JP2012027255A - Band extension device, program, and voice communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a band extension device capable of suppressing unintended quality deterioration of a signal expanding a frequency band formed by utilizing a nonlinear processing.SOLUTION: The band extension device includes nonlinear processing means by which the nonlinear processing is applied to the signal in a narrow band of which the frequency band is limited. This device also includes whitening means which whitens the signal subjected to the nonlinear processing, or noise superimposition means by which a signal, which is formed by imparting to the white noise characteristics obtained by whitening the spectrum profile obtained by obtaining the spectrum profile of the signal having the expanded frequency band, is superimposed on the signal having the expanded frequency band.

Description

  The present invention relates to a band extension apparatus, a program, and a voice communication apparatus, and is applied to, for example, a case where a signal component exceeding the limit band is added to a telephone voice signal whose band is limited and converted to a wideband voice signal. To get.

  In many telephone systems that are voice communications, the frequency of voice signals that can be transmitted is limited to 4 kHz at most. This is a much narrower frequency range compared to the speech originally produced by humans, and therefore has poor quality. In order to solve such a problem, for example, as in the technique described in Patent Document 1, there is a technique for generating and adding a signal component exceeding a limited band to improve the quality.

  In the technique described in Patent Document 1, an audio signal with a limited band (hereinafter referred to as a narrowband signal or a narrowband audio signal) is subjected to LPC analysis, and an LPC coefficient representing a spectrum outline and a residual obtained by removing the spectrum outline are removed. The obtained LPC coefficients are broadened according to a predetermined conversion rule, the obtained residual signal is broadened by nonlinear processing, and the widened LPC coefficients and the widened residual signal are Then, a wideband voice signal is synthesized, and then a portion exceeding the limited band is extracted and added to the original narrowband signal, thereby widening the narrowband signal.

JP2009-223210A

  In general, the residual signal has a spectral outline whitened, and it can be said that the synthesis process using the LPC coefficient is a process of giving a predetermined spectral outline to the residual signal.

  In the technique described in Patent Document 1, for example, a relationship between an LPC coefficient for a narrowband signal and an LPC coefficient for a wideband signal whose bandwidth is not limited is obtained in advance. The LPC coefficient obtained by analyzing the narrowband signal is converted into the LPC coefficient having a wider band.

  On the other hand, the narrow band residual signal that has been whitened is widened by nonlinear processing, but the broadband residual signal that has been widened by nonlinear processing does not necessarily have a white spectral outline. For this reason, a wideband speech signal may be synthesized from a wideband LPC coefficient on the assumption that the spectral outline of the wideband residual signal is white and a wideband residual signal whose spectral outline is not white.

  Furthermore, even if the wideband residual signal is whitened, widening the LPC coefficient as described above does not necessarily provide a wideband LPC coefficient having a suitable correspondence with the narrowband LPC coefficient. A wideband speech signal synthesized by applying such a wideband LPC coefficient having an insufficient correspondence relationship may have an unintended spectral outline and may deteriorate in quality.

  The present invention has been made in view of the above-described problems, and a bandwidth expansion device and program that can suppress unintended quality degradation of a frequency band-enhanced signal generated using nonlinear processing, and An attempt is made to provide a voice communication device.

  According to a first aspect of the present invention, there is provided a band extending apparatus that has nonlinear processing means for performing nonlinear processing on a narrowband signal with a limited frequency band, and forms a signal with an expanded frequency band. A whitening means for whitening a signal subjected to nonlinear processing; and (b) obtaining a spectral outline of the signal with the expanded frequency band and flattening the obtained spectral outline with respect to white noise. It is characterized by comprising at least one of noise superimposing means for generating the given signal and superimposing it on the signal with the expanded frequency band.

