Audio signal processing unit

Abstract

We provide an "audio signal processing device" that achieves good localization while maintaining sound quality. [Solution] The system includes: a harmonic signal generation unit that generates a harmonic signal AS including a signal obtained by multiplying the frequency of the audio signal S to be processed by k (where k is an integer of 2 or more); a left audio signal generation unit that generates a left audio signal by convolving the audio signal S with a head transfer function from the target localization position of the audio signal S to the listener's left ear; a right audio signal generation unit that generates a right audio signal by convolving the audio signal S with a head transfer function from the target localization position to the listener's right ear; a left combining unit that generates a left channel audio signal L by combining the left audio signal and the harmonic signal; and a right combining unit that generates a right channel audio signal R by combining the right audio signal and the harmonic signal.

Description

Technical Field

[0001] The present invention relates to an audio signal processing apparatus.

Background Art

[0002] There is known an audio signal processing apparatus that provides a sense of sound localization to a sound localization target position by convolution of an acoustic transfer characteristic (head transfer function) from the sound localization target position to each of the left and right ears of a listener with an audio signal (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since a human's ability to perceive the direction of a sound with a narrow frequency band is low, sufficient sense of localization may not be provided even if the head transfer function is convolved with an audio signal having a narrow sound band as described above and output. In addition, when the head transfer function is convolved with an audio signal and output, the sound quality of the output sound may become different from that of the original audio signal. Therefore, an object of the present invention is to realize a good sense of localization while maintaining the sound quality of an audio signal.

Means for Solving the Problems

[0005] In order to achieve the above object, the present invention includes a harmonic signal generation unit that generates a harmonic signal including a signal obtained by multiplying the frequency of a target audio signal, which is an audio signal to be processed, by k times (where k is an integer of 2 or more), The present invention provides an audio signal processing device comprising: a left audio signal generation unit that generates a left audio signal by convolving the target audio signal with a head-related transfer function from the target localization position of the audio signal to the listener's left ear; a right audio signal generation unit that generates a right audio signal by convolving the target audio signal with a head-related transfer function from the target localization position to the listener's right ear; a left synthesis unit that generates a left channel audio signal by combining the left audio signal and the harmonic signal; and a right synthesis unit that generates a right channel audio signal by combining the right audio signal and the harmonic signal.

[0006] Furthermore, in order to achieve the above objectives, the present invention includes: a harmonic signal generation unit that generates a harmonic signal including a signal obtained by multiplying the frequency of a target audio signal, which is an audio signal to be processed, by k (where k is an integer of 2 or more); a left harmonic signal generation unit that generates a left harmonic signal by adjusting the gain of the harmonic signal so that the level of the harmonic signal increases as the direction is to the left, according to the direction of the target localization position of the audio signal; a right harmonic signal generation unit that generates a right harmonic signal by adjusting the gain of the harmonic signal so that the level of the harmonic signal increases as the direction is to the right, according to the direction of the target localization position of the audio signal; and a left audio signal generation unit that generates a left audio signal by convolving the target audio signal with the head transfer function from the target localization position to the listener's left ear. The present invention provides an audio signal processing device comprising: a right audio signal generation unit that generates a right audio signal by convolving the head transfer function from the target localization position to the listener's right ear onto the target audio signal; a left synthesis unit that generates a left channel audio signal by combining the left audio signal and the left harmonic signal; and a right synthesis unit that generates a right channel audio signal by combining the right audio signal and the right harmonic signal.

[0007] Furthermore, in order to achieve the above objectives, the present invention provides an audio signal processing device comprising: a harmonic signal generation unit that generates a harmonic signal including a signal obtained by multiplying the frequency of a target audio signal, which is an audio signal to be processed, by k (where k is an integer of 2 or more); a harmonic added signal synthesis unit that generates a harmonic added signal by combining the target audio signal and the harmonic signal; a left channel audio signal generation unit that generates a left channel audio signal by convolving the harmonic added signal with a head transfer function from the target localization position of the audio signal to the listener's left ear; and a right channel audio signal generation unit that generates a right channel audio signal by convolving the harmonic added signal with a head transfer function from the target localization position to the listener's right ear.

