JP7359146B2 - Impulse response generation device, method, and program - Google Patents

Description

The present technology relates to an impulse response generation device, method, and program, and particularly relates to an impulse response generation device, method, and program that can obtain desired phase characteristics.

For example, when reproducing audio such as music, a technique is known in which an effect such as an effect is applied to the reproduced music by performing filter processing on the audio signal.

As such a technique, for example, a technique has been proposed in which a plurality of filters are combined to change the amplitude characteristics of an audio signal so as to bring about a bass emphasis effect (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2002-171589

Incidentally, in recent years, an increasing number of users are playing and listening to music through headphones instead of speakers, and audio reproduction using headphones is becoming mainstream.

On the other hand, most commercial content is basically mastered using speakers. As a result, there have been complaints that even if content such as mastered music is played through headphones while being played back through speakers, it is not possible to hear the rich bass tones that can be heard when playing back through speakers. That is, when content is played back through headphones, the way the low frequencies are heard is different from when it is played back through speakers, and it may not be possible to achieve the sound quality that the creator originally wanted to convey.

The applicant investigated this and found that the way low frequencies are heard is greatly influenced by the phase characteristics. In other words, it has been found that part of the cause lies in the large difference between the low-frequency phase characteristics of the speaker and the low-frequency phase characteristics of the headphones.

However, with the above-mentioned techniques, although the amplitude characteristics of the audio signal can be adjusted, it is not possible to make the phase characteristics of the audio signal a desired characteristic.

The present technology has been developed in view of this situation, and is intended to make it possible to obtain desired phase characteristics.

An impulse response generation device according to an aspect of the present technology includes a zero-filling processing unit that performs zero-filling processing that adds zero data to predetermined impulse information, and a zero-filling processing unit that performs FFT on the impulse information to which the zero data is added. an IFFT processing unit that generates a target characteristic impulse response having a predetermined phase characteristic by performing IFFT based on the phase characteristic obtained by the FFT and the flat amplitude characteristic. Be prepared.

An impulse response generation method or program according to one aspect of the present technology performs zero padding processing to add 0 data to predetermined impulse information, performs FFT on the impulse information to which the 0 data has been added, and The method includes a step of generating a target characteristic impulse response having a predetermined phase characteristic by performing IFFT based on the phase characteristic obtained by FFT and the flat amplitude characteristic.

In one aspect of the present technology, zero padding processing is performed to add 0 data to predetermined impulse information, FFT is performed on the impulse information to which the 0 data has been added, and the result obtained by the FFT is By performing IFFT based on the phase characteristic and the flat amplitude characteristic, a target characteristic impulse response having a predetermined phase characteristic is generated.

According to one aspect of the present technology, desired phase characteristics can be obtained.

Note that the effects described here are not necessarily limited, and may be any of the effects described in this disclosure.

FIG. 3 is a diagram illustrating the relationship between frequency characteristics and impulse response. FIG. 3 is a diagram illustrating reconstruction of an impulse response. FIG. 3 is a diagram showing frequency characteristics of a reconstructed impulse response. FIG. 3 is a diagram illustrating reconstruction of an impulse response. FIG. 3 is a diagram showing frequency characteristics of a reconstructed impulse response. FIG. 3 is a diagram illustrating reconstruction of an impulse response. FIG. 3 is a diagram showing frequency characteristics of a reconstructed impulse response. FIG. 2 is a diagram showing a configuration example of an impulse response generation device. 3 is a flowchart illustrating impulse response generation processing. FIG. 2 is a diagram showing a configuration example of an impulse response generation device. 3 is a flowchart illustrating impulse response generation processing. FIG. 2 is a diagram illustrating mastering of content. It is a diagram showing an example of the configuration of a playback device. It is a flowchart explaining playback processing. It is a diagram showing an example of the configuration of a playback device. It is a flowchart explaining playback processing. It is a diagram showing an example of the configuration of a playback device. It is a flowchart explaining playback processing. It is a diagram showing an example of the configuration of a playback device. It is a diagram showing an example of the configuration of a computer.

Embodiments to which the present technology is applied will be described below with reference to the drawings.

<First embodiment>
<About this technology>
This technology makes it possible to adjust only the phase characteristics of an audio signal without changing the amplitude characteristics (gain characteristics).

In other words, this technology generates an impulse response with a flat or nearly flat amplitude characteristic and a desired phase characteristic, thereby adjusting only the phase characteristic while maintaining the amplitude characteristic of the audio signal, and achieving the desired phase characteristic. It allows you to obtain.

In this technology, by performing FFT (Fast Fourier Transform) and IFFT (Inverse Fast Fourier Transform) on an impulse response that has the target phase characteristics, the amplitude characteristics are flat or nearly flat and desired. An impulse response with phase characteristics can be obtained. Here, the amplitude characteristic being flat or substantially flat means that, for example, the amplitude (gain) value at each frequency of the amplitude characteristic is 1 or approximately 1.

Specifically, in the present technology, a target impulse response is generated by the following method A1 or method A2.

That is, in method A1, first, 0 data (zero data) of an appropriate length is inserted before the impulse response whose phase is to be simulated, and FFT (fast Fourier transform) is performed.

An amplitude characteristic and a phase characteristic are obtained by such an FFT, but in order to make this amplitude characteristic flat, the amplitude (gain) value at each frequency of the amplitude characteristic is set to 1, and the flat amplitude characteristic and the FFT IFFT (inverse fast Fourier transform) is performed based on the phase characteristics obtained in . Then, the latter stage of the impulse response obtained by IFFT is fade-processed with an appropriate time constant to obtain the desired impulse response.

The impulse response obtained in this manner functions as an IIR (Infinite Impulse Response) filter that changes only the phase characteristic while maintaining the amplitude characteristic. Therefore, by convolving such an impulse response with an audio signal, only the phase characteristics can be adjusted.

Further, in method A2, FFT is performed on the impulse response whose phase is to be simulated without inserting 0 data, and FFT is performed with 0 data inserted on the simple impulse.

Then, the phase characteristics obtained by FFT for the impulse response and the phase characteristics obtained by FFT for the simple impulse with 0 data inserted are added, and the resulting phase characteristics and the amplitude value at each frequency are added. IFFT is performed based on a flat amplitude characteristic in which . Furthermore, the latter stage of the impulse response obtained by IFFT is faded with an appropriate time constant to obtain the desired impulse response.

In method A2, an impulse response with similar characteristics to that in method A1 can be obtained. In other words, it is possible to obtain an IIR filter that changes only the phase characteristics while maintaining the amplitude characteristics.

In addition, in method A2, if the phase characteristics obtained by FFT for the impulse response and the phase characteristics obtained by FFT for the simple impulse with 0 data inserted are subtracted rather than added, the original impulse response can be obtained. Impulse responses with characteristics opposite to the phase characteristics can be obtained.

By using the impulse responses obtained by the above methods A1 and A2, it is possible to reproduce sounds of the same quality even when different reproduction devices are used.

As a specific example, assume that there is content that has been mastered while playing back sound through speakers, and the content is played back through headphones.

In such a case, by convolving the audio signal of the content with an impulse response that has the opposite characteristics to the phase characteristics of the headphones, and also with an impulse response that has the same phase characteristics as the speakers, the phase characteristics of the headphones can be canceled and the speaker The phase characteristics of can be simulated. That is, even when playing back content with headphones, it is possible to play back the same quality of sound as when mastering.

Now, the present technology will be explained in more detail below.

For example, consider a case where there is content that has been mastered while the sound is played back through speakers, and the content is played back through headphones.

In this case, if it is possible to add only the low-frequency phase characteristics of the speakers used for mastering to the sound source of the content, that is, the audio signal of the content when played back with headphones, it would be possible to add only the low-frequency phase characteristics of the speakers used for mastering. It is assumed that you will be able to experience almost the same sound as the sound you are experiencing.

Generally, it is difficult to identify the speakers used in a mastering studio from arbitrary content. Furthermore, in the future, it may be possible to identify the speakers used in the mastering studio from content metadata, etc., but it is currently difficult to do so.