  A second aspect of the present invention is a band expansion program for forming a signal having a frequency band expanded from a narrow band signal having a frequency band limited, wherein (1) the frequency band is limited to a computer. Non-linear processing is performed on the narrow-band signal to function as a non-linear processing means for forming a signal with an expanded frequency band, and (2) the computer is (2a) the signal subjected to the non-linear processing is white. And (2b) obtaining a spectral outline of the signal with the expanded frequency band, generating a signal in which white noise has a characteristic obtained by flattening the obtained spectral outline, and generating the frequency It is made to function as at least one of the noise superimposing means which superimposes on the signal by which the band was extended.

  According to a third aspect of the present invention, in a voice communication apparatus in which a band of a received voice signal is limited, the band extension apparatus of the first aspect of the invention is provided, and the band of the received voice signal is extended.

  According to the present invention, it is possible to suppress unintended quality deterioration of a signal with an expanded frequency band, which is generated using nonlinear processing.

It is a block diagram which shows the internal structure of the band expansion apparatus which concerns on 1st Embodiment. It is a block diagram which shows the principal part structure of the audio | voice communication apparatus which concerns on 1st Embodiment. It is a block diagram which shows the internal structure of the band expansion apparatus which concerns on 2nd Embodiment. It is a block diagram which shows the internal structure of the band extending apparatus which concerns on 3rd Embodiment. It is a block diagram which shows the internal structure of the band expansion apparatus which concerns on 4th Embodiment.

(A) First Embodiment Hereinafter, a first embodiment of a bandwidth extending apparatus and program and a voice communication apparatus according to the present invention will be described with reference to the drawings.

(A-1) Configuration of the First Embodiment FIG. 2 is a block diagram showing the main configuration of the voice communication apparatus according to the first embodiment.

  The voice communication apparatus 1 according to the first embodiment is, for example, an IP telephone apparatus (including a softphone), and includes a codec apparatus 2 that compresses and encodes a voice signal to be transmitted and decodes a received encoded voice signal. I have. The decoded speech signal output from the codec device 2 is a narrowband signal s (n), and is provided to the bandwidth extension device 3 of the first embodiment that extends the speech bandwidth to the high frequency side. When the voice communication device 1 of the first embodiment is a soft phone, the codec device 2 and the bandwidth extension device 3 are realized by a CPU and a program (codec program or bandwidth extension program) executed by the CPU. Is done.

  FIG. 1 is a block diagram showing an internal configuration of the bandwidth extension device 3 according to the first embodiment. Even if the bandwidth extension device 3 of the first embodiment is realized by a CPU and a bandwidth extension program (band extension program of the first embodiment) executed by the CPU, it is functionally Can be represented in FIG.

  In FIG. 1, the band extension device 3 of the first embodiment includes an upsampling circuit 101, an LPC analysis circuit 102, a residual nonlinear processing circuit 103, a whitening circuit 104, an LPC coefficient broadbanding circuit 105, an LPC synthesis circuit 106, A band-pass circuit 107 and an adder circuit 108 are included.

  In the band extension device 3, the narrowband signal s (n) output from the codec device 2 is given to the upsampling circuit 101 and the LPC analysis circuit 102. The narrowband signal s (n) output from the codec device 2 is a digital audio signal having a sampling frequency corresponding to a narrow band, and the sampling frequency is insufficient when viewed from a wideband after band expansion. .

  The upsampling circuit 101 increases the sampling frequency of the narrowband signal s (n) and outputs the upsampling signal su (n) to the adder circuit 108.

  The LPC analysis circuit 102 performs LPC analysis using the narrowband signal s (n), outputs the obtained LPC coefficient a to the LPC coefficient broadening circuit 105, and at the same time obtains a spectrum outline of the narrowband signal s (n). The residual signal e (n) from which the shape has been removed is output to the residual nonlinear processing circuit 103.