[0008] Here, the harmonic signal generation unit described above may generate signals by multiplying the frequency of the target audio signal by i, using each integer i from 2 to n (where n≧k and n>2), and then synthesizing the generated signals to produce the harmonic signal. Furthermore, in order to achieve the above objectives, the present invention provides an audio signal processing device comprising: a left harmonic signal generation unit that generates a left harmonic signal including a signal obtained by multiplying the frequency of a target left channel signal, which is the signal of the left channel of an audio signal consisting of left and right channels to be processed, by k (where k is an integer of 2 or more); a right harmonic signal generation unit that generates a right harmonic signal including a signal obtained by multiplying the frequency of a target right channel signal, which is the signal of the right channel of the audio signal, by L (where L is an integer of 2 or more); a left audio signal generation unit that generates a left audio signal by convolving the target left channel signal with a head transfer function from the target localization position of the audio signal to the listener's left ear; a right audio signal generation unit that generates a right audio signal by convolving the target right channel signal with a head transfer function from the target localization position to the listener's right ear; a left combining unit that generates a left channel audio signal by combining the left audio signal and the left harmonic signal; and a right combining unit that generates a right channel audio signal by combining the right audio signal and the right harmonic signal.

[0009] Furthermore, in order to achieve the above objectives, the present invention provides an audio signal processing device comprising: a left harmonic signal generation unit that generates a harmonic signal including a signal obtained by multiplying the frequency of a target left channel signal, which is the left channel signal of an audio signal consisting of left and right channels to be processed, by k (where k is an integer of 2 or more); a right harmonic signal generation unit that generates a harmonic signal including a signal obtained by multiplying the frequency of a target right channel signal, which is the right channel signal of the audio signal, by L (where L is an integer of 2 or more); a left harmonic added signal synthesis unit that generates a left harmonic added signal by combining the target left channel signal and the left harmonic signal; a right harmonic added signal synthesis unit that generates a right harmonic added signal by combining the target right channel signal and the right harmonic signal; a left channel audio signal generation unit that generates a left channel audio signal by convolving the left harmonic added signal with a head transfer function from the target localization position of the audio signal to the listener's left ear; and a right channel audio signal generation unit that generates a right channel audio signal by convolving the right harmonic added signal with a head transfer function from the target localization position to the listener's right ear.

[0010] Here, the left harmonic signal generation unit may generate a signal for each integer i from 2 to n (where n≧k and n>2) by multiplying the frequency of the target left channel signal by i, and synthesize the generated signals to generate the left harmonic signal. The right harmonic signal generation unit may generate a signal for each integer i from 2 to m (where m≧L and m>2) by multiplying the frequency of the target right channel signal by i, and synthesize the generated signals to generate the right harmonic signal.

[0011] According to the audio signal processing device described above, an audio signal is generated by combining a signal obtained by convolving a head-related transfer function into the target audio signal, which is the audio signal to be processed, with a harmonic signal whose frequency is an integer multiple of the audio signal to be processed, or a signal obtained by convolving a head-related transfer function into a harmonic signal.

[0012] Therefore, by convolving the target audio signal with a head-related transfer function into the generated audio signal, a good sense of localization can be provided, while the harmonic signals included in the generated audio signal can suppress the tonal quality from becoming inconsistent with that of the target audio signal. [Effects of the Invention]

[0013] As described above, according to the present invention, it is possible to achieve good localization while maintaining the sonic quality of the audio signal. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows the configuration of an audio signal processing device according to an embodiment of the present invention. [Figure 2] This figure shows another example configuration of an audio signal processing apparatus according to an embodiment of the present invention. [Figure 3] This figure shows the configuration of the harmonic addition section according to an embodiment of the present invention. [Figure 4] This figure shows another example configuration of an audio signal processing apparatus according to an embodiment of the present invention. [Figure 5] This figure shows another example configuration of an audio signal processing apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below. Figure 1 shows the configuration of the audio signal processing device 1 according to this embodiment. As shown in the diagram, the audio signal processing device 1 processes the one-channel audio signal S output by the sound source device 2 to obtain a sense of localization, generating two-channel audio signals, an L (left) channel and an R (right) channel, and outputs them to the left speaker 3 and the right speaker 4.

