JP3858784B2 - Audio signal time axis companding device, method and program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an audio signal time axis companding apparatus and method for compressing an original audio signal with a desired companding ratio without changing the pitch and sound quality of the original audio signal.
[0002]
[Prior art]
The time axis companding method is broadly divided into two types, that is, processing in the time domain and processing in the frequency domain. In general, processing in the time domain is low in processing load and easy in real time, but it is difficult to obtain good sound quality. On the other hand, the processing in the frequency domain is easy to obtain good sound quality, but the processing load is high in real time even when the time domain representation is converted into the frequency domain representation by FFT, etc. Processing is difficult.
[0003]
[Problems to be solved by the invention]
The present invention has been made in view of this point, and reduces and reduces the amount of data processing when performing data processing in the frequency domain, and a time axis companding apparatus and method for audio signals that can be processed in real time. And to provide a program.
[0004]
[Means for Solving the Problems]
To achieve the above object, an audio signal time-axis companding device according to the first invention of the present application detects a plurality of local peaks of an amplitude envelope of a frequency spectrum from an audio signal divided into frames , and A detection unit that outputs peak amplitude data and phase data for each frame as an analysis frame, and compares the human psychoacoustic characteristic curve with the amplitude data of the analysis frame to determine a local peak smaller than the audio psychological characteristic curve. a data reducing unit that generates analysis frame deleting the amplitude data and phase data, the number of frames per analysis frame unit time was adjusted based on a predetermined time scale modification ratio, the amplitude of the analysis frame adjusted Is the instantaneous frequency obtained by data and the processing of linking adjacent local peaks in the adjusted analysis frame? Characterized in that a synthesizing unit for synthesizing an audio signal based on the calculated phase data.
[0005]
According to the speech synthesizer according to the first aspect of the invention, the peak data of each frame analyzed by the analysis unit is compared with the psychoacoustic characteristic curve by the data reduction unit. The peak data is reduced based on the result of this comparison. For this reason, the load in subsequent peak cooperation part, a phase generation part, and a synthetic | combination part is reduced greatly, and the real-time process of an audio signal is attained.
[0006]
In order to achieve the above object, the audio signal time axis companding method according to the second invention of the present application provides a time axis compensator for an audio signal by a time axis companding apparatus for compressing an original audio signal at a desired compression rate. A companding method for detecting a plurality of local peaks of an amplitude envelope of a frequency spectrum from an audio signal divided into frames, and detecting the amplitude data and phase data of the local peaks for each frame as an analysis frame a step, a data reduction step of generating an analysis frame deleting the amplitude data and phase data of small local peaks than該聴objective psychological characteristic curve is compared with the amplitude data of the analysis frame to human psychoacoustic characteristic curve , adjusted based on the number of frames per said analysis frame unit of time at a given time scale modification ratio, adjusted And characterized by comprising a synthesizing step of synthesizing the audio signal based on the phase data calculated from the instantaneous frequency obtained by the process of linking the local peak adjacent the amplitude data and the analysis frame the adjusted analysis frame To do.
[0007]
To achieve the above object, a time axis companding program for an audio signal according to a third invention of the present application detects a plurality of local peaks of an amplitude envelope of the frequency spectrum from an audio signal divided into frames. A detection step for outputting the amplitude data and phase data of the local peak for each frame as an analysis frame, and comparing the human psychoacoustic characteristic curve with the amplitude data of the analysis frame, the local peak smaller than the audio psychological characteristic curve of the data reduction step of generating an analysis frame deleting the amplitude data and phase data, the analysis was adjusted based on the number of frames per frame unit of time at a given time scale modification ratio, adjusted for the analysis frame By linking the amplitude data and adjacent local peaks of the adjusted analysis frame Based on the phase data calculated from the instantaneous frequency obtained, characterized in that it is configured to perform a combining step of combining the audio signal to the computer.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows the overall configuration of an audio signal time axis companding apparatus according to an embodiment of the present invention. As shown in FIG. 1, the audio signal time axis companding apparatus according to the embodiment of the present invention includes an analysis unit 10, an auditory psychological characteristic evaluation unit 20, a frame adjustment unit 25, a time scaling unit 30, and a synthesis unit 40. It is roughly composed of
[0009]
The analysis unit 10 includes a window function multiplication unit 11, an FFT unit 12, and a spectrum peak detection unit 13. The window function multiplication unit 11 generates a window function such as a Hamming function and multiplies the input audio signal by this window function, thereby cutting out the input audio signal in units of frames. The FFT unit 12 performs fast Fourier transform (FFT) on the input from the window function multiplication unit 11 and outputs frequency spectrum data in units of frames including amplitude data and phase data. The spectrum peak detection unit 13 detects a local peak of the amplitude envelope of the frequency spectrum output from the FFT unit 12 using a peak detection algorithm such as obtaining the maximum value of the amplitude data in the set band. and it outputs the amplitude data and phase data of the detected local peaks as the analysis frame AF _n. At this time, a peak should not be detected only by the sample point of the FFT result, but should be a peak between the sample points using spline interpolation or quadratic interpolation using several sample points having close frequencies. The frequency is also detected as a peak.