  The residual nonlinear processing circuit 103 increases the sampling frequency of the narrowband residual signal e (n), and then performs nonlinear processing such as full-wave rectification to obtain a wideband residual signal en (n). Are output to the whitening circuit 104. Non-linear processing performed by the residual non-linear processing circuit 103 is not limited to full-wave rectification, and non-linear processing in which components outside the limited band exceeding the limited band for the narrow-band signal s (n) such as half-wave rectification and clipping are generated. Any method may be used, and the method is not limited. Here, the wideband residual signal that has been widened by the non-linear processing of the residual non-linear processing circuit 103 does not necessarily have a white spectral outline.

  The whitening circuit 104 is a component that characterizes the band extending device 3 according to the first embodiment. The whitening circuit 104 is whitened when a broadband residual signal en (n) whose spectral outline is not white is input, and the broadband residual signal ew (n) whose spectral outline is white is input to the LPC synthesis circuit 106. Output. The whitening method by the whitening circuit 104 is not questioned. The whitening circuit 104 performs, for example, LPC analysis using the wideband residual signal en (n) output from the residual nonlinear processing circuit 103, and removes the spectral outline of the wideband residual signal en (n). A wideband residual signal ew (n) is output. By removing the spectral outline, the spectral outline is smoothed to become white. Further, for example, the whitening circuit 104 converts the spectral outline into a white spectral outline after performing conversion into a frequency domain signal by FFT, and then performing inverse FFT to obtain the spectral outline of the wideband residual signal e (n). Is removed (smoothed).

  The LPC coefficient broadening circuit 105 widens the narrowband LPC coefficient a and outputs the wideband LPC coefficient aw to the LPC synthesis circuit 106. The method for widening the LPC coefficient is not limited. The method described in Patent Document 1 described above can be applied. In addition, the methods described in JP2010-55000, JP2010-55002, and JP11-126098 can be applied.

  The LPC synthesis circuit 106 performs LPC synthesis processing from the wideband residual signal ew (n) from the whitening circuit 104 and the wideband LPC coefficient aw from the LPC coefficient widening circuit 105, and generates the synthesized wideband signal sr (n). Obtained and output to the band-pass circuit 107.

  The band pass circuit 107 passes the band portion other than the limited band for the narrow band signal s (n) with respect to the combined wide band signal sr (n), and outputs the band pass signal sb (n) to the adder circuit 108. To do. The band pass signal sb (n) is a signal in a band that the narrow band signal s (n) does not have, in other words, an extended band signal.

  The adder circuit 108 uses the upsampling signal (same as a narrowband signal in band) su (n) output from the upsampling circuit 101 and the extended band signal sb (n) output from the bandpass circuit 107. Addition is performed to obtain a wideband signal sw (n) and output as an output signal from the band extension device 3.

(A-2) Operation of the First Embodiment Next, the operation of the bandwidth expansion device 3 of the first embodiment will be described in detail with reference to the drawings. In addition, description of operation | movement of the audio | voice communication apparatus 1 of 1st Embodiment is abbreviate | omitted.

  The narrowband signal s (n) output from the codec device 2 is supplied to the upsampling circuit 101 and the LPC analysis circuit 102.

  The sampling frequency of the narrowband signal s (n) is increased in the upsampling circuit 101, and the increased upsampling signal su (n) is output to the adder circuit.

  LPC analysis is performed on the narrowband signal s (n) by the LPC analysis circuit 102, and the obtained LPC coefficient a is output to the LPC coefficient broadbanding circuit 105, and the residual signal e (n) is the residual. It is output to the nonlinear processing circuit 103. The sampling frequency of the residual signal e (n) in the narrow band is increased in the residual nonlinear processing circuit 103 and is subjected to nonlinear processing to be widened, and the residual signal en (n) that has become wideband is white. Is output to the conversion circuit 104. The wideband residual signal en (n) is whitened in the whitening circuit 104 and the whitened wideband residual signal ew (n) is output to the LPC synthesis circuit 106. The narrowband LPC coefficient a is widened by the LPC coefficient widening circuit 105, and the wideband LPC coefficient aw is output to the LPC synthesis circuit 106. The wideband residual signal ew (n) from the whitening circuit 104 and the wideband LPC coefficient aw from the LPC coefficient widening circuit 105 are given to the LPC synthesis circuit 106, and LPC synthesis processing is performed, and the resulting synthesis is obtained. The broadband signal sr (n) is output to the band pass circuit 107.