[0016] The audio signal processing device 1 includes a harmonic generation unit 11, a head-related transfer function convolution unit 12, a localization control unit 13, a harmonic amplifier 14, an L-channel signal amplifier 15, an R-channel signal amplifier 16, an L-channel synthesizer 17, an R-channel synthesizer 18, an L-channel output amplifier 19, and an R-channel output amplifier 20.

[0017] Further, the head-related transfer function convolution unit 12 includes a left-ear head-related transfer function convolution unit 121 and a right-ear head-related transfer function convolution unit 122. The harmonic generation unit 11 generates signals (harmonic signals) of the i-th harmonic of the audio signal S output from the sound source device 2, where i is an integer from 1 to N (N ≥ 2), and synthesizes the generated signals and outputs them as a signal AS. However, the harmonic generation unit 11 may use i as one integer greater than or equal to 1, generate a signal (harmonic signal) of the i-th harmonic of the audio signal S output from the sound source device 2, and output it as a signal AS. The signal AS is level-adjusted with a predetermined gain by the harmonic amplifier 14 and sent to the L-channel synthesizer 17 and the R-channel synthesizer 18. The localization control unit 13 sets the head-related transfer function from the localization position to the listener's left ear in the left-ear head-related transfer function convolution unit 121 and the head-related transfer function from the localization position to the listener's right ear in the right-ear head-related transfer function convolution unit 122 according to the set target localization position of the sound image of the audio signal S.

[0018] Here, the localization position of the sound image of the target audio signal S may be obtained by setting the distance from the localization position to the listener as a predetermined distance according to the direction of the set localization position with respect to the listener. The left-ear head-related transfer function convolution unit 121 convolves the head-related transfer function set by the localization control unit 13 with the audio signal S output from the sound source device 2 and outputs it as an audio signal LHS, and the right-ear head-related transfer function convolution unit 122 convolves the head-related transfer function set by the localization control unit 13 with the audio signal S output from the sound source device 2 and outputs it as an audio signal RHS.

[0019] The audio signal LHS is adjusted to a predetermined gain level by the L-channel signal amplifier 15 and sent to the L-channel combiner 17, and the audio signal RHS is adjusted to a predetermined gain level by the R-channel signal amplifier 16 and sent to the R-channel combiner 18. The L-channel combiner 17 combines the signal AS input from the harmonic amplifier 14 and the audio signal LHS input from the L-channel signal amplifier 15, and outputs it to the left speaker 3 via the L-channel output amplifier 19. The R-channel combiner 18 combines the signal AS input from the harmonic amplifier 14 and the audio signal RHS input from the R-channel signal amplifier 16, and outputs it to the right speaker 4 via the R-channel output amplifier 20.

[0020] Furthermore, the gains of the harmonic amplifier 14, the L-channel signal amplifier 15, and the R-channel signal amplifier 16 may be adjusted arbitrarily by the user to obtain a predetermined sense of position and sound quality that the user finds appropriate. With this configuration of the audio signal processing device 1, a good sense of localization is provided by the signal obtained by convolving the head-related transfer function into the audio signal S output by the sound source device 2, which is included in the output of the audio signal processing device 1. At the same time, the harmonic signals generated by the harmonic generation unit 11, which are included in the output of the audio signal processing device 1, can suppress the output of the audio signal processing device 1 from becoming different from the audio signal S.

[0021] Here, the audio signal processing device 1 may be configured as shown in Figure 2. As shown in the diagram, this audio signal processing device 1 is an improved version of the configuration shown in Figure 1, with the addition of an L-channel harmonic adjustment amplifier 101 and an R-channel harmonic adjustment amplifier 102. The L-channel harmonic adjustment amplifier 101 adjusts the level of the signal AS input from the harmonic amplifier 14 with a gain GL set by the positioning control unit 13 and outputs it to the L-channel combiner 17. The R-channel harmonic adjustment amplifier 102 adjusts the level of the signal AS input from the harmonic amplifier 14 with a gain GR set by the positioning control unit 13 and outputs it to the R-channel combiner 18.

[0022] Furthermore, the L-channel combiner 17 combines the signal AS input from the L-channel harmonic adjustment amplifier 101 and the audio signal LHS input from the L-channel signal amplifier 15, and outputs it to the left speaker 3 via the L-channel output amplifier 19. The R-channel combiner 18 combines the signal AS input from the R-channel harmonic adjustment amplifier 102 and the audio signal RHS input from the R-channel signal amplifier 16, and outputs it to the right speaker 4 via the R-channel output amplifier 20.

