JP2007171339A - Audio signal processing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal processing unit capable of faithfully generating audio signal to original sound, by accurately generating harmonic components from the original audio signal. <P>SOLUTION: This audio signal processing unit has a mixing section 21 which squares the audio signal, a high-pass filter 22 which attenuates the audible band components of the signal generated by the mixing section 21, and an addition section 11 which adds a signal that has passed through the high-pass filter 22 to the audio signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an audio signal processing apparatus.

  A technique has been proposed for adding a component in a band other than the limited band to an audio signal band-limited to an audible band or the like so as to approach the original sound (see, for example, Patent Document 1).

  FIG. 6 is a block diagram showing an example of a conventional audio signal processing apparatus. This conventional audio signal processing apparatus adds frequency components other than the limited band to the audio signal band-limited to the audible band.

  In the apparatus shown in FIG. 6, the harmonic component generation unit 101 generates a harmonic component from the audio signal. On the other hand, the delay unit 102 delays the audio signal by the time required for generating the harmonic component by the harmonic component generating unit 101.

  Then, the generated overtone component is added to the audio signal by the adding unit 111. The audio signal to which the harmonic component is added by the adding unit 111 is output through the low-pass filter 112. Since the energy in the entire band of the audio signal increases as the harmonic component is added, the low-pass filter 112 attenuates unnecessary high-frequency components and suppresses an increase in energy in the entire band of the audio signal.

  In this way, a harmonic component is added to the input audio signal, and an audio signal with the harmonic component added is output.

  In the overtone component generation unit 101 that generates overtone components, the signal generation unit 121 generates a signal having a certain frequency distribution, and the mixing unit 122 converts the signal generated by the signal generation unit 121 into an input audio signal. Mix. That is, the mixing unit 122 calculates the product of the signal generated by the signal generation unit 121 and the input audio signal, and outputs a signal of the calculation result. The high-pass filter 123 transmits the harmonic component in the signal generated by the mixing unit 122 and attenuates the frequency component below the audible band.

  As a result, the harmonic component generation unit 101 generates a harmonic component based on the input audio signal.

Japanese Patent Laid-Open No. 2-311006 (FIG. 1 etc.)

  However, in the conventional audio signal processing apparatus, since the harmonic component generation unit 101 mixes the signal with a constant frequency distribution by the signal generation unit 121 with the input audio signal, the generated harmonic component is input. In addition, the frequency component is not twice the frequency component of each audio signal.

  That is, assuming that the audible band of the audio signal is fL to fH and the frequency of the signal by the signal generation unit 121 is fa, the frequency band of the mixed signal corresponding to a certain frequency f is (fL + fa) to (fH + fa). Therefore, it is difficult to generate a frequency component twice as high as any frequency component in the audible band fL to fH of the audio signal.

  For this reason, an accurate harmonic component cannot be obtained, and the processed audio signal may not be faithful to the original sound.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an audio signal processing apparatus capable of accurately generating a harmonic component from an original audio signal and generating an audio signal faithful to the original sound. .

  In order to solve the above problems, the present invention is configured as follows.

  One of the audio signal processing apparatuses according to the present invention is a first multiplication unit that squares an audio signal, and a first component that attenuates a band component equal to or lower than the upper limit frequency of the audio signal among signals generated by the first multiplication unit. 1 high-pass filter and an adding means for adding the signal after passing through the first high-pass filter to the audio signal.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in this case, the audio signal processing apparatus has a second multiplication unit that multiplies the signal generated by the first multiplication unit by the audio signal, and an upper limit of the audio signal among the signals generated by the second multiplication unit. A second high-pass filter that attenuates a frequency component that is twice or less the frequency. The adding means adds the signal after passing through the first high-pass filter and the signal after passing through the second high-pass filter to the audio signal.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in this case, the audio signal processing apparatus has a third multiplication unit that multiplies the signal generated by the second multiplication unit by the audio signal, and an upper limit of the audio signal among the signals generated by the third multiplication unit. And a third high-pass filter that attenuates a frequency component equal to or less than three times the frequency. The adding means adds the signal after passing through the first high-pass filter, the signal after passing through the second high-pass filter, and the signal after passing through the third high-pass filter to the audio signal.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in this case, the audio signal processing apparatus includes a fourth multiplication unit that multiplies the signal generated by the third multiplication unit by the audio signal, and an upper limit of the audio signal among the signals generated by the fourth multiplication unit. And a fourth high-pass filter that attenuates a frequency component that is four times or less the frequency. The adding means passes the signal after passing through the first high-pass filter, the signal after passing through the second high-pass filter, the signal after passing through the third high-pass filter, and the fourth high-pass filter. The later signal is added to the audio signal.

