JP5958378B2 - Audio signal processing apparatus, control method and program for audio signal processing apparatus - Google Patents

Description

  The present invention relates to an audio signal processing device that emphasizes a specific frequency band component of an input audio signal, a control method for the audio signal processing device, and a program.

  Conventionally, as this type of technology, a frequency characteristic adjusting device that adjusts a frequency characteristic by selecting a desired music component such as a bass or a drum is known. For example, Patent Document 1 discloses a first detection unit that detects a level of 100 Hz or less where a bass or drum music component exists, and a second detection unit that detects a level of 100 Hz or more where a vocal or lead guitar music component exists. And a control means for adjusting a frequency characteristic of 100 Hz or less in accordance with a ratio of detection levels detected by the first detection means and the second detection means is disclosed. With this configuration, when the bass and drum music components whose frequency characteristics you want to adjust are relatively large, the low frequency boost amount increases, and when the vocal and lead guitar music components you do not want to adjust the frequency characteristics are relatively large Since the amount of boost in the low range is reduced, the problem of emphasizing vocals and lead guitars at the same time as the bass and drums has been resolved against the will of the user.

Japanese Patent Laid-Open No. 11-17480

  By the way, in general, when a bass sound such as a bass drum (kick) is to be emphasized, a method of amplifying and emphasizing a low frequency component of 100 Hz or less is employed as in the above-described frequency characteristic adjusting device. However, the bass drum attack period (a period of several tens of msec starting from the moment when the mallet hits the striking surface) contains high frequency components in the middle and high ranges. For this reason, when only the low frequency range of 100 Hz or less is amplified in order to emphasize the bass drum sound as in the frequency characteristic adjusting device described above, the power of the low sound is produced, but the attack sound is felt relatively small, and the attack sound is reduced. The sound is unclear and unclear. In order to solve this, it is conceivable to amplify the mid-high range music component, but generally the mid-high range contains the music component of other instruments. The instrument sound is also emphasized, and the effect of enhancing the attack sound is diminished. In other words, with the conventional technology, it is difficult to emphasize a musical instrument sound having a relatively wide band of musicality, such as a bass drum sound, in a balanced manner without affecting other musical instrument sounds. .

  In view of the above problems, the present invention provides an audio signal processing device, a control method for an audio signal processing device, and a program capable of enhancing a specific instrument sound in a balanced manner without affecting other instrument sounds. The purpose is to provide.

  An audio signal processing device of the present invention is detected by an extraction unit that extracts a first frequency band component of an input audio signal, an attack period detection unit that detects an attack period of the extracted audio signal, and an attack period detection unit And an amplifying unit that amplifies the second frequency band component of the input audio signal (where the first frequency band component is not equal to the second frequency band component) during the attack period. .

  An audio signal processing apparatus control method according to the present invention includes an extraction step of extracting a first frequency band component of an input audio signal, an attack period detection step of detecting an attack period of the extracted audio signal, and an attack period detection Performing an amplification step of amplifying the second frequency band component of the input audio signal (where the first frequency band component is not equal to the second frequency band component) during the attack period detected in the step. Features.

  In the above audio signal processing device, the first frequency band component is a low frequency band component, and the second frequency band component is a medium high frequency band component.

According to the configuration of the present invention, the attack period of the first frequency band component of the input audio signal is detected, and the second frequency band component different from the first frequency band component is amplified in the attack period. So, for example, when you want to emphasize bass drum sound, you can enhance bass drum attack sound without affecting other instrument sounds by amplifying middle and high frequency band components during the attack period of low frequency band components Can do. In addition to amplifying the second frequency band component (mid-high frequency band component) and amplifying the first frequency band component (low frequency band component) (for example, by performing amplification using an equalizer or the like), a bass drum The sound can be emphasized in a balanced manner.
The first frequency band component and the second frequency band component may be at least partially different from each other. In other words, part of the first frequency band component and the second frequency band component may overlap.
Further, the present invention can be applied not only to bass drums but also to processing that emphasizes the attack sound of other percussion instruments or instruments other than percussion instruments. Here, the “attack sound” refers to a sudden and shocking sound at the beginning of the instrument. In addition, the “attack period” refers to a period from when the instrument sound starts to sound until a specific frequency band component falls to a certain value.
The attack period may be detected by detecting only the attack time point (start point of the attack period) of the first frequency band component and defining a certain period from the attack time point as the attack period.

  In the audio signal processing device, the attack period detection unit has an output value obtained by passing the extracted audio signal through the first bandpass filter having the first time constant, and a second time constant larger than the first time constant. The attack period is detected based on the output value passed through the second band pass filter.