[0023] The positioning control unit 13 controls the gain GL of the L-channel harmonic adjustment amplifier 101 and the gain GR of the R-channel harmonic adjustment amplifier 102 according to the direction of the localization position of the sound image of the target audio signal S relative to the listener. The more the direction is to the left, the larger the gain GL and the smaller the gain GR, and the more the direction is to the right, the larger the gain GR and the smaller the gain GL.

[0024] With this configuration of the audio signal processing device 1, the sense of sound localization represented by the audio signal S output by the audio signal processing device 1 can be further enhanced. By the way, the harmonic generation unit 11 of the audio signal processing device 1 shown in Figures 1 and 2 above may be replaced with the harmonic addition unit 111 shown in Figure 3. As shown in the figure, the harmonic addition unit 111 includes the harmonic generation unit 11 described above, the fundamental tone level adjustment amplifier 1111, and the harmonic fundamental tone synthesis unit 1112. The fundamental tone level adjustment amplifier 1111 adjusts the level of the audio signal S output by the sound source device 2 with a preset gain and outputs it to the harmonic fundamental tone synthesis unit 1112. The harmonic fundamental tone synthesis unit 1112 combines the output of the harmonic generation unit 11 with the output of the fundamental tone level adjustment amplifier 1111 and outputs it as signal AS.

[0025] Here, when the gain of the fundamental level adjustment amplifier 1111 is set to block the audio signal S, the signal AS at the output of the harmonic addition unit 111 becomes equal to the output of the harmonic generation unit 11. Also, when the gain of the fundamental level adjustment amplifier 1111 is set to allow the audio signal S to pass through as is, the signal AS at the output of the harmonic addition unit 111 contains the components of the audio signal S as they are.

[0026] The value of the fundamental frequency level adjustment amplifier gain is set to a value that has been pre-tuned to obtain the desired relationship between localization and sound quality. Furthermore, the configuration of the audio signal processing device 1 can be changed from the configurations shown in Figures 1 and 2 to the configuration shown in Figure 4. In the configuration shown in Figure 4, the audio signal processing device 1 includes the harmonic addition unit 111 shown in Figure 3, the head-transfer function convolution unit 12, the localization control unit 13, the L channel output amplifier 19, and the R channel output amplifier 20. Then, the harmonic addition unit 111 receives the audio signal S output by the sound source device 2, and the output AS of the harmonic addition unit 111 becomes the input to both the left earcephalic transfer function convolution unit 121 and the right earcephalic transfer function convolution unit 122 of the head-to-head transfer function convolution unit 12. Furthermore, the output of the left orbital transfer function convolution section 121 is output to the left speaker 3 via the L channel output amplifier 19, and the output of the right orbital transfer function convolution section 122 is output to the right speaker 4 via the R channel output amplifier 20. In the configuration shown in Figure 4, the fundamental level adjustment amplifier 1111 of the harmonic addition unit 111 may be omitted, so that the component of the audio signal S is directly included in the output signal AS of the harmonic addition unit 111. With this configuration of the audio signal processing device 1, a good sense of localization is provided by the signal obtained by convolving the head-level transfer function into the audio signal S output by the sound source device 2, which is included in the output of the audio signal processing device 1. At the same time, the signal obtained by convolving the head-level transfer function into the harmonic signals generated by the harmonic generation unit 11, which is included in the output of the audio signal processing device 1, can suppress to a certain extent the output of the audio signal processing device 1 from becoming different from the audio signal S.

[0027] This embodiment has been described above. Herein, we have described the case where the sound source device 2 outputs a single-channel audio signal S, but this embodiment can also be applied to the case where the sound source device 2 outputs a two-channel audio signal S. In other words, with respect to the audio signal processing device 1 shown in Figures 1 and 2, when the audio signal S output by the sound source device 2 is 2-channel, as shown in Figure 5, a left harmonic addition unit 1201 and a right harmonic addition unit 1202 are provided instead of the harmonic addition unit 111 in Figure 1. The left harmonic addition unit 1201 and the right harmonic addition unit 1202 have the same configuration and function as the harmonic addition unit 111 in Figure 1.