  The combined wideband signal sr (n) is filtered by the bandpass circuit 107 into a band portion other than the limited band for the narrowband signal s (n), and the bandpass signal sb (n) is output to the adder circuit 108.

  The upsampling signal output from the upsampling circuit 101 and the extended band signal sb (n) output from the bandpass circuit 107 are added by the adder circuit 108, and the obtained wideband signal sw (n) is added to the band extension. It is output to the next stage device of the device 3.

(A-3) Effect of the First Embodiment According to the first embodiment, the residual signal after nonlinear processing is whitened, so that a broadband signal generated by LPC synthesis is not intended for an approximate spectrum. There are fewer cases with shapes, and deterioration of sound quality can be suppressed.

(B) Second Embodiment Next, a second embodiment of the bandwidth extending apparatus and program and the voice communication apparatus according to the present invention will be described with reference to the drawings.

(B-1) Configuration of the Second Embodiment The configuration of the voice communication apparatus of the second embodiment is the same as that of the first embodiment, and the configuration of the bandwidth extension apparatus of the second embodiment will be described below. To do.

  FIG. 3 is a block diagram showing an internal configuration of the bandwidth extension device 3A according to the second embodiment. Even if the bandwidth extension device 3A of the second embodiment is realized by a CPU and a bandwidth extension program (band extension program of the second embodiment) executed by the CPU, it is functionally Can be represented in FIG. In FIG. 3, the same and corresponding parts as those in FIG. 1 according to the first embodiment are denoted by the same reference numerals.

  In FIG. 3, the band extending apparatus 3A of the second embodiment includes an upsampling circuit 101, an LPC analysis circuit 102, a residual nonlinear processing circuit 103, an LPC coefficient broadband circuit 105, an LPC synthesis circuit 106, a band pass circuit 107, An adder circuit 108 and a white noise superimposing unit 200 are included. The white superimposing unit 200 includes a voiced / voiceless determination circuit 201, a wideband LPC analysis circuit 202, a white noise generation circuit 203, an LPC noise synthesis circuit 204, and an addition circuit 205.

  The upsampling circuit 101, the LPC analysis circuit 102, the residual nonlinear processing circuit 103, the LPC coefficient widening circuit 105, the LPC synthesis circuit 106, the band pass circuit 107, and the addition circuit 108 function in the same manner as in the first embodiment. It is.

  The band extension device 3A of the second embodiment includes a white color superimposing unit 200 instead of the whitening circuit 104 of the first embodiment. Since the whitening circuit 104 is omitted, the wideband residual signal en (n) output from the residual nonlinear processing circuit 103 is output to the LPC synthesis circuit 106, and the LPC synthesis circuit 106 LPC synthesis processing is performed using the signal en (n) and the wideband LPC coefficient aw from the LPC coefficient wideband circuit 105. Therefore, the synthesized broadband signal sr (n) output from the LPC synthesis circuit 106 is more likely to have an unintended spectral shape than in the first embodiment.

  The white color superimposing unit 200 attempts to make an unintended frequency component in the synthesized wideband signal sr (n) inconspicuous by superimposing the white signal on the synthesized wideband signal sr (n) from the LPC synthesis circuit 106. . In other words, a noise signal with a similar spectral outline is superimposed on a wideband signal generated from a narrowband signal, making it difficult to detect audible noise due to an unintended spectral outline and suppressing deterioration in sound quality. It is what.