Therefore, since the characteristics of an IIR type HPF (High Pass Filter) with a cutoff frequency Fc = 50 Hz are close to the characteristics of a speaker, the characteristics of such an HPF will be considered as pseudo speaker characteristics.

For example, the relationship between the frequency characteristics, that is, the amplitude characteristics (gain characteristics) and phase characteristics of an IIR type HPF with a cutoff frequency Fc of 50 Hz, and the impulse response of the HPF is shown in FIG.

In FIG. 1, a portion indicated by an arrow Q11 indicates an amplitude characteristic of the frequency characteristics of the HPF, and a portion indicated by an arrow Q12 indicates a phase characteristic of the frequency characteristics of the HPF.

In particular, the vertical axis in the amplitude characteristics indicates gain (amplitude), and the horizontal axis indicates frequency. Further, in the phase characteristics, the vertical axis indicates the phase, and the horizontal axis indicates the frequency. From this frequency characteristic, it can be seen that on the low-frequency side of the HPF, the gain is small and the phase is a positive value.

On the other hand, the portion indicated by arrow Q13 shows the impulse response of the HPF. The vertical axis of the impulse response indicates amplitude, and the horizontal axis indicates time, that is, time samples. Note that here, the impulse response of the HPF is an enlarged version of the vicinity of the 0th sample.

Such an impulse response can be used as an IIR type filter, and by convolving the impulse response shown by arrow Q13 with the audio signal, the HPF filtering process can be performed on the audio signal.

Furthermore, the frequency characteristics of the HPF, that is, the amplitude characteristics and the phase characteristics, and the impulse response of the HPF have a reversible relationship, although there is a conversion error.

Specifically, when IFFT is performed on a frequency characteristic consisting of an amplitude characteristic shown by arrow Q11 and a phase characteristic shown by arrow Q12, an impulse response shown by arrow Q13 is ideally obtained. On the other hand, when FFT is performed on the impulse response shown by arrow Q13, a frequency characteristic ideally consisting of an amplitude characteristic shown by arrow Q11 and a phase characteristic shown by arrow Q12 is obtained.

If such an impulse response of the HPF is convolved with the audio signal of the mastered content while playing the sound with the above-mentioned speaker, it is possible to add the same phase characteristics to the content sound as the speaker, but the low frequency The gain (amplitude) of the signal decreases.

Therefore, we actually performed FFT on the impulse response shown by arrow Q13, and the resulting frequency characteristics were made flat by setting the amplitude (gain) of all frequencies in the amplitude characteristics to 1, and then performed IFFT. Consider reconstructing the impulse response.

At this time, the impulse response to be obtained by reconstruction is an impulse response that adds only the phase characteristics shown in Figure 1 to the audio signal without changing the amplitude characteristics, that is, the impulse response that adds only the phase characteristics shown in Figure 1 to the audio signal without changing the amplitude characteristics. It is considered to be an impulse response that adds only phase characteristics.

Then, by convolving the impulse response obtained through reconstruction with the audio signal of the mastered content while playing the sound with the above-mentioned speaker, the phase characteristics of the target speaker can be adjusted without changing the amplitude characteristics. It can be added to the sound of the content. This allows the listener (user) to experience substantially the same sound as the sound produced by the creator in the mastering studio.

Note that hereinafter, the impulse response that functions as a filter that adds a desired phase characteristic without changing the amplitude characteristic will also be particularly referred to as a target phase characteristic impulse response.

When attempting to obtain a target phase characteristic impulse response by reconstructing the impulse response, it is conceivable to perform the reconstruction as shown in FIG. 2, for example.

In FIG. 2, the impulse response shown by arrow Q13 in FIG. 1 is shown in the portion shown by arrow Q21.

This impulse response converges after approximately 1024 samples. However, in this case, considering the tone after conversion, the 4096 process is performed by zero-filling the back side of the impulse response in the time direction, that is, the future side, as shown by arrow Q22.

In other words, 0 data, which is a sample with a sample value of 0, is added to the rear side (end) of the impulse response in the time direction. Make it a sample.

When FFT is performed on the impulse response zero-padded in this manner as shown by arrow Q23, amplitude characteristics and phase characteristics similar to those shown in FIG. 1 are obtained.

Here, the target phase characteristic impulse response that is aimed at is one in which the amplitude characteristic is flat or substantially flat, and the phase characteristic is the phase characteristic shown by arrow Q12.

Therefore, the amplitude (gain) value of each frequency in the amplitude characteristic obtained by FFT is adjusted to "1". In other words, the amplitude of the amplitude characteristic obtained by FFT is adjusted so as to have a flat amplitude characteristic.

Further, since the phase characteristic obtained by FFT should be the target phase characteristic shown by the arrow Q12, no particular phase adjustment is performed on the phase characteristic obtained by FFT.

Next, as shown by an arrow Q24, IFFT is performed on the frequency characteristic consisting of the flat amplitude characteristic obtained by amplitude adjustment and the phase characteristic obtained by FFT.

Furthermore, since the impulse response obtained by IFFT does not converge to 0, a fade process is performed to fade out the rear (tail side) of the impulse response in the time direction for the impulse response obtained by IFFT and converge to 0. will be held.

The impulse response is reconstructed by such fade processing, and as a result, the target phase characteristic impulse response shown by arrow Q25 is obtained. Here, an impulse response with a length of 4096 samples is obtained as the target phase characteristic impulse response.

The target phase characteristic impulse response shown by arrow Q25 should ideally have a flat or substantially flat amplitude characteristic and the same phase characteristic as the original HPF.

However, in reality, conversion distortion occurs in conversions such as FFT and IFFT, so the frequency characteristic of the target phase characteristic impulse response shown by arrow Q25 becomes as shown in FIG. 3.

In FIG. 3, a portion indicated by an arrow Q31 indicates an amplitude characteristic, and a portion indicated by an arrow Q32 indicates a phase characteristic. Note that the vertical axis in the amplitude characteristics indicates gain (amplitude), and the horizontal axis indicates frequency. Further, in the phase characteristics, the vertical axis indicates the phase, and the horizontal axis indicates the frequency.

In the part shown by arrow Q31, curve L11 shows the amplitude characteristic of the target phase characteristic impulse response shown by arrow Q25 in FIG. 2, and curve L12 shows the amplitude characteristic of the original HPF shown by arrow Q21 in FIG. There is. From the curve L11, in the amplitude characteristic of the target phase characteristic impulse response, the gain in the low frequency portion, that is, the portion shown by the arrow W11, has decreased, although not as much as in the original HPF, and the amplitude characteristic is not flat. I understand.

Further, in the part indicated by arrow Q32, curve L13 indicates the phase characteristic of the target phase characteristic impulse response indicated by arrow Q25 in FIG. 2, and curve L14 indicates the phase characteristic of the original HPF indicated by arrow Q21 in FIG. In other words, it shows the target phase characteristics.

In this example, the curve L13 is substantially the same as the curve L14, and it can be seen that the target phase characteristic is obtained in the target phase characteristic impulse response.

By the way, in general, when the target phase characteristic impulse response is opposite, that is, when the phase characteristic is flat (straight line) and the amplitude (gain) changes, the impulse response basically has a symmetrical shape. It has been known.

Therefore, the applicant performed zero padding processing so that the impulse response was approximately symmetrical around the rising part of the pulse, so that the sections before and after the rising part of the pulse were the same length. For example, we thought that it would be possible to obtain an impulse response with flat amplitude characteristics.

Here, perform FFT and IFFT on the original HPF impulse response by zero-filling it at least on the front side (past side) in the time direction so that the impulse response has a substantially symmetrical shape. Consider generating a target phase characteristic impulse response.

In such a case, for example, as shown in FIG. 4, the impulse response is reconstructed to generate a target phase characteristic impulse response.

In FIG. 4, the portion indicated by arrow Q41 shows the impulse response of the HPF indicated by arrow Q13 in FIG. 1, and this impulse response converges at approximately 1024 samples.

In this example, zero padding processing is performed as shown by arrow Q42 on the impulse response of the HPF shown by arrow Q41.