[0028] Furthermore, instead of the harmonic amplifier 14 in Figure 1, a left harmonic amplifier 1203 and a right harmonic amplifier 1204 are provided. Then, the audio signal LS of the L channel output by the audio signal processing device 1 is used as the input to the left harmonic addition unit 1201, and the audio signal RS of the R channel output by the audio signal processing device 1 is used as the input to the right harmonic addition unit 1202. Furthermore, the output of the left harmonic addition unit 1201 is output to the L channel synthesizer 17 via the left harmonic amplifier 1203, and the output of the right harmonic addition unit 1202 is output to the R channel synthesizer 18 via the right harmonic amplifier 1204. The L-channel combiner 17 combines the signal input from the left harmonic amplifier 1203 with the audio signal LHS input from the L-channel signal amplifier 15 and outputs it to the left speaker 3 via the L-channel output amplifier 19. The R-channel combiner 18 combines the signal AS input from the right harmonic amplifier 1204 with the audio signal RHS input from the R-channel signal amplifier 16 and outputs it to the right speaker 4 via the R-channel output amplifier 20.

[0029] Furthermore, in the audio signal processing device 1 shown in Figure 4, if the audio signal S output by the sound source device 2 is 2-channel, a left harmonic addition unit 1201 and a right harmonic addition unit 1202 are provided instead of the harmonic addition unit 111 in Figure 4. The audio signal LS of the L channel output by the audio signal processing device 1 is used as the input to the left harmonic addition unit 1201, and the audio signal RS of the R channel output by the audio signal processing device 1 is used as the input to the right harmonic addition unit 1202. In addition, the output of the left harmonic addition unit 1201 is used as the input to the left orbital-cephalic transfer function convolution unit 121, and the output of the right harmonic addition unit 1202 is used as the input to the right orbital-cephalic transfer function convolution unit 122.

[0030] Here, each audio signal processing device 1 is configured to output to the left speaker 3 and the right speaker 4, but the audio signal processing device 1 may also output to an audio recording device, and the audio recording device may record the audio signal output by the audio signal processing device 1.

[0031] Furthermore, each of the above audio signal processing devices 1 can be applied as part of a game console or an in-car audio system, for example, to convert game sound effects output as audio signals S from a sound source device 2, or warning sounds emitted to occupants in a car, into sound effects with a sense of localization. [Explanation of symbols]

[0032] 1...Audio signal processing unit, 2...Sound source unit, 3...Left speaker, 4...Right speaker, 11...Harmonic generation unit, 12...Head-mount transfer function convolution unit, 13...Localization control unit, 14...Harmonic amplifier, 15...L channel signal amplifier, 16...R channel signal amplifier, 17...L channel synthesizer, 18...R channel synthesizer, 19...L channel output amplifier, 20...R channel output amplifier, 101...L channel harmonic adjustment amplifier, 102...R channel harmonic adjustment amplifier, 111...Harmonic addition unit, 121...Left ear-head transfer function convolution unit, 122...Right ear-head transfer function convolution unit, 1111...Fundamental level adjustment amplifier, 1112...Harmonic fundamental synthesis unit, 1201...Left harmonic addition unit, 1202...Right harmonic addition unit, 1203...Left harmonic amplifier, 1204...Right harmonic amplifier.

Claims

1. A harmonic signal generation unit generates a harmonic signal that includes a signal obtained by multiplying the frequency of the target audio signal, which is the audio signal to be processed, by k (where k is an integer of 2 or more), A left audio signal generation unit generates a left audio signal by convolving the head-related transfer function from the target localization position of the audio signal to the listener's left ear onto the aforementioned target audio signal. A right audio signal generation unit generates a right audio signal by convolving the head transfer function from the target localization position to the listener's right ear onto the target audio signal, A left synthesizer unit combines the left audio signal and the harmonic signal to generate an audio signal for the left channel, An audio signal processing apparatus characterized by having a right combining unit that combines the right audio signal and the harmonic signal to generate an audio signal for the right channel.