  The narrowband signal s (n) is input to the voiced / unvoiced determination circuit 201 in the white color superimposing unit 200. The voiced / unvoiced determination circuit 201 determines whether it is voiced sound or unvoiced sound using the narrowband signal s (n), and outputs the voiced / unvoiced determination result v to the white noise generating circuit 203. The voiced / unvoiced determination circuit 201 outputs v = 1 for voiced sound and v = 0 for unvoiced sound. Any method may be applied as the voiced / unvoiced determination method in the voiced / unvoiced determination circuit 201. For example, a method of monitoring the periodicity of the narrowband signal s (n) and determining a voiced sound when the periodicity is strong can be applied.

  The broadband LPC analysis circuit 202 performs LPC analysis using the synthesized broadband signal sr (n), outputs the synthesized broadband LPC coefficient w to the LPC noise synthesis circuit 204, and at the same time, approximates the spectrum of the synthesized broadband signal sr (n). Is output to the white noise generation circuit 203.

  The white noise generation circuit 203 generates white noise having the same power as that of the combined wideband residual signal se (n), and generates a white noise signal p (n) obtained by multiplying the generated white noise by a gain α that defines the degree of superposition. This is output to the noise synthesis circuit 204. The gain α takes a value corresponding to the voiced / unvoiced determination result v, and takes a value shown in the equation (1), for example. Equation (1) is such that α = β (where 0 <β <1) when v = 1 (voiced sound), and α = 1 when v = 0 (unvoiced sound). That is, the degree of superimposition of white noise is increased in the case of unvoiced sound (unvoiced sound section) than in voiced sound (voiced sound section). The voiced / unvoiced determination result v may be not a binary value but a multi-value (three or more values) that changes stepwise according to the degree of periodicity.

α = β + (1-β) × (1-v) (1)
The LPC noise synthesis circuit 204 flattens the spectral outline to some extent by, for example, multiplying the synthesized wideband LPC coefficient w by a leak coefficient, and then generates a synthesized white noise signal ps (n) of the white noise signal p (n). This is output to the adder circuit 205.

  The adding circuit 205 adds the combined wideband signal sr (n) output from the LPC combining circuit 106 and the combined white noise signal ps (n) output from the LPC noise combining circuit 204 and outputs the result to the bandpass circuit 106. Is.

(B-2) Operation of Second Embodiment Next, the operation of the bandwidth expansion device 3A of the second embodiment will be described in detail with reference to the drawings.

  The narrowband signal s (n) output from the codec device 2 is supplied to the upsampling circuit 101, the LPC analysis circuit 102, and the voiced / unvoiced determination circuit 201.

  The sampling frequency of the narrowband signal s (n) is increased in the upsampling circuit 101, and the increased upsampling signal su (n) is output to the adder circuit.

  LPC analysis is performed on the narrowband signal s (n) by the LPC analysis circuit 102, and the obtained LPC coefficient a is output to the LPC coefficient broadbanding circuit 105, and the residual signal e (n) is the residual. It is output to the nonlinear processing circuit 103. The sampling signal of the narrowband residual signal e (n) is increased in the residual non-linear processing circuit 103 and is subjected to non-linear processing to be widened, and the residual signal en (n) having a wide band is converted to LPC. It is output to the synthesis circuit 106. The narrowband LPC coefficient a is widened by the LPC coefficient widening circuit 105, and the wideband LPC coefficient aw is output to the LPC synthesis circuit 106. The wideband residual signal en (n) from the residual nonlinear processing circuit 103 and the wideband LPC coefficient aw from the LPC coefficient widening circuit 105 are given to the LPC synthesis circuit 106, and the LPC synthesis process is performed and obtained. The combined broadband signal sr (n) is output to the broadband LPC analysis circuit 202 and the addition circuit 205.