That is, according to the length of the impulse response, 0 data is added not only to the rear side (tail side) of the impulse response in the time direction but also to the front side (head side).

In particular, here, 0 data is added for 8192 samples to the front side of the impulse response in the time direction, and 0 data is also added to the rear side of the impulse response in the time direction so that the impulse length itself is 8192 samples long. It has been added. Due to this zero-filling process, the impulse response shown by the arrow Q42 has a substantially symmetrical shape, and the total length is 16384 samples.

Next, as shown by arrow Q43, when FFT is performed on the zero-padded impulse response, amplitude characteristics and phase characteristics are obtained as in the case of arrow Q23 in FIG.

In this example as well, the target amplitude characteristic of the target phase characteristic impulse response is flat, so the amplitude (gain) value of each frequency in the amplitude characteristic obtained by FFT is adjusted to "1", making it flat. It is considered to be an amplitude characteristic.

Further, since the phase characteristics obtained by FFT should be the target phase characteristics, no particular phase adjustment is performed on the phase characteristics obtained by FFT.

Next, as shown by arrow Q44, IFFT is performed on the frequency characteristic consisting of the flat amplitude characteristic obtained by amplitude adjustment and the phase characteristic obtained by FFT, and the impulse response obtained as a result is A fade process is performed in the same manner as in the case of arrow Q24 in FIG.

The impulse response obtained by the fade processing is then set as the target phase characteristic impulse response. Here, the target phase characteristic impulse response shown by arrow Q45 is obtained, and this target phase characteristic impulse response has a shape that is nearly symmetrical. Furthermore, the length of the target phase characteristic impulse response is 16384 samples.

The frequency characteristic of the target phase characteristic impulse response indicated by the arrow Q45 obtained in this manner is as shown in FIG.

In FIG. 5, a portion indicated by an arrow Q51 indicates an amplitude characteristic, and a portion indicated by an arrow Q52 indicates a phase characteristic. Note that the vertical axis in the amplitude characteristics indicates gain (amplitude), and the horizontal axis indicates frequency. Further, in the phase characteristics, the vertical axis indicates the phase, and the horizontal axis indicates the frequency.

In the part shown by arrow Q51, curve L31 shows the amplitude characteristic of the target phase characteristic impulse response shown by arrow Q45 in FIG. 4, and curve L32 shows the amplitude characteristic of the original HPF shown by arrow Q41 in FIG. There is.

It can be seen that in the amplitude characteristic of the target phase characteristic impulse response shown by the curve L31, the amplitude (gain) value at each frequency falls within a range of ±0.2 dB, and a substantially flat characteristic is obtained. That is, it can be seen that the target amplitude characteristics are obtained.

Further, in the part shown by arrow Q52, curve L33 shows the phase characteristic of the target phase characteristic impulse response shown by arrow Q45 in FIG. 4, and curve L34 shows the phase characteristic of the original HPF shown by arrow Q41 in FIG. In other words, it shows the target phase characteristics. Furthermore, curve L35 shows the phase characteristic of a simple impulse delayed by 8192 samples, that is, the linear phase.

Here, the curve L33 and the curve L34 almost overlap, and it can be seen that the phase characteristics of the target phase characteristic impulse response are substantially equivalent to the target characteristics.

Further, curve L35 is shown for comparison. Since the curve L35 shows the phase characteristic of a simple impulse with a linear phase, the difference between the curve L33 and the curve L35 at each frequency becomes the phase value at each frequency of the phase characteristic shown by the arrow Q12 in FIG. If so, it means that the target characteristic is obtained as the phase characteristic of the target phase characteristic impulse response. Note that the phase characteristic of the original HPF shown by arrow Q41 in FIG. 4 is the same as the phase characteristic shown by arrow Q12 in FIG.

In this example, when comparing curve L33 and curve L35, the difference in phase between them becomes smaller as the frequency becomes higher. Therefore, it can be seen from the curve L33 and the curve L35 that substantially the same characteristic as the phase characteristic shown by the arrow Q12 in FIG. 1 is obtained as the phase characteristic of the target phase characteristic impulse response.

From the above, it is possible to perform zero-filling processing at least on the front side in the time direction for an impulse response that has the target phase characteristics, and perform FFT, IFFT, and fade processing on the zero-padded impulse response. It can be seen that a target phase characteristic impulse response having a flat or substantially flat amplitude characteristic and a target phase characteristic can be obtained.

The method of generating the target phase characteristic impulse response described above with reference to FIG. 4 is the method A1 described above.

In addition, when generating the target phase characteristic impulse response, the longer the length of the zero-padded impulse response, that is, the greater the number of samples, the closer the frequency characteristic of the target phase characteristic impulse response will be to the target characteristic. . In other words, better characteristics can be obtained. In particular, when the length of the zero-padded impulse response becomes infinite samples, the error between the frequency characteristic of the target phase characteristic impulse response and the target characteristic becomes extremely close to zero.

Furthermore, when generating a target phase characteristic impulse response, it may be desirable to reduce the amount of processing even if some error from the target characteristic is allowed. For example, if the length of the target phase characteristic impulse response is shortened, the amount of processing will be reduced both during generation and during convolution after generation.

In such a case, for example, as shown in Fig. 6, by reducing the number of 0 data added to the impulse response in the 0-filling process, the amount of processing can be reduced and a target phase characteristic impulse response with sufficient characteristics can be obtained. It's okay.

In FIG. 6, the portion indicated by arrow Q61 shows the impulse response of the HPF indicated by arrow Q13 in FIG. 1, and this impulse response converges at approximately 1024 samples.

In this example, zero padding processing is performed as shown by arrow Q62 on the impulse response of the HPF shown by arrow Q61.

Here, 0 data is added for 384 samples to the front side of the impulse response in the time direction, and 0 data is also added to the rear side of the impulse response in the time direction so that the entire length of the impulse response is 4096 samples. has been done.

In this zero-filling process, since the number of zero data added to the front side of the impulse response in the time direction is small, the impulse response after the zero-filling process shown by arrow Q62 does not have a symmetrical shape.

Next, as shown by arrow Q63, when FFT is performed on the zero-padded impulse response, amplitude characteristics and phase characteristics are obtained as in the case of arrow Q23 in FIG.

In this example, as in the case in Fig. 4, the amplitude (gain) value of each frequency in the amplitude characteristic obtained by FFT is adjusted to "1" to make a flat amplitude characteristic, and the phase characteristic obtained by FFT is No particular phase adjustment is performed for .

Next, as shown by arrow Q64, IFFT is performed on the frequency characteristic consisting of the flat amplitude characteristic obtained by amplitude adjustment and the phase characteristic obtained by FFT, and the impulse response obtained as a result is A fade process is performed in the same manner as in the case of arrow Q24 in FIG.

The impulse response obtained by the fade processing is then set as the target phase characteristic impulse response. Here, the target phase characteristic impulse response shown by arrow Q65 is obtained, and the length of the target phase characteristic impulse response is 4096 samples.

Note that in this example, since the number of 0 data added to the front side of the impulse response in the time direction is small, the target phase characteristic impulse response shown by arrow Q65 does not have a symmetrical shape.

The frequency characteristic of the target phase characteristic impulse response obtained in this way and indicated by the arrow Q65 is as shown in FIG.

In FIG. 7, a portion indicated by an arrow Q71 indicates an amplitude characteristic, and a portion indicated by an arrow Q72 indicates a phase characteristic. Note that the vertical axis in the amplitude characteristics indicates gain (amplitude), and the horizontal axis indicates frequency. Further, in the phase characteristics, the vertical axis indicates the phase, and the horizontal axis indicates the frequency.

In the part shown by arrow Q71, curve L51 shows the amplitude characteristic of the target phase characteristic impulse response shown by arrow Q65 in FIG. 6, and curve L52 shows the amplitude characteristic of the original HPF shown by arrow Q61 in FIG. There is.

It can be seen that the amplitude characteristic of the target phase characteristic impulse response shown by the curve L51 has an amplitude (gain) value at each frequency within a range of ±1 dB, and a substantially flat characteristic is obtained. That is, it can be seen that sufficient amplitude characteristics are obtained.