  Also, one of the audio signal processing apparatuses according to the present invention raises an audio signal to the 2nd to Nth power (N is an integer equal to or greater than 2), from a signal in the second harmonic band to a signal in the N harmonic band (N−1). ) Signal overtone generation means, and addition means for adding (N−1) signals generated by the overtone generation means to the audio signal.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in that case, the audio signal processing apparatus includes a front-stage high-pass filter having a filter frequency within the frequency band of the audio signal. Then, the harmonic generation means raises the signal that has passed through the preceding high-pass filter to the 2nd to Nth power (N is an integer of 2 or more), and (N−1) number of signals from the second harmonic band signal to the N harmonic band signal. A signal is generated, and the adding means adds (N-1) signals generated by the harmonic overtone generating means to the audio signal.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in that case, the front-stage high-pass filter has a filter frequency that is equal to or lower than half of the upper limit frequency of the audio signal.

  The audio signal processing apparatus according to the present invention may be configured as follows in addition to any of the above audio signal processing apparatuses. That is, in that case, the harmonic generation means, for each of one or a plurality of signals from the signal of the second harmonic band to the signal of the N harmonic band, before the computation of the 2nd to Nth powers of the audio signal, One or more pre-stage high-pass filters having a filter frequency in the frequency band are included.

  In addition to the audio signal processing apparatus described above, the audio signal processing apparatus according to the present invention may be configured as follows. That is, in this case, the front-stage high-pass filter has a filter frequency corresponding to the corresponding harmonic band.

  The audio signal processing apparatus according to the present invention may be configured as follows in addition to any of the above audio signal processing apparatuses. In other words, in this case, the harmonic overtone generation unit includes one or a plurality of amplification units that amplify one or a plurality of signals in the second harmonic band signal to the N harmonic band signal.

  ADVANTAGE OF THE INVENTION According to this invention, the audio signal processing apparatus which can produce | generate an overtone component correctly from the original audio signal and can produce | generate an audio signal faithful to an original sound can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 1 of the present invention. In FIG. 1, the delay unit 1 delays the input audio signal by the time required for calculation in the high frequency generation units 2, 3, 4, and 5.

  The high frequency generator 2 generates a second harmonic component of the input audio signal. In the high frequency generator 2, the mixing unit 21 calculates the product of the input audio signal and the same input audio signal. The high-pass filter (hereinafter referred to as HPF) 22 is a filter having a filter frequency set near the upper limit frequency fH of the audible band. The filter frequency of the HPF 22 may be any frequency that is not less than the upper limit frequency fHa of the input audio signal and less than (2 × fHa). For example, in the case of telephone voice, the upper limit frequency fHa of the audio signal is about 4 kHz, and the filter frequency of the HPF 22 is any frequency from 4 kHz to 8 kHz. The delay unit 23 delays the output signal of the high frequency generator 2 so as to be synchronized with the output signal of the high frequency generator 5. That is, the output signal of the high frequency generator 2 and the output signal of the high frequency generator 5 generated based on the audio signal at time t are output at the same timing.

  The high frequency generator 3 generates a third harmonic component of the input audio signal. In the high frequency generator 3, the delay unit 31 delays the input audio signal by the time required for the calculation of the mixing unit 21. The mixing unit 32 calculates the product of the signal generated by the calculation of the mixing unit 21 and the input audio signal. The HPF 33 is a filter having a filter frequency set in the vicinity of a frequency (2 × fH) that is twice the upper limit frequency fH of the audible band. The filter frequency of the HPF 33 may be any frequency not lower than (2 × fHa) and lower than (3 × fHa). For example, in the case of telephone voice, the upper limit frequency fHa of the audio signal is about 4 kHz, and the filter frequency of the HPF 33 is any frequency from 8 kHz to 12 kHz. The delay unit 34 delays the output signal of the high frequency generation unit 3 so as to be synchronized with the output signal of the high frequency generation unit 5. That is, the output signal of the high frequency generator 3 and the output signal of the high frequency generator 5 generated based on the audio signal at time t are output at the same timing.