  Also, the voiced / voiceless determination circuit 201 determines whether the narrowband signal s (n) is voiced or unvoiced, and the voiced / voiceless determination result v is output to the white noise generation circuit 203. The synthesized broadband signal sr (n) output from the LPC synthesis circuit 106 is subjected to LPC analysis in the broadband LPC analysis circuit 202, and the resultant synthesized broadband LPC coefficient w is output to the LPC noise synthesis circuit 204 and obtained. The combined wideband residual signal se (n) is output to the white noise generation circuit 203. The white noise generation circuit 203 generates white noise having the same power as the combined wideband residual signal se (n), and multiplies the generated white noise by a gain α that takes a value corresponding to the voiced / unvoiced determination result v. The obtained white noise signal p (n) is output to the LPC noise synthesis circuit 204. The synthesized wideband LPC coefficient w is multiplied by the leak coefficient in the LPC noise synthesis circuit 204 and the spectral outline is flattened to some extent, and the LPC noise synthesis circuit 204 is obtained from the flattened LPC coefficient and the white noise signal p (n). As a result, a composite white noise signal ps (n) is generated and output to the adder circuit 205. The combined wideband signal sr (n) output from the LPC combining circuit 106 and the combined white noise signal ps (n) output from the LPC noise combining circuit 204 are added by the adding circuit 205 and output to the bandpass circuit 106. .

  The addition signal sr (n) + ps (n) is filtered by the band pass circuit 107 to a band portion other than the limited band for the narrow band signal s (n), and the band pass signal sb (n) is added to the adder circuit 108. Is output.

  The upsampling signal output from the upsampling circuit 101 and the extended band signal sb (n) output from the bandpass circuit 107 are added by the adder circuit 108, and the obtained wideband signal sw (n) is added to the band extension. It is output to the next stage device of the device 3A.

(B-3) Effect of Second Embodiment According to the second embodiment, a noise signal having a similar spectral outline is superimposed on a wideband signal generated from a narrowband signal. It is possible to make it difficult to detect audible noise due to an unintended spectral outline, and to suppress deterioration in sound quality. Furthermore, according to the second embodiment, since the added amount of noise is controlled according to the characteristics of the narrowband signal that is the source of expansion, it is possible to more effectively suppress deterioration in sound quality.

(C) Third Embodiment Next, a third embodiment of the bandwidth extending apparatus and program and the voice communication apparatus according to the present invention will be described with reference to the drawings.

  In the third embodiment, the configuration of the voice communication apparatus is the same as that of the first embodiment, and the configuration of the band extending apparatus of the third embodiment will be described below.

  FIG. 4 is a block diagram illustrating an internal configuration of the bandwidth expansion device 3B according to the third embodiment. Even if the bandwidth extension device 3B of the third embodiment is realized by a CPU and a bandwidth extension program (a bandwidth extension program of the third embodiment) executed by the CPU, it is functionally Can be represented in FIG. In FIG. 4, the same and corresponding parts as those in FIG. 1 according to the first embodiment and FIG. 3 according to the second embodiment are denoted by the same reference numerals.

  In FIG. 4, the band extending apparatus 3B of the third embodiment includes an upsampling circuit 101, an LPC analysis circuit 102, a residual nonlinear processing circuit 103, a whitening circuit 104, an LPC coefficient broadbanding circuit 105, an LPC synthesis circuit 106, A band-pass circuit 107, an adder circuit 108, and a white noise superimposing unit 200 are included. Similar to the second embodiment, the white noise superimposing unit 200 includes a voiced / unvoiced determination circuit 201, a broadband LPC analysis circuit 202, a white noise generation circuit 203, an LPC noise synthesis circuit 204, and an addition circuit 205.

  As is clear from the comparison between FIG. 3 and FIG. 4, the bandwidth expansion device 3B of the third embodiment is obtained by adding a whitening circuit 104 to the configuration of the bandwidth expansion device 3A of the second embodiment. . From another point of view, as is clear from the comparison between FIG. 1 and FIG. 4, the band extending apparatus 3B according to the third embodiment includes a white noise superimposing unit in the configuration of the band extending apparatus 3 according to the first embodiment. 200 is added.