According to the configuration of the present invention, for example, the amplitude envelope is compared with a threshold value, a minimum value is searched from the time when the threshold value is exceeded, and compared with a known method in which the position is set as the attack time point. It can be detected accurately. That is, in the known method, since it is compared with an absolute threshold value, if the signal level of the audio signal does not exceed the value, the attack period cannot be detected. Since the attack period is detected using a type of bandpass filter, the attack period can be reliably detected without being affected by the signal level.
When detecting the bass drum attack period, it is preferable to use a low-pass filter as the band-pass filter.

  In the above audio signal processing device, the attack period detection unit detects a period in which a value obtained by subtracting the output value of the second bandpass filter from the output value of the first bandpass filter is 0 or more as the attack period. Features.

  According to the configuration of the present invention, it is possible to detect the attack period easily and accurately by using the difference in the rise and fall timings of the amplitude envelope obtained from the output values of the two types of bandpass filters.

  In the audio signal processing device, the amplification unit amplifies the second frequency band component according to the signal level of the extracted audio signal.

  According to the configuration of the present invention, for example, when it is desired to emphasize the bass drum sound, the enhancement degree is high in the portion where the bass drum sound is high, and the enhancement degree is lowered in the portion where the bass drum sound is low. It is possible to prevent the sound from being emphasized.

  A program according to the present invention causes a computer to execute each step in the above-described method for controlling an audio signal processing device.

  By using this program, it is possible to realize a control method of an audio signal processing apparatus that can emphasize a specific instrument sound in a balanced manner without affecting other instrument sounds.

It is a block diagram of the reproduction | regeneration system which concerns on one Embodiment of this invention. It is a block diagram of an audio | voice signal processing part. It is a figure which shows the relationship between the audio | voice signal waveform of a bass drum, and the attack period of a bass drum. It is the figure which expanded a part of FIG. 3 in the time direction. It is a circuit block diagram of an attack emphasis processing part. FIG. 4 is a diagram in which output waveforms of the first LPF and the second LPF are superimposed on FIG.

  Hereinafter, an audio signal processing device, a control method for the audio signal processing device, and a program according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a reproduction system SY according to an embodiment of the present invention. The reproduction system SY includes a sound source 1, an audio signal processing unit 2, a power amplifier 3, and a speaker 4. In the figure, for simplification, two channels of LR (left signal and right signal) are indicated by one line. The “audio signal processing device” in the claims corresponds to the audio signal processing unit 2.

  The sound source 1 supplies an audio signal to the audio signal processing unit 2, and includes various storage media (CD, SD card, USB memory, etc.), various electronic devices (audio player, personal computer, tablet terminal, mobile phone). Etc.) and various servers (servers on the Web, servers on the LAN network, etc.).

  The audio signal processing unit 2 performs various audio processes on the audio signal supplied from the sound source 1. In particular, in the present embodiment, by performing bass drum sound enhancement processing, a music reproduction with a beat is realized. Further, when emphasizing the bass drum sound, audio processing is performed by dividing it into a low frequency band component (first frequency band component) and a medium high frequency band component (second frequency band component). Details will be described later.

  The power amplifier 3 amplifies the audio signal processed by the audio signal processing unit 2 and drives the speaker 4. The speaker 4 outputs an audio signal by driving the power amplifier 3. The power amplifier 3 may be built in the speaker 4. The audio signal processing unit 2 may be realized by software such as a DSP (Digital Signal Processor) or an analog device. Further, headphones or earphones may be used instead of the speakers 4.

  In addition, the playback system SY of this embodiment is suitable for DJ equipment such as a DJ speaker, DJ mixer, DJ player, etc., where bass drum sound is highly emphasized, but also for other playback systems (minicomponents, headphone amplifiers, etc.). Applicable.

  Next, the configuration of the audio signal processing unit 2 will be described with reference to FIG. The audio signal processing unit 2 includes a low frequency emphasis processing unit 10 and an attack emphasis processing unit 20. Also in the figure, the two LR channels are indicated by a single line.

  The low frequency emphasis processing unit 10 emphasizes the low frequency band component of the bass drum sound by a known method such as an emphasis process using an equalizer. On the other hand, the attack emphasis processing unit 20 emphasizes medium and high frequency band components (middle and high frequency band components) during an attack period in which a bass drum attack sound is generated. That is, the middle and high frequency band components are emphasized only in the attack period, and the low frequency band components are emphasized regardless of the attack period. Thereby, the bass drum sound can be emphasized in a well-balanced manner without affecting other instrument sounds.