  The high frequency generator 4 generates a fourth harmonic component of the input audio signal. In the high frequency generation unit 4, the delay unit 41 delays the input audio signal by the time required for calculation by the mixing unit 21 and the mixing unit 32. The mixing unit 42 calculates the product of the signal generated by the calculation of the mixing unit 32 and the input audio signal. The HPF 43 is a filter having a filter frequency set in the vicinity of a frequency (3 × fH) that is three times the upper limit frequency fH of the audible band. The filter frequency of the HPF 43 may be any frequency not lower than (3 × fHa) and lower than (4 × fHa). For example, in the case of telephone voice, the upper limit frequency fHa of the audio signal is about 4 kHz, and the filter frequency of the HPF 43 is any one of 12 kHz to 16 kHz. The delay unit 44 delays the output signal of the high frequency generation unit 4 so as to be synchronized with the output signal of the high frequency generation unit 5. That is, the output signal of the high frequency generator 4 and the output signal of the high frequency generator 5 generated based on the audio signal at time t are output at the same timing.

  In addition, the high frequency generator 5 generates a fifth harmonic component of the input audio signal. In the high frequency generation unit 5, the delay unit 51 delays the input audio signal by the time required for calculation by the mixing unit 21, the mixing unit 32, and the mixing unit 42. The mixing unit 52 calculates the product of the signal generated by the calculation of the mixing unit 42 and the input audio signal. The HPF 53 is a filter having a filter frequency set in the vicinity of a frequency (4 × fH) that is four times the upper limit frequency fH of the audible band. The filter frequency of the HPF 53 may be any frequency not lower than (4 × fHa) and lower than (5 × fHa). For example, in the case of telephone voice, the upper limit frequency fHa of the audio signal is about 4 kHz, and the filter frequency of the HPF 53 is any one of 16 kHz to 20 kHz.

  The adder 11 adds the second harmonic component signal from the high frequency generator 2, the third harmonic component signal from the high frequency generator 3, and the fourth harmonic component from the high frequency generator 4 to the input audio signal delayed by the delay unit 1. The signal and the signal of the fifth harmonic component from the high frequency generator 5 are added.

  The low-pass filter (hereinafter referred to as LPF) 12 is a filter that reduces the power of the audio signal after overtone addition. Since the power of the audio signal increases with the addition of the second harmonic component to the fifth harmonic component, the LPF 12 reduces the power of the audio signal after adding the harmonic.

  As described above, each of the high-frequency generation units 2, 3, and 4 that generate harmonic components other than the maximum order is provided with delay units 23, 34, and 44 that delay the output signal. Each of the high-frequency generation units 3, 4, 5 to be generated is provided with delay units 31, 41, 51 for delaying an input signal.

  The high frequency generators 2, 3, 4, and 5 are provided with mixing units 21, 32, 42, and 52 and HPFs 22, 33, 43, and 53, respectively. In the high frequency generators 2, 3, 4, and 5 that generate the i harmonic component (i = 2, 3, 4, and 5), the mixing units 21, 32, 42, and 52 are connected to the input audio signal (when i = 2). ) Or (i-1) The product of the output signals of the mixing units 21, 32, 42, and 52 of the high frequency generation units 2, 3, and 4 that generate harmonic components and the input audio signal is calculated. The HPFs 22, 33, 43, and 53 have a filter frequency in the vicinity of (i × fH) in the high-frequency generation units 2, 3, 4, and 5 that generate i harmonic components (i = 2, 3, 4, and 5). Note that the filter frequencies of the HPFs 22, 33, 43, and 53 are set so that the frequency bands of signals passing through the HPFs 22, 33, 43, and 53 are continuous.

  In the first embodiment, each harmonic component from the second harmonic component to the fifth harmonic component is generated. However, only the second harmonic component or only the second harmonic component to the N harmonic component (N is 2 or more and other than 5). Each harmonic component up to (integer) may be generated.

  The audio signal according to the present embodiment is a digital audio signal whose frequency component is limited to an audible band, and the digital audio signal is a PCM (Pulse Code Modulation) signal, but other band-limited audio. It may be a signal, for example a telephone voice or a compressed audio signal.