  The whitening circuit 104 whitens the wideband residual signal en (n), and the whitened wideband residual signal ew (n) is used for LPC synthesis by the LPC synthesis circuit 106. Therefore, even if the wideband residual signal en (n) is whitened, an unintended frequency component is generated in the spectral outline of the synthesized wideband signal sr (n) from the LPC synthesis circuit 106 due to compatibility with the wideband LPC coefficient aw and the like. There is a fear.

  In the third embodiment, white noise is generated so that even if an unintended frequency component occurs in the result of LPC synthesis using the whitened wideband residual signal ew (n), it does not become a problem. The superimposing process by the superimposing unit 200 is performed.

  According to the third embodiment, the effects of the first embodiment and the effects of the second embodiment are synergized, and deterioration of sound quality can be more effectively suppressed.

(D) Fourth Embodiment Next, a fourth embodiment of the bandwidth extending apparatus and program and the voice communication apparatus according to the present invention will be described with reference to the drawings.

  In the fourth embodiment, the configuration of the voice communication apparatus is the same as that of the first embodiment, and the configuration of the band extending apparatus of the fourth embodiment will be described below.

  FIG. 5 is a block diagram illustrating an internal configuration of a bandwidth expansion device 3C according to the fourth embodiment. Even if the bandwidth extension device 3C of the fourth embodiment is realized by a CPU and a bandwidth extension program (band extension program of the fourth embodiment) executed by the CPU, it is functionally Can be represented in FIG. In FIG. 5, the same reference numerals are given to the same and corresponding parts as in FIG. 3 according to the second embodiment described above.

  In FIG. 5, the band extending apparatus 3 </ b> C of the fourth embodiment includes an upsampling circuit 101, a speech nonlinear processing circuit 300, a band pass circuit 107, an adder circuit 108, and a white noise superimposing unit 200. Similar to the second embodiment, the white noise superimposing unit 200 includes a voiced / unvoiced determination circuit 201, a broadband LPC analysis circuit 202, a white noise generation circuit 203, an LPC noise synthesis circuit 204, and an addition circuit 205.

  In the first to third embodiments described above, LPC analysis is performed on the narrowband signal s (n) to obtain vocal tract information (LPC coefficient) and vocal cord signal (residual signal), Each of the signals was broadened, and then subjected to LPC synthesis to obtain a wideband signal sr (n).

  This fourth embodiment employs a configuration that converts a narrowband signal s (n) into a wideband signal sr (n) without dividing it into vocal tract information (LPC coefficient) and vocal cord signal (residual signal). ing. Such a component is a speech nonlinear processing circuit 300.

  The speech nonlinear processing circuit 300 increases the sampling frequency of the narrowband signal s (n) and then performs nonlinear processing such as full-wave rectification to obtain a broadband signal sr (n). The nonlinear processing performed by the speech nonlinear processing circuit 300 is not limited to full-wave rectification, but is nonlinear processing in which components outside the limited band exceeding the limited band for the narrowband signal s (n) such as half-wave rectification and clipping are generated. Any method may be used, and the method is not limited. Note that an output signal from the upsampling circuit 101 may be used as an input signal to the speech nonlinear processing circuit 300, and an increase in sampling frequency in the speech nonlinear processing circuit 300 may be omitted.

  Here, the broadband signal sr (n) output from the speech nonlinear processing circuit 300 does not necessarily have an intended shape of the spectrum. Therefore, in the fourth embodiment, superimposition processing by the white noise superimposing unit 200 is performed.

  According to the fourth embodiment, a method of generating a wideband signal from a narrowband signal without dividing the narrowband signal into vocal tract information (LPC coefficient) and vocal cord signal (residual signal) The same effects as those of the second embodiment described above can be obtained.