In particular, here, the amplitude characteristic shown by curve L51 has a large error from the target characteristic when compared with the amplitude characteristic shown by curve L31 in FIG. 5, but the error is within a sufficiently small range. I know that there is.

Further, in the part shown by arrow Q72, curve L53 shows the phase characteristic of the target phase characteristic impulse response shown by arrow Q65 in FIG. 6, and curve L54 shows the phase characteristic of the original HPF shown by arrow Q61 in FIG. In other words, it shows the target phase characteristics. Furthermore, the curve L55 shows the phase characteristics of a delayed simple impulse, similar to the curve L35 in FIG.

Here, the curve L53 and the curve L54 almost overlap, although the error is larger than in the case in FIG. 5, and it can be seen that the phase characteristic of the target phase characteristic impulse response has almost the same characteristic as the target characteristic. I understand.

Furthermore, when comparing the curve L53 and the curve L55, the difference in their phase becomes smaller as the frequency increases, and as in the case in FIG. 5, the arrow Q12 in FIG. 1 is used as the phase characteristic of the target phase characteristic impulse response. It can be seen that almost the same characteristics as the phase characteristics shown in Figure 1 are obtained.

As described above, even if the number of 0 data added to the front side of the impulse response in the time direction that has the target phase characteristic is reduced to a certain extent, the amplitude characteristic is flat or almost flat, and the target phase characteristic is still maintained. A target phase characteristic impulse response can be obtained.

The amount of 0 data to be added to the front side of the impulse response in the time direction is a trade-off between the tolerance for the target characteristics and the amount of processing, so the number of 0 data to be added can be adjusted as needed. You can adjust it accordingly.

Moreover, instead of performing zero-filling processing on an impulse response having a target phase characteristic, for example, zero-filling processing is performed on a simple impulse as shown in curve L35 in FIG. 5 to generate a target phase characteristic impulse response. You may. A method of generating such a target phase characteristic impulse response is method A2 described above.

In method A2, 0 padding processing is performed to add 0 data to the front side of the simple impulse in the time direction, and FFT is performed on the simple impulse after the 0 padding processing.

Note that, hereinafter, the phase characteristic of the frequency characteristic obtained by FFT for the simple impulse after the zero-filling process will also be particularly referred to as the phase characteristic of the simple impulse.

Furthermore, in method A2, zero padding processing is not performed on the impulse response having the target phase characteristic, and FFT is performed on the impulse response as it is. Hereinafter, the phase characteristic of the frequency characteristic obtained by FFT for the impulse response having the target phase characteristic will also be particularly referred to as the target phase characteristic.

Once the phase characteristics of a simple impulse and the target phase characteristics are obtained by FFT in this way, the phase characteristics of those simple impulses and the target phase characteristics are added, and the phase characteristics obtained by the addition and the flat amplitude IFFT is performed on the frequency characteristics consisting of the characteristics.

Then, fade processing is performed on the impulse response obtained by IFFT, and the impulse response obtained as a result is set as the target phase characteristic impulse response.

The target phase characteristic impulse response obtained in this manner is an impulse response that has a flat or substantially flat amplitude characteristic and a target phase characteristic.

In addition, in method A2, instead of adding the phase characteristics of the simple impulse and the target phase characteristic, if the target phase characteristic is subtracted from the phase characteristic of the simple impulse, the impulse response having the opposite characteristic of the target phase characteristic can be calculated as the target phase characteristic. It can be obtained as a characteristic impulse response.

Specifically, for example, the phase characteristics obtained by performing FFT on the impulse response of a predetermined HPF without performing zero-filling processing are subtracted from the phase characteristics of a simple impulse, and the resulting phase characteristics and , IFFT is performed on a frequency characteristic consisting of a flat amplitude characteristic. Then, fade processing is performed on the impulse response obtained by IFFT, and the impulse response obtained as a result is set as the target phase characteristic impulse response.

In this case, the phase characteristic of the obtained target phase characteristic impulse response becomes the inverse characteristic of the phase characteristic of the original HPF.

As described above, in method A1, an impulse response having a target phase characteristic is subjected to zero-filling processing, and then FFT, IFFT, and fade processing are performed to generate a target phase characteristic impulse response. On the other hand, in method A2, a simple impulse is subjected to 0-filling processing, and then FFT, IFFT, and fade processing are performed to generate a target phase characteristic impulse response.

The impulse response used in method A1 and the simple impulse used in method A2 are both impulse information, that is, information regarding impulses. Therefore, when method A1 and method A2 are generalized, zero-filling processing is performed on the impulse information, FFT, IFFT, and fade processing are performed on the phase characteristics obtained as a result, and the target phase characteristic impulse is It can be said that a response is generated.

By using the target phase characteristic impulse response obtained as described above, it is possible to add a desired phase characteristic to an audio signal without changing the amplitude characteristic.

As a specific example, consider a case in which there is content that has been mastered while playing back sound through a mastering speaker, and the content is played back through headphones or speakers on the playback side.

In this case, by convolving the audio signal of the content with a target phase characteristic impulse response that has characteristics opposite to the phase characteristics of the headphones or speakers on the playback side, the phase characteristics of the headphones or speakers on the playback side can be canceled for the audio signal of the content. I can do it. Here, an audio signal in which the phase characteristics of headphones or speakers on the playback side have been canceled will be referred to as a corrected audio signal.

Note that the target phase characteristic impulse response having a characteristic opposite to the phase characteristic of the headphones or speakers on the reproduction side may be generated by the method A2 or method A1 described above. For example, when generating such a target phase characteristic impulse response using method A1, zero-filling is performed on the impulse response having a phase characteristic opposite to that of the reproduction side headphones or speakers, and FFT, IFFT, and fade processing are performed. Just go.

Furthermore, by convolving the corrected audio signal with a target phase characteristic impulse response that has the same characteristics as the phase characteristics of the mastering speaker, the phase characteristics of the mastering speaker can be adjusted for the corrected audio signal, that is, for the sound of the content. can be added.

Therefore, if the sound of the content is played back based on the corrected audio signal to which the phase characteristics of the mastering speaker have been added in this way, the listener ( (user) can experience it.

In addition, for example, when a listener plays the sound of a content using headphones on the playback side, it is possible to use head-related transfer characteristics (HRTF (Head Related Transfer Function)) to help the creator in the mastering studio. This makes it possible to present a sound that is closer to the sound that is being produced.

Here, HRTF is a function indicating the transmission characteristics of sound from the sound source to the listener's ears, more specifically to the vicinity of the listener's eardrum or the entrance of the ear canal.

In this example, by convolving the corrected audio signal with the phase characteristics of the mastering speakers and the HRTF, the listener will experience a sound that is closer to the sound that the creator heard while producing in the mastering studio. can be done.

<Example of configuration of impulse response generation device>
Next, the specific configuration and operation of the impulse response generation device that generates the target phase characteristic impulse response described above will be explained.

FIG. 8 is a diagram illustrating a configuration example of an impulse response generation device that generates a target phase characteristic impulse response, that is, an impulse response whose amplitude characteristic is flat or approximately flat and has a desired phase characteristic by the method A1 described above. .

The impulse response generation device 11 shown in FIG. 8 includes a zero padding processing section 21, an FFT processing section 22, an IFFT processing section 23, and a fade processing section 24.

The zero padding processing unit 21 is supplied with an impulse response having a target phase characteristic, which is used to generate a target phase characteristic impulse response. In the following, an impulse response having such a target phase characteristic will be referred to as an input impulse response.

The zero padding processing section 21 performs zero padding processing on the supplied input impulse response and supplies the result to the FFT processing section 22 .

The FFT processing unit 22 performs FFT on the zero-padded input impulse response supplied from the zero-filling processing unit 21 and supplies the phase characteristics of the frequency characteristics obtained as a result to the IFFT processing unit 23. .

The IFFT processing unit 23 is supplied with a flat amplitude characteristic (gain characteristic) in which the gain (amplitude) of each frequency is "1" from the outside.