  When this audio signal processing device is realized by a microcomputer or a digital signal processor, the mixing units 21, 32, 42, 52, HPFs 22, 33, 43, 53, the adding unit 11 and the LPF 12 are connected to the CPU, MPU according to the program. The delay unit 1, 23, 31, 34, 41, 44, 51 is realized by storing each delay time in a memory or the like in a microcomputer or a digital signal processor. The

  When the audio signal processing device is realized by a dedicated circuit, that is, a hard wire, the mixing units 21, 32, 42, and 52 are used as a mixer, the HPFs 22, 33, 43, and 53 and the LPF 12 are used as digital filters, and an adding unit. 11 is realized as an adder, and the delay units 1, 23, 31, 34, 41, 44, and 51 are realized as delay elements.

  Next, the operation of the above apparatus will be described. FIG. 2 is a diagram illustrating a correspondence relationship between the frequency band of the second to fifth harmonic components generated in the first embodiment and the frequency band of the original audio signal.

  When an audio signal is input, an audio signal at a certain time is supplied to the delay unit 1, the high frequency generation unit 2, the high frequency generation unit 3, the high frequency generation unit 4, and the high frequency generation unit 5.

  In the high frequency generation unit 2, the mixing unit 21 squares the value of the audio signal at that time. Thereby, the output signal of the mixing unit 21 includes a frequency component that is twice the frequency component of the audio signal. 2 is attenuated by the HPF 22 in the output signal of the mixing unit 21 and the second harmonic band component shown in FIG. 2 passes through the HPF 22. The signal that has passed through the HPF 22 is supplied to the adder 11 after being delayed by the delay unit 23 for a predetermined time.

  In the high frequency generation unit 3, the delay unit 31 delays the audio signal at that time by the calculation time of the mixing unit 21 and then supplies the delayed audio signal to the mixing unit 32. The mixing unit 31 calculates the product of the value obtained by squaring the value of the audio signal at the same time by the mixing unit 21 and the value of the audio signal at the same time. For this reason, the value obtained by raising the value of the audio signal at the same time to the third power is output from the mixing unit 32. Thus, the output signal of the mixing unit 32 includes a frequency component that is three times the frequency component of the audio signal. Then, a frequency component equal to or lower than twice the upper limit frequency fH of the audible band in the output signal of the mixing unit 32 is attenuated by the HPF 33, and the component of the third harmonic band shown in FIG. 2 passes through the HPF 33. The signal that has passed through the HPF 33 is supplied to the adder 11 after being delayed by a delay unit 34 for a predetermined time.

  In the high frequency generator 4, the delay unit 41 delays the audio signal at that time by the calculation time of the mixing unit 21 and the calculation time of the mixing unit 32, and then supplies the delayed audio signal to the mixing unit 42. The mixing unit 41 calculates a product of a value obtained by cubed the value of the audio signal at the same time by the mixing unit 32 and the value of the audio signal at the same time. For this reason, a value obtained by raising the value of the audio signal at the same time to the fourth power is output from the mixing unit 42. Thus, the output signal of the mixing unit 42 includes a frequency component that is four times the frequency component of the audio signal. 2 is attenuated by the HPF 43, and the component of the fourth harmonic band shown in FIG. 2 passes through the HPF 43. The signal that has passed through the HPF 43 is supplied to the adder 11 after being delayed by the delay unit 44 for a predetermined time.

  In addition, in the high frequency generation unit 5, the delay unit 51 delays the audio signal at that time by the calculation time of the mixing unit 21, the calculation time of the mixing unit 32, and the calculation time of the mixing unit 42, and then causes the mixing unit 52 to Supply. The mixing unit 52 calculates a product of a value obtained by raising the value of the audio signal at the same time by the fourth power by the mixing unit 42 and the value of the audio signal at the same time. Therefore, a value obtained by raising the value of the audio signal at the same time to the fifth power is output from the mixing unit 52. Thus, the output signal of the mixing unit 52 includes a frequency component that is five times the frequency component of the audio signal. 2 is attenuated by the HPF 53, and the component of the fifth harmonic band shown in FIG. 2 passes through the HPF 53. The signal that has passed through the HPF 53 is supplied to the adder 11.

  In this way, the input audio signal and the signal of the second to fifth harmonic components generated from the audio signal at the same time are supplied to the adder 11 at the same timing.

  The adder 11 calculates the sum of these signals and supplies the calculation result to the LPF 12. Then, a signal that has passed through the LPF 12 is output.