  Incidentally, the wideband processing of the LPC coefficient does not necessarily provide a suitable wideband LPC coefficient, and the wideband processing of the LPC coefficient itself may give an unintended spectrum outline. Rather, the sound quality is less degraded when the LPC analysis and synthesis processing are not performed. The fourth embodiment is adapted to such a situation.

(E) Other Embodiments In each of the above embodiments, the voice communication device provided with the bandwidth expansion device of any of the embodiments has been described. However, the voice communication device is the bandwidth expansion device of the first to fourth embodiments. 2 or more of the bandwidth expansion devices may be provided so that the user can select which bandwidth expansion device to apply.

  In this case, the plurality of bandwidth extension devices mounted on the same voice communication device are configured to use the same components in common, and depending on the selection of a selection switch appropriately provided on the signal path, It may be possible to function as such a bandwidth expansion device.

  In the first to third embodiments, an example of applying the LPC analysis as the vocal tract analysis method is shown, but other vocal tract analysis methods may be applied.

  In the fourth embodiment, the white noise superimposing unit 200 is provided after the speech nonlinear processing circuit 300. However, the white noise circuit similar to that of the first embodiment is used instead of the white noise superimposing unit 200. May be provided after the speech nonlinear processing circuit 300.

  In the above description, the IP telephone device has been described as an example of the voice communication device using the bandwidth expansion device of each of the above embodiments. However, the use of the bandwidth expansion device is not limited to this. The present invention may be applied to a bandwidth expansion device mounted on a voice communication device such as a VoIP gateway or a VoIP server.

  DESCRIPTION OF SYMBOLS 1 ... Voice communication apparatus, 3, 3A-3C ... Band expansion apparatus, 101 ... Upsampling circuit, 102 ... LPC analysis circuit, 103 ... Residual nonlinear processing circuit, 104 ... Whitening circuit, 105 ... LPC coefficient widening circuit, DESCRIPTION OF SYMBOLS 106 ... LPC synthesis circuit, 107 ... Band pass circuit, 108 ... Addition circuit, 200 ... White superimposition part, 201 ... Voiced / unvoiced determination circuit, 202 ... Broadband LPC analysis circuit, 203 ... White noise generation circuit, 204 ... LPC noise synthesis circuit 205 ... Adder circuit, 300 ... Audio nonlinear processing circuit.

Claims (5)

In a band extending apparatus that has nonlinear processing means for performing nonlinear processing on a narrowband signal with a limited frequency band, and forms a signal with an expanded frequency band,
Whitening means for whitening the signal subjected to the nonlinear processing;
Noise obtained by obtaining a spectral outline of a signal with the above frequency band extended, generating a signal with white noise added to a characteristic obtained by flattening the obtained spectral outline, and superimposing it on the signal with the above frequency band extended A band extending apparatus comprising at least one of superimposing means.   2. The band extending apparatus according to claim 1, wherein the nonlinear processing means performs nonlinear processing on a signal obtained by removing a spectrum outline from a signal to be expanded in a frequency band.   The band extending apparatus according to claim 1, further comprising: the noise superimposing unit, wherein the noise superimposing unit changes a superimposition amount according to a periodicity characteristic of a signal to be expanded in a frequency band. A bandwidth extension program for forming a narrow band signal with a limited frequency band and a signal with an extended frequency band,
The computer functions as a non-linear processing means that performs non-linear processing on a narrow-band signal with a limited frequency band to form a signal with an expanded frequency band,
The computer obtains the whitening means for whitening the signal subjected to the above nonlinear processing and the spectral outline of the signal with the expanded frequency band, and the flattened characteristic of the obtained spectral outline for white noise. A band expansion program that generates a signal given in the above and functions as at least one of noise superimposing means that superimposes the signal on the signal with the expanded frequency band. In a voice communication device where the band of the received voice signal is limited,
An audio communication apparatus comprising the band extending apparatus according to any one of claims 1 to 3 and extending a band of a received audio signal.

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