0056]
【The invention's effect】
As described above, according to the present invention, the phase reset signal is generated when the pre-echo occurs, and the phase at that time is set to the same as the original sound. Generation | occurrence | production can be prevented and the crispness of an attack sound can be made good thereby and it can prevent that an attack feeling is impaired.
[Brief description of the drawings]
FIG. 1 is a diagram showing an audio signal waveform processing apparatus as one embodiment according to the present invention.
FIG. 2 is a diagram for explaining a concept of an analysis unit that extracts a phase value and an amplitude value from an audio signal waveform in the embodiment apparatus;
FIG. 3 is a diagram illustrating a configuration example of a band component reproduction unit in the embodiment apparatus;
FIG. 4 is a flowchart showing a processing procedure of transmitting a phase reset signal by a phase reset signal generating unit in a band component reproducing unit of the embodiment apparatus;
FIG. 5 is a diagram illustrating a configuration example of a cosine oscillator in a band component reproduction unit of the example device.
FIG. 6 is a diagram for explaining the concept of flexibility in the embodiment device;
FIG. 7 is a diagram for explaining a waveform shape when accompanied by pitch conversion in the embodiment device;
FIG. 8 is a diagram illustrating another configuration example of the cosine oscillator in the band component reproduction unit in the embodiment apparatus;
FIG. 9 is a diagram for explaining a relationship between an attack waveform and a pre-echo in a band-divided audio signal waveform.
FIG. 10 is a diagram for explaining an overall configuration concept of a conventional audio signal waveform processing apparatus using a phase vocoder method;
FIG. 11 is a diagram for explaining a relationship between components of an audio signal waveform of an original sound and each band obtained by dividing a band.
FIG. 12 is a diagram illustrating waveform data regarding an audio signal waveform of an original sound.
FIG. 13 is a diagram for explaining a concept of analyzing an audio signal waveform and extracting an amplitude value and a phase value in an embodiment apparatus.
FIG. 14 is a diagram illustrating a configuration example of a time-frequency conversion processing unit in a conventional audio signal waveform processing apparatus.
FIG. 15 is a diagram illustrating an example of signal waveform processing in a time-frequency conversion processing unit of a conventional audio signal waveform processing apparatus.
[Explanation of symbols]
1 Waveform synthesis unit
2 CPU (Central Processing Unit)
3 ROM [Read Only Memory]
4 RAM (Random Access Memory)
5 controls
6 Keyboard device
61 Lever for speed adjustment
10 Waveform memory
11 Band component playback section
30 Differentiation part
31 Time frequency conversion processor
32 Cosine oscillator
33 multiplier
34 Phase reset signal generator
40 divider
41 Cosine computation section
42 Adder
43 Crossfade calculator

Claims (4)

By having the amplitude and phase of each band component obtained by dividing the audio signal into a plurality of bands as waveform data, and reproducing and synthesizing the band components of each band while compressing / decompressing them as necessary based on this waveform data. An audio signal waveform processing apparatus for restoring an audio signal waveform,
For the pre-echo period generated in the audio signal waveform by band division, the phase of each band component to be reproduced at the beginning of the pre-echo period is changed to the phase of the original band component corresponding to each of the waveform data. An audio signal waveform processing device configured to reset the phase so that 2. The audio signal waveform processing apparatus according to claim 1, wherein time compression / decompression of the waveform to be restored is not performed in the pre-echo section. 3. The audio signal waveform processing apparatus according to claim 1, wherein the phase reset replaces the phase of the waveform that has been reproduced up to now and the value of the phase to be replaced based on the waveform data by crossfading. 4. When the waveform reproduction involves pitch conversion, the degree of phase change based on the pitch conversion and the stepping degree of the read address for reading the waveform data are matched. Audio signal waveform processing device.

Images