  As described above, according to the first embodiment, the high frequency generation units 2 to 5 serving as overtone generation means raise the audio signal to the 2nd to Nth power (N is an integer of 2 or more), and a signal in the second overtone band. (N-1) signals from the Nth harmonic band signal to the Nth harmonic band signal, and the adding unit 11 as an adding means inputs the (N-1) signals generated by the high frequency generating units 2 to 5 as input audio. Add to signal.

  As a result, a harmonic component is generated for each frequency component of the original audio signal, so that the harmonic component can be accurately generated from the original audio signal and an audio signal faithful to the original sound can be generated.

  Further, according to the first embodiment, the mixing unit 21 serving as the first multiplication unit squares the input audio signal, and the HPF 22 serving as the first high-pass filter is the signal generated by the mixing unit 21. The band component below the upper limit frequency of the audio signal is attenuated, and the adder 11 adds the signal after passing through the HPF 22 to the audio signal.

  Thereby, since the second harmonic component is generated for each frequency component of the original audio signal, the harmonic component can be accurately generated from the original audio signal, and an audio signal faithful to the original sound can be generated.

  Further, according to the first embodiment, the mixing unit 32 as the second multiplying unit multiplies the signal generated by the mixing unit 21 by the input audio signal, and the HPF 33 as the second high-pass filter is the mixing unit. Among the signals generated by 32, the frequency component equal to or less than twice the upper limit frequency of the audio signal is attenuated. Further, the mixing unit 42 as the third multiplying unit multiplies the signal generated by the mixing unit 32 by the input audio signal, and the HPF 43 as the third high-pass filter is an audio signal among the signals generated by the mixing unit 42. A frequency component equal to or lower than three times the upper limit frequency of the signal is attenuated. Also, the mixing unit 52 as the fourth multiplication means multiplies the signal generated by the mixing unit 42 by the input audio signal, and the HPF 53 as the fourth high-pass filter is the audio among the signals generated by the mixing unit 52. A frequency component equal to or less than four times the upper limit frequency of the signal is attenuated. Then, the adding unit 11 adds the signal after passing through the HPF 22, the signal after passing through the HPF 33, the signal after passing through the HPF 43, and the signal after passing through the HPF 53 to the audio signal.

  As a result, not only the second harmonic component but also multiple harmonic components are generated for each frequency component of the original audio signal, so the harmonic component is generated more accurately from the original audio signal and an audio signal faithful to the original sound is generated. can do.

Embodiment 2. FIG.
The audio signal processing device according to Embodiment 2 of the present invention is an audio signal processing device according to Embodiment 1 in which an HPF is provided before the high frequency generation units 2 to 5.

  FIG. 3 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 2 of the present invention. In FIG. 3, an HPF 61 is a high-pass filter having a filter frequency in the audible band. In the second embodiment, the filter frequency is half the upper limit frequency fH of the audible band. However, this filter frequency may be a frequency less than half of the upper limit frequency fH of the audible band. Note that the filter frequency of the HPF 61 may be any frequency within the frequency band of the input audio signal (for example, any frequency that is half or less than the upper limit frequency fHa of the input audio signal).

  The other components in FIG. 3 are the same as those in the first embodiment (FIG. 1), and the description thereof is omitted.

  Next, the operation of the above apparatus will be described.

  In the second embodiment, the frequency component signal that has passed through the HPF 61 in the input audio signal is supplied to the high frequency generators 2 to 5. The HPF 61 attenuates low frequency components not related to the generation of the second harmonic component to the fifth harmonic component.

  Note that the operation of the other components in FIG. 3 is the same as that in the first embodiment, and thus the description thereof is omitted.

  As described above, according to the second embodiment, the high frequency generators 2 to 5 raise the signal that has passed through the HPF 61 as the previous high-pass filter to the power of 2 to N (N = 5), and the signal in the second harmonic band (N-1) signals from N to N overtone band signals are generated, and the adder 11 adds (N-1) signals generated by the high frequency generators 2 to 5 to the audio signal. In particular, the HPF 61 has a filter frequency lower than a half of the upper limit frequency fHa of the input audio signal.

  As a result, frequency components that are not used for generating overtone components in the audio signal can be attenuated, and the amount of filter processing in the HPFs 22, 33, 43, and 53 in the high-frequency generation units 2 to 5 can be reduced. Therefore, when this audio signal processing apparatus is realized by a microcomputer or the like, the load on a processing unit such as a CPU can be reduced.