The IFFT processing section 23 performs IFFT on the frequency characteristics consisting of the flat amplitude characteristics supplied from the outside and the phase characteristics supplied from the FFT processing section 22, and applies the resulting impulse response to the fade processing section. 24. In other words, IFFT is performed based on the flat amplitude characteristic and the phase characteristic supplied from the FFT processing section 22, and an impulse response is generated.

Note that the IFFT processing section 23 does not use a flat amplitude characteristic supplied from the outside, but performs gain adjustment on the amplitude characteristic of the frequency characteristic obtained by FFT in the FFT processing section 22 to obtain a flat amplitude. A characteristic may be generated and the amplitude characteristic may be used for IFFT.

The fade processing unit 24 performs a fade process on the impulse response supplied from the IFFT processing unit 23, and outputs the resulting impulse response as a target phase characteristic impulse response.

<Explanation of impulse response generation processing>
Next, the operation of the impulse response generation device 11 will be explained.

That is, the impulse response generation process performed by the impulse response generation device 11 will be described below with reference to the flowchart of FIG.

In step S<b>11 , the zero padding processing unit 21 performs zero padding processing on the supplied input impulse response and supplies the result to the FFT processing unit 22 .

For example, in step S11, as described with reference to FIGS. 4 and 6, zero padding processing is performed to add zero data to the rear and front sides of the input impulse response in the time direction. In the zero filling process, zero data is added at least to the front side of the input impulse response in the time direction.

In step S12, the FFT processing section 22 performs FFT on the input impulse response after the zero padding process supplied from the zero padding processing section 21, and converts the phase characteristic of the frequency characteristics obtained as a result to the IFFT processing section 22. supply to.

In step S13, the IFFT processing section 23 performs IFFT on the frequency characteristic consisting of the flat amplitude characteristic supplied from the outside and the phase characteristic supplied from the FFT processing section 22, and calculates the impulse response obtained as a result. The signal is supplied to the fade processing section 24.

In step S14, the fade processing unit 24 performs a fade process on the impulse response supplied from the IFFT processing unit 23, and outputs the resulting impulse response as a target phase characteristic impulse response.

For example, in fade processing, the target phase characteristic impulse response is generated by fading out the rear side (tail side) in the time direction of the impulse response supplied from the IFFT processing unit 23 and converging it to 0. Note that if the impulse response obtained by IFFT converges to 0, no particular fade processing is necessary.

Furthermore, if an impulse response having, for example, a phase characteristic opposite to that of headphones is used as the input impulse response, the phase characteristic of the headphones can be canceled as the target phase characteristic impulse response, that is, an impulse response having characteristics opposite to the phase characteristic of headphones can be obtained. be able to.

Once the target phase characteristic impulse response is generated in this way, the impulse response generation process ends.

As described above, the impulse response generation device 11 performs zero padding processing that adds zero data to at least the front side of the input impulse response in the time direction, and performs FFT, IFFT, and fade processing on the zero padded input impulse response. By performing the processing, a target phase characteristic impulse response is generated.

By doing so, it is possible to obtain a target phase characteristic impulse response that functions as a filter to which a target phase characteristic can be added without changing the amplitude characteristic. This makes it possible to obtain a desired phase characteristic using the target phase characteristic impulse response without changing the amplitude characteristic.

<Second embodiment>
<Example of configuration of impulse response generation device>
Furthermore, when generating the target phase characteristic impulse response using the method A2 described above, the impulse response generation apparatus is configured as shown in FIG. 10, for example. Note that in FIG. 10, parts corresponding to those in FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

The impulse response generation device 51 shown in FIG. 10 includes an FFT processing section 61, a zero padding processing section 62, an FFT processing section 63, an arithmetic processing section 64, an IFFT processing section 23, and a fade processing section 24. The configuration of this impulse response generation device 51 is such that an FFT processing section 61 to an arithmetic processing section 64 are provided in place of the zero padding processing section 21 and FFT processing section 22 in the impulse response generation device 11.

The FFT processing unit 61 is supplied with an impulse response having a target phase characteristic, that is, an input impulse response, which is used to generate the target phase characteristic impulse response.

The FFT processing section 61 performs FFT on the supplied input impulse response, and supplies the phase characteristic of the frequency characteristics obtained as a result to the arithmetic processing section 64 . Note that if the target phase characteristic itself can be obtained and the target phase characteristic can be supplied to the arithmetic processing section 64, it is not necessary to provide the FFT processing section 61 in particular.

The zero padding processing section 62 is supplied with simple impulses used to generate the target phase characteristic impulse response. The zero padding processing section 62 performs zero padding processing on the supplied simple impulse and supplies it to the FFT processing section 63 .

The FFT processing unit 63 performs FFT on the zero-padded simple impulse supplied from the zero-padding processing unit 62, and supplies the phase characteristic of the frequency characteristics obtained as a result to the arithmetic processing unit 64.

The calculation processing unit 64 performs calculation processing based on the phase characteristics supplied from the FFT processing unit 61 and the phase characteristics supplied from the FFT processing unit 63, and supplies the resulting phase characteristics to the IFFT processing unit 23. do. Here, addition processing or subtraction processing is performed as the arithmetic processing.

<Explanation of impulse response generation processing>
Next, the operation of the impulse response generation device 51 will be explained.

That is, the impulse response generation process performed by the impulse response generation device 51 will be described below with reference to the flowchart of FIG.

In step S41, the FFT processing section 61 performs FFT on the supplied input impulse response, and supplies the phase characteristic of the frequency characteristics obtained as a result to the arithmetic processing section 64.

In step S<b>42 , the zero padding processing unit 62 performs zero padding processing on the supplied simple impulse and supplies the result to the FFT processing unit 63 . In the 0-filling process, 0 data is added to the front side of the simple impulse in the time direction, and the simple impulse is appropriately delayed.

In step S43, the FFT processing unit 63 performs FFT on the simple impulse after the zero-filling process supplied from the zero-filling processing unit 62, and sends the phase characteristic of the frequency characteristics obtained as a result to the arithmetic processing unit 64. supply

In step S44, the arithmetic processing section 64 performs arithmetic processing based on the phase characteristics supplied from the FFT processing section 61 and the phase characteristics supplied from the FFT processing section 63, and transfers the obtained phase characteristics to the IFFT processing section. 23.

For example, when trying to obtain the same phase characteristic of the input impulse response as the phase characteristic of the target phase characteristic impulse response, the arithmetic processing section 64 uses the phase characteristic of the input impulse response supplied from the FFT processing section 61. and the phase characteristic of the simple impulse after zero-filling processing, which is supplied from the FFT processing section 63 , and the resulting phase characteristic is supplied to the IFFT processing section 23 .

On the other hand, when attempting to obtain the inverse characteristic of the phase characteristic of the input impulse response as the phase characteristic of the target phase characteristic impulse response, the arithmetic processing section 64 calculates the input impulse response supplied from the FFT processing section 61. is subtracted from the phase characteristic of the zero-padded simple impulse supplied from the FFT processing section 63, and the resulting phase characteristic is supplied to the IFFT processing section 23.

When addition or subtraction is performed as the arithmetic processing for the phase characteristics in this way, the processes of step S45 and step S46 are performed and the impulse response generation process ends, but these processes are performed in step S13 and step S46 of FIG. Since it is the same as the process in S14, its explanation will be omitted.

As described above, the impulse response generation device 51 performs zero padding processing to add zero data to the front side of the simple impulse in the time direction, and based on the zero padded simple impulse response and the input impulse response, the impulse response generation device 51 performs a target phase. Generate a characteristic impulse response.

By doing so, it is possible to obtain a target phase characteristic impulse response that functions as a filter to which a target phase characteristic can be added without changing the amplitude characteristic. This makes it possible to obtain a desired phase characteristic using the target phase characteristic impulse response without changing the amplitude characteristic.

<Third embodiment>
<Example of configuration of playback device>
Here, a reproduction device that reproduces content using the target phase characteristic impulse response generated by the impulse response generation device 11 or the impulse response generation device 51 described above will be described.

In the following, in order to make the explanation more concrete, it is assumed that the content to be played back has been mastered in a predetermined studio as shown in FIG. 12.