[0010]
The auditory psychological characteristic evaluation unit 20 includes a table that stores an auditory psychological characteristic curve. This auditory psychological characteristic curve indicates the characteristic of sound that can be detected by the auditory nerve of the human ear, such as the minimum audible characteristic curve, frequency masking characteristic curve, and loudness characteristic curve described later. Applicable. The auditory psychological characteristic evaluating unit 20 reduces the local peak data detected by the spectrum peak detecting unit 13 based on the auditory psychological characteristic curve.
[0011]
The case where the minimum audible limit characteristic curve is stored in the table of the psychoacoustic characteristic evaluation unit 20 will be described. The minimum audible limit characteristic curve is data indicating the relationship between the smallest level and the frequency of the sound that can be heard when the human ear listens to the sound as shown by the dotted line AS in FIG.
Psychoacoustic characteristic evaluation unit 20, and the minimum audible limit characteristic curve is compared with the local peak detected by the spectral peak detecting unit 13, local value smaller than the minimum limit of audibility characteristic curve AS from analysis frame AF _n The peak data (black circle data in FIG. 2) is deleted and output to the next frame number adjustment unit 25. As a result, the amount of data to be processed by the time scaling unit 30 in the subsequent stage is reduced, so that the amount of time axis companding processing can be reduced.
[0012]
Next, a case where the frequency masking characteristic curve is stored in the table of the auditory psychological characteristic evaluation unit 20 will be described.
Frequency masking refers to a phenomenon in which when a sound of a certain frequency is sensed, it is difficult to hear a sound having an amplitude smaller than that sound and an adjacent frequency. The human ear has a large number of auditory nerves, and the auditory nerve to be stimulated differs depending on the frequency of the sound, and when the auditory nerve corresponding to a certain frequency is stimulated, the auditory nerve corresponding to the adjacent frequency is Conversely, it is suppressed. A frequency masking characteristic curve indicates the degree of suppression.
[0013]
FIG. 3 shows an example of this frequency masking characteristic curve.
Among the local peaks detected by the spectrum peak detector 13, a plurality of large peaks are selected, and straight lines Li and Li ′ extending in the lower right direction and the lower left direction are drawn with the selected local peak Pmi as a vertex. Then, the plurality of Li, to form a frequency masking curve ML connected to Li', reducing the amount of data by deleting the data of the local peak is below the masking curve ML from analysis frame AF _n, the next stage To the frame number adjusting unit 25.
[0014]
It is also possible to reduce local peak data based on both the minimum audible limit characteristic curve and the frequency masking characteristic curve. Thereby, the amount of data reduction can be further increased.
[0015]
Frame number adjustment unit 25, to the data output from the psychoacoustic characteristic evaluation unit 20, so that this data is desired companding ratio, thinning the analysis frame AF _n units, adjustment of the number of frames after repeated I do.
The time scaling unit 30 includes a peak cooperation unit 31 and a phase generation unit 32. After the data output from the psychoacoustic characteristic evaluation unit 20 is thinned out in units of analysis frames, the number of frames on the time axis is adjusted so that a desired companding rate is obtained by repetition, and then the peak cooperation unit As shown in FIG. 4, 31 performs processing for selecting peaks considered to be continuous from local peak data detected in adjacent analysis frames AF _n−1 and AF _n and linking them to each other. . That is, local peaks corresponding to the local peaks f1, f2, f3... Of the past analysis frame AF _n-1 also exist in the current analysis frame AF _n (f1 ′, f2 ′, f3 ′...). Whether or not to do so is checked, and if it exists, the corresponding local peaks are linked. The determination of the correspondence relationship is made based on whether or not the frequency difference between the two local peaks is within a predetermined value, and local peaks having a difference greater than or equal to the predetermined value Δfmax are excluded from the targets of cooperation. At this time, by linking the local peaks having the smallest frequency difference, it is possible to prevent a plurality of local peaks in the past analysis frame AF _{n−1 and} a single local peak in the current analysis frame AF _n from linking. be able to.