Embodiment 3 FIG.
The audio signal processing device according to Embodiment 3 of the present invention is an audio signal processing device according to Embodiment 2, in which an amplification unit that amplifies harmonic components of each order is provided in each of the high frequency generation units 2 to 5. is there.

  FIG. 4 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 3 of the present invention. In FIG. 4, the amplification unit 71 amplifies the signal that has passed through the HPF 22 in the high frequency generation unit 2. The amplification unit 72 amplifies the signal that has passed through the HPF 33 in the high frequency generation unit 3. The amplification unit 73 amplifies the signal that has passed through the HPF 43 in the high frequency generation unit 4. The amplification unit 74 amplifies the signal that has passed through the HPF 53 in the high frequency generation unit 5.

  The other components in FIG. 4 are the same as those in Embodiment 2 (FIG. 3), and the description thereof is omitted.

  Next, the operation of the above apparatus will be described.

  In the third embodiment, in the high frequency generators 2, 3, 4 and 5, the signals of the second to fifth harmonic components that have passed through the HPFs 22, 33, 43 and 53 are amplified by the amplifiers 71, 72, 73 and 74, respectively. The The signals amplified by the amplification units 71, 72, 73, 74 are supplied to the addition unit 11 as they are or after being delayed by the delay units 23, 24, 44.

  The operation of the other components in FIG. 4 is the same as that in the second embodiment, and a description thereof will be omitted.

  As described above, according to the third embodiment, in the high frequency generation units 2 to 5, the amplification units 71, 72, 73, and 74 serving as amplification units respectively receive the second harmonic band signal to the fifth harmonic band signal. Amplify.

  Thereby, the level of the harmonic component of each order among the harmonic components can be freely set, and an audio signal faithful to the original sound can be generated.

Embodiment 4 FIG.
The audio signal processing device according to Embodiment 4 of the present invention is the same as the audio signal processing device according to Embodiment 3, except that each high frequency generation unit is replaced with one HPF 61 provided before the high frequency generation units 2 to 5. 2 to 5 are provided with HPF separately.

  FIG. 5 is a block diagram showing a configuration of an audio signal processing apparatus according to Embodiment 4 of the present invention. In FIG. 5, the HPF 81 attenuates a frequency component equal to or lower than a predetermined filter frequency corresponding to the second harmonic component in the input audio signal in the high frequency generation unit 2. The HPF 82 attenuates a frequency component equal to or lower than a predetermined filter frequency corresponding to the third harmonic component in the input audio signal in the high frequency generator 3. The HPF 83 attenuates the frequency component equal to or lower than a predetermined filter frequency corresponding to the fourth harmonic component in the input audio signal in the high frequency generation unit 4. The HPF 84 attenuates a frequency component equal to or lower than a predetermined filter frequency corresponding to the fifth harmonic component in the input audio signal in the high frequency generation unit 5.

  The other components in FIG. 5 are the same as those in Embodiment 3 (FIG. 4), and the description thereof is omitted.

  Next, the operation of the above apparatus will be described.

  In the fourth embodiment, in the high frequency generator 2, a second harmonic component signal is generated by the mixing unit 21, HPF 22, and the like based on the frequency component signal that has passed through the HPF 81 in the input audio signal. The HPF 81 attenuates low frequency components not related to the generation of the second harmonic component. In the fourth embodiment, the filter frequency of the HPF 81 is a frequency that is half or less than the upper limit frequency fH of the audible band. By setting in this way, unnecessary frequency components are cut in advance, and the output signal of the mixing unit 21 includes frequency components from the upper limit frequency fH of the audible band to twice that frequency. When the frequency band of the input audio signal does not match the audible band, the filter frequency of the HPF 81 may be a frequency that is half or less than the upper limit frequency fHa of the input audio signal.

  In addition, in the high frequency generation unit 3, a third harmonic component signal is generated by the mixing unit 32, HPF 33, and the like based on the frequency component signal that has passed through the HPF 82 in the input audio signal. The HPF 82 attenuates low frequency components not related to the generation of the third harmonic component. In the fourth embodiment, the filter frequency of the HPF 82 is a frequency that is two-thirds or less of the upper limit frequency fH of the audible band. By setting in this way, unnecessary frequency components are cut in advance, and the output signal of the mixing unit 32 includes frequency components of 2 to 3 times the upper limit frequency fH of the audible band. If the frequency band of the input audio signal does not match the audible band, the filter frequency of the HPF 82 may be a frequency that is two-thirds or less of the upper limit frequency fHa of the input audio signal.