2. A harmonic signal generation unit generates a harmonic signal that includes a signal obtained by multiplying the frequency of the target audio signal, which is the audio signal to be processed, by k (where k is an integer of 2 or more), A left harmonic signal generation unit generates a left harmonic signal by adjusting the gain of the aforementioned harmonic signal level so that it becomes larger as the direction is to the left, according to the direction of the target localization position of the audio signal. A right harmonic signal generation unit generates a right harmonic signal by adjusting the gain of the harmonic signal level according to the direction of the target localization position of the audio signal, such that the level increases as the direction is to the right; A left audio signal generation unit generates a left audio signal by convolving the head transfer function from the target localization position to the listener's left ear onto the target audio signal, A right audio signal generation unit generates a right audio signal by convolving the head transfer function from the target localization position to the listener's right ear onto the target audio signal, A left synthesizer unit combines the left audio signal and the left harmonic signal to generate a left channel audio signal, An audio signal processing apparatus characterized by having a right combining unit that combines the right audio signal and the right harmonic signal to generate an audio signal for the right channel.

3. A harmonic signal generation unit generates a harmonic signal that includes a signal obtained by multiplying the frequency of the target audio signal, which is the audio signal to be processed, by k (where k is an integer of 2 or more), A harmonic-added signal synthesis unit that synthesizes the target audio signal and the harmonic signal to generate a harmonic-added signal, A left channel audio signal generation unit generates a left channel audio signal by convolving the head-related transfer function from the target localization position of the audio signal to the listener's left ear into the aforementioned harmonic-added signal, An audio signal processing device characterized by having a right channel audio signal generation unit that convolves the harmonic-added signal with a head-related transfer function from the target localization position to the listener's right ear to generate a right channel audio signal.

4. An audio signal processing apparatus according to claim 1, 2, or 3, The harmonic signal generation unit is characterized by generating a signal obtained by multiplying the frequency of the target audio signal by i, with each i being an integer from 2 to n (where n ≥ k and n > 2), and then combining the generated signals to generate the harmonic signal.

5. A left harmonic signal generation unit generates a left harmonic signal that includes a signal obtained by multiplying the frequency of the target left channel signal, which is the left channel signal of an audio signal consisting of left and right channels to be processed, by k (where k is an integer of 2 or more), A right harmonic signal generation unit generates a right harmonic signal that includes a signal obtained by multiplying the frequency of the target right channel signal, which is the signal of the right channel of the aforementioned audio signal, by L (where L is an integer of 2 or more), A left audio signal generation unit generates a left audio signal by convolving the head-related transfer function from the target localization position of the audio signal to the listener's left ear onto the target left channel signal, A right audio signal generation unit generates a right audio signal by convolving the head-related transfer function from the target localization position to the listener's right ear onto the aforementioned target right channel signal, A left synthesizer unit combines the left audio signal and the left harmonic signal to generate a left channel audio signal, An audio signal processing apparatus characterized by having a right combining unit that combines the right audio signal and the right harmonic signal to generate an audio signal for the right channel.

6. A left harmonic signal generation unit generates a harmonic signal that includes a signal obtained by multiplying the frequency of the target left channel signal, which is the left channel signal of an audio signal consisting of left and right channels to be processed, by k (where k is an integer of 2 or more), A right harmonic signal generation unit generates a harmonic signal that includes a signal obtained by multiplying the frequency of the target right channel signal, which is the signal of the right channel of the aforementioned audio signal, by L (where L is an integer of 2 or more), A left harmonic addition signal synthesis unit that synthesizes the target left channel signal and the left harmonic signal to generate a left harmonic addition signal, A right harmonic addition signal synthesis unit combines the target right channel signal and the right harmonic signal to generate a right harmonic addition signal, A left channel audio signal generation unit generates a left channel audio signal by convolving the head-related transfer function from the target localization position of the audio signal to the listener's left ear into the aforementioned left harmonic-added signal, An audio signal processing device characterized by having a right channel audio signal generation unit that convolves the right harmonic added signal with a head transfer function from the target localization position to the listener's right ear to generate a right channel audio signal.

7. An audio signal processing device according to claim 5 or 6, The left harmonic signal generation unit generates signals by multiplying the frequency of the target left channel signal by i, using each integer i from 2 to n (where n ≥ k and n > 2), and then synthesizes the generated signals to generate the left harmonic signal. The audio signal processing device is characterized in that the right harmonic signal generation unit generates a signal obtained by multiplying the frequency of the target right channel signal by i, with each i being an integer from 2 to m (where m ≥ L and m > 2), and then synthesizes the generated signals to generate the right harmonic signal.

Images