[0016]
When this cooperation processing is performed, the difference between the frequencies of the two local peaks that have been cooperated is obtained, and this is differentiated with respect to the time between the analysis frames AF _n-1 and AF _n to obtain an arbitrary position between the frames. The instantaneous frequency fr at can be obtained. For simplicity, the average frequency of two local peaks may be the instantaneous frequency fr.
[0017]
The phase generation unit 32 considers the phase at the local peak (frequency f) associated with the past analysis frame AF _n−1 as the initial phase Φ _AFn−1 , _f, and instantaneously _{takes the} initial phase Φ _AFn− 1, _f . by adding the phase change calculated from the time Delta] t between the frequencies fr and the frame (2πfr × Δt), determining the phase of the sinusoidal components at the corresponding corresponding local peaks of the current frame AF _n (frequency f') be able to. Further, by adding the same phase change to the phase of the linked local peak of the past synthesized frame SF _n−1 , the corresponding local peak phase of the synthesized frame SF _n is obtained. As for the phase of the local peak for which no associated local peak is found, the phase of the corresponding local peak in the analysis frame is directly used as the phase of the synthesized frame.
Note that the amplitude of the composite frame SF _n, the amplitude of the corresponding analysis frame AF _n should be used as is.
[0018]
The combining unit 40 includes an inverse FFT unit 41 and a window function overlapping unit 42. The inverse FFT unit 41 has a function of performing inverse fast Fourier transform (inverse FFT) on the synthesized frame SF _n synthesized by the time scaling unit 30 to convert it into a time domain representation. The window function superimposing unit 42 multiplies the obtained output audio signal in the time domain by the window function, and outputs the audio signal as an audio signal that is overlapped so as to partially overlap in time and expanded in the time axis. Part.
[0019]
Next, the operation of the time axis companding device will be described based on the flowchart shown in FIG. The audio signal input to the time axis companding device is first input to the window function multiplier 11 and multiplied by the window function. As a result, the input audio signal is cut out in units of frames (S1). The frame unit audio signal is subjected to fast Fourier transform (FFT) in the FFT unit 12 to output frame unit frequency spectrum data including amplitude data and phase data (S2). Spectrum peak detecting unit 13 uses the peak detection algorithm to detect the local peaks of the envelope of the amplitude of the frequency spectrum output from the FFT unit 12 is output as the analysis frame AF _n (S3). The auditory psychological characteristic evaluation unit 20 compares the detected local peak with an auditory psychological characteristic curve stored in a table (not shown) to reduce local peak data (S4).
[0020]
Subsequently, in the frame controller 25, so that the number of frames corresponding to a desired draw ratio, thinning the analysis frame AF _n units, the repeating is performed (S5).
Next, the peak link unit 31 selects a peak in correspondence between the local peak data detected in the adjacent frames AF _n−1 and AF _{n and} links them to each other. That is, it is checked whether local peaks corresponding to the local peaks f1, f2, f3,... Of the past frame AF _n−1 also exist in the current frame AF _n. Corresponding local peaks f1 ', f2', f3 ', etc. are linked with local peaks f1, f2, f3, etc. (S6).
[0021]
Next, in the phase generation unit 32, the phase phase Φ _AFn− 1, _f at the linked local peak (frequency f) of the past analysis frame AF _n−1 , and the frequency f of the linked local peaks before and after, Based on f ′, the phase at the local peak of the corresponding composite frame SF _n is obtained (S7).
[0022]
Thus, when the amplitude and phase data of the synthesized frame SF _n is obtained, these data are subjected to inverse fast Fourier transform in the inverse FFT unit 41 to be converted into signals in the time domain. The signal for each frame converted into the time domain is superimposed in the window function multiplication and superposition unit 42 and output as an audio signal expanded in time.
[0023]
Although the embodiment has been described above, the present invention is not limited to this, and various modifications and additions can be made without departing from the spirit of the present invention.