  Further, in the high frequency generation unit 4, a quadrature component signal is generated by the mixing unit 42, the HPF 43, and the like based on the frequency component signal that has passed through the HPF 83 in the input audio signal. The HPF 83 attenuates low frequency components not related to the generation of the fourth harmonic component. In the fourth embodiment, the filter frequency of the HPF 83 is set to a frequency that is three quarters or less than the upper limit frequency fH of the audible band. By setting in this way, unnecessary frequency components are cut, and the output signal of the mixing unit 42 includes frequency components from 3 to 4 times the upper limit frequency fH of the audible band. If the frequency band of the input audio signal does not match the audible band, the filter frequency of the HPF 83 may be a frequency that is three quarters or less than the upper limit frequency fHa of the input audio signal.

  Further, in the high frequency generation unit 5, a signal of a fifth harmonic component is generated by the mixing unit 52, HPF 53, and the like based on the frequency component signal that has passed through the HPF 84 in the input audio signal. The HPF 84 attenuates low frequency components not related to the generation of the fifth harmonic component. In the fourth embodiment, the filter frequency of the HPF 84 is set to a frequency that is 4/5 or less than the upper limit frequency fH of the audible band. By setting in this way, unnecessary frequency components are cut, and the output signal of the mixing unit 52 includes frequency components of 4 to 5 times the upper limit frequency fH of the audible band. If the frequency band of the input audio signal does not match the audible band, the filter frequency of the HPF 84 may be a frequency that is 4/5 or less than the upper limit frequency fHa of the input audio signal.

  Note that the operation of the other components in FIG. 5 is the same as that in the first embodiment, and thus the description thereof is omitted.

  As described above, according to the fourth embodiment, in the high-frequency generators 2 to 5, the HPFs 81 to 84 as the front-stage high-pass filters are one or more of signals from the second harmonic band signal to the N harmonic band signal. For each of these signals, there is a filter frequency in the frequency band of the audio signal before the 2nd-Nth power calculation of the audio signal. The HPFs 81 to 84 have filter frequencies corresponding to the corresponding overtone bands, that is, the orders of overtones.

  As a result, for each harmonic order, the frequency components that are not used to generate the harmonic component in the audio signal are attenuated, and the amount of calculation of the filter processing in the HPFs 22, 33, 43, and 53 in the high frequency generators 2 to 5 is reduced. Can be reduced. Therefore, when this audio signal processing apparatus is realized by a microcomputer or the like, the load on a processing unit such as a CPU can be reduced.

  Each embodiment described above is a preferred example of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. It is.

  For example, in the third embodiment, the high frequency generation units 2, 3, 4, and 5 are provided with the amplification units 71, 72, 73, and 74. However, the high frequency generation units 2 and 4 that correspond to even-order high-frequency components are provided. Only the amplifying units 71 and 73 may be provided, or the amplifying units 72 and 74 may be provided only in the high-frequency generating units 3 and 5 corresponding to odd-order high-frequency components. Further, the amplification factors of the amplification units 71, 72, 73, and 74 may be variable.

  In each of the above embodiments, the audible band is from 20 Hz to 20 kHz, but the range of the frequency component included in the original audio signal may be set as the audible band.

  In each of the above embodiments, the LPF 12 at the final stage and the delay units 23, 31, 34, 41, 44, and 51 are theoretically necessary, but their effects cannot be perceived by human audibility or almost. If they cannot be detected, they may be omitted. When these elements are realized by a processing unit and a program, it is possible to reduce the load on the processor by omitting these elements. When these elements are realized by elements, these elements By omitting, the circuit scale and cost can be reduced.

  When the HPF 61 is provided as a pre-stage high pass filter as in the second and third embodiments, the HPF 22 of the high frequency generator 2 may be omitted with the filter frequency of the HPF 61 as a predetermined frequency. In this case, the output signal of the mixing unit 21 is supplied to the adding unit 11 without passing through the post-delay filter by the delay unit 23.