In the example shown in FIG. 12, there is a producer M11 who performs mastering in the studio, and the producer M11 adjusts the amplitude of each band of the content while playing back the sound of the content using the speaker 91 arranged in the studio. This is done as mastering work.

Furthermore, the audio signal of the content obtained through mastering is played back by a playback system including a playback device owned by the listener. Although any device such as headphones, speakers, or earphones may be used to reproduce the sound of the content, the following description will continue assuming that headphones are used as a specific example.

A reproducing device used for reproducing content is configured as shown in FIG. 13, for example.

In the example shown in FIG. 13, the playback device 121 includes at least a portable player, a smartphone, a personal computer, etc. that can control the playback of audio content, and headphones 122 are connected to the playback device 121.

The playback device 121 includes an acquisition section 131, a speaker phase characteristic convolution section 132, and a playback control section 133.

In the playback device 121, the audio signal of the content obtained by mastering by the producer M11 is supplied to the speaker phase characteristic convolution unit 132.

The acquisition unit 131 acquires and holds the target phase characteristic impulse response from an external device such as the impulse response generation device 11 or the impulse response generation device 51 at an arbitrary timing. Further, the acquisition unit 131 supplies the held target phase characteristic impulse response to the speaker phase characteristic convolution unit 132.

The target phase characteristic impulse response acquired by the acquisition unit 131 is generated by the impulse response generation device 11 or the impulse response generation device 51 using an input impulse response having the phase characteristic of the speaker 91 used for mastering. It is. That is, the target phase characteristic impulse response is an impulse response having the same phase characteristic as the phase characteristic of the speaker 91.

Note that the target phase characteristic impulse response may not be acquired by the acquisition unit 131 at an arbitrary timing, but may be held in the acquisition unit 131 in advance.

Furthermore, hereinafter, the target phase characteristic impulse response having the same phase characteristic as the phase characteristic of the speaker 91 will also be particularly referred to as a speaker characteristic impulse response.

The speaker phase characteristic convolution section 132 convolves the speaker characteristic impulse response supplied from the acquisition section 131 with the supplied audio signal, and supplies the resulting audio signal to the reproduction control section 133.

The reproduction control section 133 supplies the audio signal supplied from the speaker phase characteristic convolution section 132 to the headphones 122, and causes the sound of the content to be reproduced. In other words, the playback control unit 133 controls the playback of the sound of the content on the headphones 122.

The headphones 122 reproduce the sound of the content based on the audio signal supplied from the reproduction control section 133.

Although the playback device 121 is not provided with the headphone 122 here, the headphone 122 may be provided in the playback device 121, or the acquisition unit 131 or playback control may be provided inside the headphone 122. A portion 133 may be provided.

<Explanation of playback process>
Next, the operation of the playback device 121 will be explained. That is, the reproduction processing by the reproduction device 121 will be described below with reference to the flowchart of FIG. Note that at the timing when this reproduction process is started, the speaker characteristic impulse response has already been acquired by the acquisition unit 131.

In step S71, the speaker phase characteristic convolution section 132 convolves the speaker characteristic impulse response supplied from the acquisition section 131 with the supplied audio signal, and supplies the resulting audio signal to the reproduction control section 133.

Thereby, the phase characteristic of the speaker characteristic impulse response, that is, the phase characteristic of the speaker 91 can be added to the sound of the content based on the audio signal.

In step S72, the reproduction control unit 133 supplies the audio signal supplied from the speaker phase characteristic convolution unit 132 to the headphones 122 to reproduce the sound of the content, and the reproduction process ends.

Since the sound of the content reproduced by the headphones 122 has the same characteristics as the phase characteristics of the speaker 91, the listener who is listening to the sound of the content can hear the content that the producer M11 was listening to in the studio. I'm hearing a sound with almost the same quality as the sound. Moreover, since the speaker characteristic impulse response can add only a desired phase characteristic to the sound of the content without changing the amplitude characteristic, the gain of the sound of the content does not change.

As described above, the playback device 121 plays back the sound of the content after convolving the speaker characteristic impulse response with the audio signal of the content. By doing so, even when the sound of the content is played back using the headphones 122, the phase characteristics of the speaker 91 used for mastering can be added to the sound of the content. That is, desired phase characteristics can be obtained.

<Fourth embodiment>
<Example of configuration of playback device>
It has been explained that the playback device 121 adds the same characteristics as the phase characteristics of the speaker 91 to the sound of the content. However, when the sound of the content is played back with the headphones 122, the phase characteristics of the headphones 122 are also added to the sound.

Therefore, by not only adding the same characteristics as the phase characteristics of the speaker 91 to the sound of the content, but also canceling (removing) the phase characteristics of the headphones 122, the sound of the content that the creator M11 was listening to in the studio can be made to be closer to the sound of the content. The sound may be made to be audible to the listener.

In such a case, the playback device is configured as shown in FIG. 15, for example. Note that in FIG. 15, parts corresponding to those in FIG. 13 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

Headphones 122 are connected to the playback device 161 shown in FIG. Furthermore, the playback device 161 includes an acquisition section 131 , a headphone inverse characteristic convolution section 171 , a speaker phase characteristic convolution section 132 , and a playback control section 133 .

In particular, the configuration of the playback device 161 is such that a headphone inverse characteristic convolution section 171 is provided before the speaker phase characteristic convolution section 132 in the playback device 121.

In the reproduction device 161, the acquisition unit 131 acquires not only the speaker characteristic impulse response described above but also a target phase characteristic impulse response having a characteristic opposite to the phase characteristic of the headphones 122. Retrieved from an external device and maintained. Hereinafter, the target phase characteristic impulse response having a characteristic opposite to that of the headphone 122 will also be particularly referred to as a headphone reverse characteristic impulse response.

This headphone inverse characteristic impulse response is, for example, a target phase characteristic impulse response generated by the impulse response generation device 51 by using an input impulse response having a phase characteristic of the headphones 122 and performing subtraction as a calculation process in the calculation processing unit 64. It is.

Note that the headphone inverse characteristic impulse response may also be stored in advance in the acquisition unit 131 instead of being acquired by the acquisition unit 131.

The acquisition unit 131 supplies the held headphone inverse characteristic impulse response to the headphone inverse characteristic convolution unit 171 .

The headphone inverse characteristic convolution unit 171 convolves the headphone inverse characteristic impulse response supplied from the acquisition unit 131 with the audio signal of the supplied content, and supplies the resulting audio signal to the speaker phase characteristic convolution unit 132. do.

<Explanation of playback process>
Next, the operation of the playback device 161 will be explained. That is, the reproduction processing by the reproduction device 161 will be described below with reference to the flowchart of FIG. 16. Note that at the timing when this reproduction process is started, the speaker characteristic impulse response and the headphone inverse characteristic impulse response have already been acquired by the acquisition unit 131.

In step S101, the headphone inverse characteristic convolution section 171 convolves the headphone inverse characteristic impulse response supplied from the acquisition section 131 with the audio signal of the supplied content, and the resulting audio signal is transferred to the speaker phase characteristic convolution section. 132.

Thereby, it is possible to add a phase characteristic opposite to the phase characteristic of the headphones 122 to the sound of the content. In other words, the phase characteristics of the headphones 122 that are added when the sound of the content is reproduced with the headphones 122 are canceled. Moreover, by convolution of the headphone inverse characteristic impulse response, only the phase characteristic can be adjusted without changing the amplitude (gain) of the sound of the content.

When the headphone inverse characteristic impulse response is convolved with the audio signal, the processing of steps S102 and S103 is then performed and the playback processing ends, but these processings are the same as the processing of steps S71 and S72 in FIG. Since it is the same as that, its explanation will be omitted.

When the playback device 161 plays back the sound of the content, first, the phase characteristics of the headphones 122 are canceled for the sound of the content, and then the phase characteristics of the speaker 91, which are the characteristics to be added, are added.

Note that a target phase characteristic impulse response is generated to which an inverse characteristic of the phase characteristic of the headphones 122 and a phase characteristic of the speaker 91 can be added at the same time, and the target phase characteristic impulse response is convolved with the audio signal of the content. It's okay.