For example, the method of peak detection in the analysis unit 10 is not limited to FFT, but may be other orthogonal transforms such as discrete cosine transform (DCT), as long as a local peak of each cut frame is detected.
Further, in the above-described embodiment, the time axis companding process in the time scaling unit 30 uses the data of the analysis frame AF _n as it is for the composite frame AF _n as the amplitude data. It may be obtained by interpolation of frame data.
[0024]
【The invention's effect】
As described above, according to the audio signal time axis companding apparatus, method, and program according to the present invention, it is possible to reduce the amount of data processing when performing data processing in the frequency domain and to perform real-time processing of the audio signal. Become.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of an audio signal time axis companding device according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram illustrating a method for reducing the amount of data using a minimum audible limit characteristic curve in the psychoacoustic characteristic evaluation unit 20;
FIG. 3 is a conceptual diagram illustrating a method for reducing the amount of data using a frequency masking characteristic curve in the psychoacoustic characteristic evaluation unit 20;
4 is a conceptual diagram for explaining a function of a peak cooperation unit 31 shown in FIG.
FIG. 5 is a flowchart showing the operation of the time-axis companding device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Analysis part, 11 ... Window function multiplication part, 12 ... FFT part, 13 ... Spectral peak detection part, 20 ... Auditory psychological characteristic evaluation part, 25 ... Frame number adjustment part , 30 ... Time scaling unit, 31 ... Peak cooperation unit, 32 ... Phase generation unit, 40 ... Synthesis unit, 41 ... Inverse FFT unit, 42 ... Window function superposition unit

Claims (5)

A detection unit that detects a plurality of local peaks of the amplitude envelope of the frequency spectrum from the audio signal separated in the frame, and outputs for each of said frames of amplitude data and phase data of the local peak as the analysis frame,
A data reducing unit that generates analysis frame deleting the human psychoacoustic characteristic curve and the amplitude data and phase data of small local peaks than該聴objective psychological characteristic curve is compared with the amplitude data of the analysis frame,
Wherein the number of frames per analysis frame unit time was adjusted based on a predetermined time scale modification ratio, adjacent obtained by a process of linking the local peak of the amplitude data and the analysis frame the adjusted analysis frame adjusted A time-axis companding device for audio signals, comprising: a synthesizing unit that synthesizes audio signals based on phase data calculated from the instantaneous frequency . The audio signal time axis companding apparatus according to claim 1, wherein the psychoacoustic characteristic curve is a minimum audible limit characteristic curve indicating a relationship between a minimum sound pressure and a frequency that can be heard by a human ear. 2. The audio signal time axis according to claim 1, wherein the auditory psychological characteristic curve is a frequency masking characteristic curve indicating a degree of difficulty in hearing a frequency in the vicinity of a frequency when a sound of a certain frequency is sensed by a human ear. Drawing machine. A time axis companding method of an audio signal by a time axis companding device that compands an original audio signal with a desired compression rate,
Detecting a plurality of local peaks of the amplitude envelope of the frequency spectrum from the audio signal divided into frames, and detecting the amplitude data and phase data of the local peaks for each frame as analysis frames ;
And data reduction step of generating an analysis frame deleting the amplitude data and phase data of small local peaks than該聴objective psychological characteristic curve is compared with the amplitude data of the analysis frame to human psychoacoustic characteristic curve,
Wherein the number of frames per analysis frame unit time was adjusted based on a predetermined time scale modification ratio, adjacent obtained by a process of linking the local peak of the amplitude data and the analysis frame the adjusted analysis frame adjusted And a synthesizing step for synthesizing the audio signal based on the phase data calculated from the instantaneous frequency . A detection step of detecting a plurality of local peaks of the amplitude envelope of the frequency spectrum from the audio signal separated in the frame, and outputs for each of said frames of amplitude data and phase data of the local peak as the analysis frame,
And data reduction step of generating an analysis frame deleting the amplitude data and phase data of small local peaks than該聴objective psychological characteristic curve is compared with the amplitude data of the analysis frame to human psychoacoustic characteristic curve,
Wherein the number of frames per analysis frame unit time was adjusted based on a predetermined time scale modification ratio, adjacent obtained by a process of linking the local peak of the amplitude data and the analysis frame the adjusted analysis frame adjusted An audio signal time axis companding program configured to cause a computer to execute a synthesis step of synthesizing an audio signal based on phase data calculated from the instantaneous frequency .

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