  The present invention is applicable to, for example, a digital audio player and a communication device.

FIG. 1 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating a correspondence relationship between the frequency band of the second to fifth harmonic components generated in the first embodiment and the frequency band of the original audio signal. FIG. 3 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 2 of the present invention. FIG. 4 is a block diagram showing the configuration of the audio signal processing apparatus according to Embodiment 3 of the present invention. FIG. 5 is a block diagram showing a configuration of an audio signal processing apparatus according to Embodiment 4 of the present invention. FIG. 6 is a block diagram showing an example of a conventional audio signal processing apparatus.

Explanation of symbols

2, 3, 4, 5 High frequency generator (overtone generator)
11 Adder (addition means)
21 Mixing unit (first multiplication means)
22 HPF (first high-pass filter)
32 mixing section (second multiplication means)
33 HPF (second high-pass filter)
42 Mixing unit (third multiplication means)
43 HPF (third high-pass filter)
52 mixing section (fourth multiplication means)
53 HPF (fourth high-pass filter)
61 HPF (previous high-pass filter)
71, 72, 73, 74 Amplifying section (amplifying means)
81, 82, 83, 84 HPF (previous high-pass filter)

Claims (10)

First multiplication means for squaring the audio signal;
A first high-pass filter for attenuating a band component below the upper limit frequency of the audio signal among the signals generated by the first multiplication means;
Adding means for adding the signal after passing through the first high-pass filter to the audio signal;
An audio signal processing apparatus comprising: Second multiplying means for multiplying the signal generated by the first multiplying means by the audio signal;
A second high-pass filter for attenuating a frequency component less than twice the upper limit frequency of the audio signal among the signals generated by the second multiplication means,
The adding means adds the signal after passing through the first high-pass filter and the signal after passing through the second high-pass filter to the audio signal;
The audio signal processing apparatus according to claim 1. Third multiplication means for multiplying the audio signal by the signal generated by the second multiplication means;
A third high-pass filter for attenuating a frequency component equal to or lower than three times the upper limit frequency of the audio signal among the signals generated by the third multiplication means;
The adding means adds the signal after passing through the first high-pass filter, the signal after passing through the second high-pass filter, and the signal after passing through the third high-pass filter to the audio signal. To do,
The audio signal processing apparatus according to claim 2. Fourth multiplying means for multiplying the audio signal by the signal generated by the third multiplying means;
A fourth high-pass filter for attenuating a frequency component equal to or lower than four times the upper limit frequency of the audio signal among the signals generated by the fourth multiplication means,
The adding means includes a signal after passing through the first high-pass filter, a signal after passing through the second high-pass filter, a signal after passing through the third high-pass filter, and the fourth high-pass filter. Adding the signal after passing through to the audio signal,
The audio signal processing apparatus according to claim 3. Harmonic generation means for generating an (N-1) number of signals from the second harmonic band signal to the N harmonic band signal by raising the audio signal to the power of 2 to N (N is an integer of 2 or more);
Adding means for adding (N-1) signals generated by the harmonic overtone generating means to the audio signal;
An audio signal processing apparatus comprising: A pre-stage high-pass filter having a filter frequency within the frequency band of the audio signal;
The harmonic generation means generates (N-1) signals from the second harmonic band signal to the N harmonic band signal by raising the signal that has passed through the preceding high-pass filter to the 2nd to Nth power,
The adding means adds (N−1) signals generated by the harmonic sound generating means to the audio signal;
The audio signal processing apparatus according to claim 5.   The audio signal processing apparatus according to claim 6, wherein the front-stage high-pass filter has a filter frequency that is equal to or lower than a half of an upper limit frequency of the audio signal.   The harmonic overtone generating means includes a second harmonic band signal to an Nth harmonic band signal for each of one or more signals within the frequency band of the audio signal before the calculation of the 2nd to 2nd powers of the audio signal. 6. The audio signal processing apparatus according to claim 5, further comprising one or a plurality of preceding high-pass filters having a filter frequency.   9. The audio signal processing apparatus according to claim 8, wherein the front-stage high-pass filter has a filter frequency corresponding to a corresponding overtone band.   6. The audio signal processing apparatus according to claim 5, wherein the overtone generating means includes one or a plurality of amplifying means for amplifying one or a plurality of signals in a signal from a second harmonic band to a signal of the N harmonic band, respectively. .

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