However, by separately convolving the speaker characteristic impulse response and the headphone inverse characteristic impulse response like the playback device 161, it is possible to freely change the phase characteristic added to the sound of the content. That is, for example, in the playback device 161, it is possible to select an arbitrary speaker 91 from among a plurality of speakers 91 made by different manufacturers, etc., and convolve a speaker characteristic impulse response having the phase characteristic of the selected speaker 91. .

As described above, the playback device 161 convolves the headphone inverse characteristic impulse response into the audio signal of the content, further convolves the speaker characteristic impulse response into the audio signal, and then reproduces the sound of the content.

By doing this, even when the sound of the content is played back with the headphones 122, the phase characteristics added by the headphones 122 are canceled and the phase characteristics of the speaker 91 used for mastering are added to the sound of the content. can do. That is, desired phase characteristics can be obtained. In particular, in the playback process described with reference to FIG. 16, it is possible to hear a sound that is closer to the sound of the content that the creator M11 was listening to in the studio than in the playback process described with reference to FIG. .

<Fifth embodiment>
<Example of configuration of playback device>
Note that when the sound of the content is played back through the headphones 122, by convolving the HRTF that indicates the transmission characteristics of the sound from the sound source, for example, the speaker 91 to the creator M11, the sound of the content that the creator M11 was listening to in the studio can be reproduced. I can hear the sound. In other words, it is possible to reproduce the studio listening environment at the time of mastering.

When convolving the HRTF with the audio signal of the content, the playback device is configured as shown in FIG. 17, for example. Note that in FIG. 17, parts corresponding to those in FIG. 15 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

Headphones 122 are connected to the playback device 201 shown in FIG. The playback device 201 also includes an acquisition section 131 , a headphone inverse characteristic convolution section 171 , a speaker phase characteristic convolution section 132 , an HRTF convolution section 211 , and a playback control section 133 .

In particular, the configuration of the reproducing device 201 is such that the HRTF convolution section 211 is provided after the speaker phase characteristic convolution section 132 in the reproduction device 161.

In the reproduction device 201, not only the above-mentioned speaker characteristic impulse response and headphone inverse characteristic impulse response but also the HRTF is acquired from an external device by the acquisition unit 131 and held. Note that the HRTF may also be stored in advance in the acquisition unit 131 instead of being acquired by the acquisition unit 131.

The acquisition unit 131 supplies the held HRTF to the HRTF convolution unit 211.

The HRTF convolution section 211 convolves the HRTF supplied from the acquisition section 131 with the audio signal supplied from the speaker phase characteristic convolution section 132, and supplies the resulting audio signal to the reproduction control section 133.

Note that the reproduction device 121 shown in FIG. 13 may be provided with the HRTF convolution unit 211.

<Explanation of playback process>
Next, the operation of the playback device 201 will be explained. That is, the reproduction processing by the reproduction device 201 will be described below with reference to the flowchart of FIG. 18. Note that at the timing when this reproduction process is started, the speaker characteristic impulse response, the headphone inverse characteristic impulse response, and the HRTF have already been acquired by the acquisition unit 131.

When the playback process is started, steps S131 and S132 are performed, but since these processes are the same as those of steps S101 and S102 in FIG. 16, their explanation will be omitted.

In step S133, the HRTF convolution unit 211 convolves the HRTF supplied from the acquisition unit 131 with the audio signal supplied from the speaker phase characteristic convolution unit 132, and supplies the resulting audio signal to the playback control unit 133. .

In step S134, the reproduction control unit 133 supplies the audio signal supplied from the HRTF convolution unit 211 to the headphones 122 to reproduce the sound of the content, and the reproduction process ends. As a result, when reproducing the sound of the content, the phase characteristics of the headphones 122 are canceled, and the phase characteristics of the speaker 91 and the sound transmission characteristics in the studio are added.

As described above, the playback device 201 plays back the sound of the content after convolving the headphone inverse characteristic impulse response, the speaker characteristic impulse response, and the HRTF into the audio signal.

By doing so, even when the sound of the content is played back with the headphones 122, the desired phase characteristics and the transfer characteristics in the desired listening environment such as a studio are added, and the sound that the creator M11 is listening to in the studio is added. Listeners can hear substantially the same sound as the content.

<Modified example>
<Example of configuration of playback device>
Note that a generation unit that generates the target phase characteristic impulse response may be provided inside the reproduction device 121, the reproduction device 161, and the reproduction device 201.

For example, when such a generating section is provided inside the playback device 161, the playback device 161 is configured as shown in FIG. Note that in FIG. 19, parts corresponding to those in FIG. 15 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

The reproduction device 161 shown in FIG. 19 includes a generation section 241, an acquisition section 131, a headphone inverse characteristic convolution section 171, a speaker phase characteristic convolution section 132, and a reproduction control section 133.

The configuration of the playback device 161 shown in FIG. 19 is such that the playback device 161 shown in FIG. 15 is further provided with a generation section 241.

The generation unit 241 corresponds to the impulse response generation device 11 and the impulse response generation device 51. That is, the generation unit 241 performs processing similar to the impulse response generation processing described with reference to FIGS. 9 and 11 to generate a headphone inverse characteristic impulse response and a speaker characteristic impulse response, and supplies them to the acquisition unit 131.

According to the present technology described in each of the above embodiments and modifications, only the phase characteristic can be adjusted without changing the amplitude characteristic, and a desired phase characteristic can be obtained.

For example, the phase characteristics of any speaker used for mastering in music production, especially the low-frequency phase characteristics, can be added to the sound source while the amplitude characteristics remain flat. As a result, even when playing back sound using headphones, it is possible to obtain a low-frequency sound quality effect equivalent to that obtained in a mastering studio.

Moreover, even if the target speaker is unknown, if the impulse response of any general IIR filter that imitates the phase characteristics of that speaker is used as the above-mentioned input impulse response, the obtained speaker characteristic impulse response can be used. By doing so, it is possible to add a low-frequency phase characteristic equivalent to that of a speaker without changing the amplitude characteristic.

Further, by adding an inverse characteristic of the phase characteristic of the headphones, especially the phase characteristic of the low frequency range, by the headphone inverse characteristic impulse response, it is possible to cancel the phase characteristic of the headphone, especially the phase characteristic of the low frequency range. After canceling the phase characteristics of the headphones, if the phase characteristics of the speaker, especially the low frequency characteristics, are added using the speaker characteristic impulse response, it is possible to obtain an effect closer to the low frequency sound quality effect in a mastering studio.

Note that if in the future it is possible to identify a speaker used in a mastering studio using metadata or the like, an impulse response having the phase characteristics of that speaker may be used as the input impulse response. Furthermore, if the speaker used in the mastering studio cannot be specified, an impulse response such as an IIR type HPF that imitates the phase characteristics of the speaker may be used as the input impulse response.

Furthermore, when playing the sound of content with headphones, in addition to canceling the phase characteristics of the headphones and adding the phase characteristics of the speakers, the HRTF is convolved with the audio signal of the content to improve the listening environment in the mastering studio. Low-frequency phase characteristics can be simulated using headphones.

<Computer configuration example>
By the way, the series of processes described above can be executed by hardware or software. When a series of processes is executed by software, the programs that make up the software are installed on the computer. Here, the computer includes a computer built into dedicated hardware and, for example, a general-purpose personal computer that can execute various functions by installing various programs.

FIG. 20 is a block diagram showing an example of a hardware configuration of a computer that executes the above-described series of processes using a program.

In a computer, a CPU (Central Processing Unit) 501, a ROM (Read Only Memory) 502, and a RAM (Random Access Memory) 503 are interconnected by a bus 504.

An input/output interface 505 is further connected to the bus 504. An input section 506 , an output section 507 , a recording section 508 , a communication section 509 , and a drive 510 are connected to the input/output interface 505 .

The input unit 506 includes a keyboard, a mouse, a microphone, an image sensor, and the like. The output unit 507 includes a display, a speaker, and the like. The recording unit 508 includes a hard disk, nonvolatile memory, and the like. The communication unit 509 includes a network interface and the like. The drive 510 drives a removable recording medium 511 such as a magnetic disk, an optical disk, a magneto-optical disk, or a semiconductor memory.

In the computer configured as described above, the CPU 501 executes the above-described series by, for example, loading a program recorded in the recording unit 508 into the RAM 503 via the input/output interface 505 and the bus 504 and executing it. processing is performed.

A program executed by the computer (CPU 501) can be provided by being recorded on a removable recording medium 511 such as a package medium, for example. Additionally, programs may be provided via wired or wireless transmission media, such as local area networks, the Internet, and digital satellite broadcasts.

In the computer, the program can be installed in the recording unit 508 via the input/output interface 505 by installing the removable recording medium 511 into the drive 510. Further, the program can be received by the communication unit 509 via a wired or wireless transmission medium and installed in the recording unit 508. Other programs can be installed in the ROM 502 or the recording unit 508 in advance.

Note that the program executed by the computer may be a program in which processing is performed chronologically in accordance with the order described in this specification, in parallel, or at necessary timing such as when a call is made. It may also be a program that performs processing.

Further, the embodiments of the present technology are not limited to the embodiments described above, and various changes can be made without departing from the gist of the present technology.

For example, the present technology can take a cloud computing configuration in which one function is shared and jointly processed by a plurality of devices via a network.

Moreover, each step explained in the above-mentioned flowchart can be executed by one device or can be shared and executed by a plurality of devices.

Furthermore, when one step includes multiple processes, the multiple processes included in that one step can be executed by one device or can be shared and executed by multiple devices.

Furthermore, the present technology can also have the following configuration.

(1)
an acquisition unit that acquires an impulse response having a flat or substantially flat amplitude characteristic and a predetermined phase characteristic;
and a phase characteristic convolution unit that convolves the impulse response with an input audio signal.
(2)
The audio signal processing device according to (1), wherein the predetermined phase characteristic is a phase characteristic that a predetermined speaker has.
(3)
The audio signal processing device according to (1) or (2), further comprising a playback control unit that controls playback of sound based on the audio signal obtained by convolution of the impulse response on headphones.
(4)
The audio signal processing device according to (3), further comprising an inverse characteristic convolution unit that convolves an impulse response having a characteristic opposite to the phase characteristic of the headphone into the input audio signal.
(5)
The audio signal processing device according to any one of (1) to (4), further comprising an HRTF convolution unit that convolves an HRTF into the audio signal obtained by convolution by the phase characteristic convolution unit.
(6)
The audio signal processing device according to any one of (1) to (5), further comprising an impulse response generation unit that generates the impulse response.
(7)
The audio signal processing device
Obtaining an impulse response that has flat or approximately flat amplitude characteristics and a predetermined phase characteristic,
An audio signal processing method comprising convolving the impulse response with an input audio signal.
(8)
Obtaining an impulse response that has flat or approximately flat amplitude characteristics and a predetermined phase characteristic,
A program that causes a computer to perform a process including the step of convolving the impulse response with an input audio signal.
(9)
An impulse response generation device that generates a target characteristic impulse response having a flat or substantially flat amplitude characteristic and a predetermined phase characteristic.
(10)
a zero padding processing unit that performs zero padding processing for adding zero data to predetermined impulse information;
an impulse information FFT processing unit that performs FFT on the impulse information to which the 0 data is added;
The impulse response generation device according to (9), further comprising: an IFFT processing unit that generates the target characteristic impulse response by performing IFFT based on the phase characteristic obtained by the FFT and the flat amplitude characteristic.
(11)
The impulse response generation device according to (10), wherein the zero padding processing unit adds the zero data to at least the front side of the impulse information in the time direction.
(12)
The impulse response generation device according to (10) or (11), further comprising a fade processing unit that performs a fade process on the impulse response obtained by the IFFT to obtain the target characteristic impulse response.
(13)
The impulse response generation device according to any one of (10) to (12), wherein the impulse information is an impulse response having the predetermined phase characteristic.
(14)
The impulse information is a simple impulse,
an impulse response FFT processing unit that performs FFT on the impulse response having the predetermined phase characteristic;
further comprising: an arithmetic processing unit that performs calculations based on the phase characteristics obtained by the FFT by the impulse information FFT processing unit and the phase characteristics obtained by the FFT by the impulse response FFT processing unit,
The impulse response generation device according to any one of (10) to (12), wherein the IFFT processing unit performs the IFFT based on the phase characteristic obtained by the calculation and the flat amplitude characteristic.
(15)
The calculation processing unit performs the calculation by adding the phase characteristics obtained by the FFT performed by the impulse information FFT processing unit and the phase characteristics obtained by the FFT performed by the impulse response FFT processing unit. (14) The impulse response generation device described in .
(16)
The arithmetic processing unit subtracts the phase characteristic obtained by the FFT by the impulse response FFT processing unit from the phase characteristic obtained by the FFT by the impulse information FFT processing unit as the calculation. (14) The impulse response generation device described in .
(17)
The impulse response generator is
An impulse response generation method for generating a target characteristic impulse response having a flat or substantially flat amplitude characteristic and a predetermined phase characteristic.
(18)
A program that causes a computer to execute processing including the step of generating a target characteristic impulse response having a flat or substantially flat amplitude characteristic and a predetermined phase characteristic.

Reference Signs List 11 Impulse response generation device, 21 Zero padding processing section, 22 FFT processing section, 23 IFFT processing section, 24 Fade processing section, 61 FFT processing section, 62 Zero padding processing section, 63 FFT processing section, 64 Arithmetic processing section, 121 Reproduction device, 131 acquisition unit, 132 speaker phase characteristic convolution unit, 133 playback control unit, 171 headphone inverse characteristic convolution unit, 211 HRTF convolution unit, 241 generation unit

Claims (9)

a zero padding processing unit that performs zero padding processing for adding zero data to predetermined impulse information;
an impulse information FFT processing unit that performs FFT on the impulse information to which the 0 data is added;
an IFFT processing unit that generates a target characteristic impulse response having a predetermined phase characteristic by performing IFFT based on the phase characteristic obtained by the FFT and the flat amplitude characteristic;
An impulse response generation device comprising : The zero padding processing unit adds the zero data to at least the front side of the impulse information in the time direction.
The impulse response generation device according to claim 1 . The apparatus further includes a fade processing unit that performs fade processing on the impulse response obtained by the IFFT to obtain the target characteristic impulse response.
The impulse response generation device according to claim 1 . The impulse information is an impulse response having the predetermined phase characteristic.
The impulse response generation device according to claim 1 . The impulse information is a simple impulse,
an impulse response FFT processing unit that performs FFT on the impulse response having the predetermined phase characteristic;
further comprising: an arithmetic processing unit that performs calculations based on the phase characteristics obtained by the FFT by the impulse information FFT processing unit and the phase characteristics obtained by the FFT by the impulse response FFT processing unit,
The IFFT processing unit performs the IFFT based on the phase characteristic obtained by the calculation and the flat amplitude characteristic.
The impulse response generation device according to claim 1 . The calculation processing unit performs the calculation by adding the phase characteristics obtained by the FFT performed by the impulse information FFT processing unit and the phase characteristics obtained by the FFT performed by the impulse response FFT processing unit.
The impulse response generation device according to claim 5 . The arithmetic processing unit subtracts the phase characteristic obtained by the FFT by the impulse response FFT processing unit from the phase characteristic obtained by the FFT by the impulse information FFT processing unit as the calculation.
The impulse response generation device according to claim 5 . The impulse response generator is
Performs 0 padding processing to add 0 data to predetermined impulse information,
performing FFT on the impulse information to which the 0 data has been added;
By performing IFFT based on the phase characteristics obtained by the FFT and the flat amplitude characteristics, a target characteristic impulse response having a predetermined phase characteristic is generated.
Impulse response generation method. Performs 0 padding processing to add 0 data to predetermined impulse information,
performing FFT on the impulse information to which the 0 data has been added;
A program that causes a computer to execute processing including a step of generating a target characteristic impulse response having a predetermined phase characteristic by performing IFFT based on the phase characteristic obtained by the FFT and the flat amplitude characteristic.

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