  Here, the “attack sound” refers to the sound at the moment when the bass drum mallet hits the striking surface. The “attack period” refers to a period from the beginning of the bass drum sound until the middle and high frequency band components of the bass drum sound fall to a certain value.

  FIG. 3 is a diagram showing the relationship between the bass drum sound signal waveform and the bass drum attack period. FIG. 4 is an enlarged view of a part of FIG. 3 in the time direction. In both figures, the horizontal axis indicates time, and the vertical axis indicates the amplitude (gain) of the audio signal. A symbol L0 (shown in bold solid line) superimposed on the audio signal waveform indicates the bass drum attack period, that is, the timing at which the bass drum attack sound is emphasized. The waveform of the code L0 is generated by analyzing the low frequency band component in the attack emphasis processing unit 20 (bass drum sound detection unit 22, see FIG. 5), and variable amplifiers 43a and 43b (intermediate / high range addition) to be described later. Used as a gain of the embedding unit 24 (see FIG. 5). As described above, the attack enhancement processing unit 20 detects the attack period of the bass drum sound from the low frequency band components, and emphasizes the middle and high frequency band components for each attack period.

  FIG. 5 is a circuit configuration diagram of the attack enhancement processing unit 20. As shown in the figure, the attack enhancement processing unit 20 includes an LR adder 21, a bass drum sound detection unit 22, a delay unit 23, and a mid-high range addition unit 24.

  The LR adder 21 adds the L signal and the R signal and outputs a monaural signal. The bass drum sound detection unit 22 analyzes a low frequency band component of the audio signal input to the audio signal processing unit 2 and detects an attack period (generates a waveform with a code L0). Further, the middle / high frequency band adding unit 24 emphasizes the middle / high frequency band component in the attack period detected by the bass drum sound detection unit 22. The delay unit 23 also corrects the processing delay of the bass drum sound detection unit 22 with respect to the processing of the mid-high range adding unit 24.

  Here, the bass drum sound detection unit 22 will be described in detail. The bass drum sound detection unit 22 includes a third LPF (low-pass filter) 31 for detecting bass drum sound, an ABS 32, a first LPF 33 (first band-pass filter) with a time constant of 1, and a second LPF 34 (second band-pass filter with a time constant of 2). ), A subtractor 35, a first limiter 36, a variable amplifier 37, and a second limiter 38.

  In the bass drum sound detection unit 22, first, the audio signal output from the LR adder 21 is limited to a bass drum band (for example, 100 Hz or less) by the third LPF 31. Then, after calculating the absolute value by the ABS 32, two types of output waveforms are obtained by applying two types of LPFs 33 and 34 having different time constants. FIG. 6 is a diagram in which these two types of output waveforms (amplitude envelopes) are superimposed on FIG. In FIG. 6, a symbol L <b> 1 (illustrated, thin dotted line) indicates an output waveform of the first LPF 33, and a symbol L <b> 2 (illustrated, thin solid line) indicates an output waveform of the second LPF 34.

  In addition, the time constant 1 of the first LPF 33 is required to be smaller than the time constant 2 of the second LPF 34. In this case, as shown in FIG. 6, the output of the first LPF 33 having a smaller time constant than the output waveform (reference numeral L2) of the second LPF 34 having a large time constant at a steep rising portion such as the moment when the bass drum sounds. The waveform (symbol L1) rises earlier. Thereafter, as the reverberation of the bass drum sound becomes smaller, all output waveforms turn downward. At this falling portion, the time constant is larger than the output waveform (reference L2) of the second LPF 34 having a large time constant. The output waveform (symbol L1) of the first LPF 33 having a smaller value becomes smaller earlier. Thus, due to the difference in time constant, a period occurs in which the output waveform (reference L1) of the first LPF 33 is larger than the output waveform (reference L2) of the second LPF 34. The subtracter 35 at the subsequent stage detects these differences. That is, the period in which the output value of the first LPF 33 is equal to or greater than the output value of the second LPF 34 (the time when the output value of the first LPF 33 is equal to or greater than the output value of the second LPF 34 is set as the start point, and then the output value of the first LPF 33 is less than the output value of the second LPF 34 Is detected as an attack period. The subtractor 35 performs subtraction in decibel conversion.

  Further, as shown in FIG. 5, the first limiter 36 at the subsequent stage limits to 0 when the output value x1 of the subtractor 35 becomes a negative value. Further, the variable amplifier 37 at the subsequent stage amplifies the output value of the first limiter 36 according to the signal level of the low frequency band component. Here, the output value of the first LPF 33 is used as the signal level. That is, the variable amplifier 37 controls the amplification amount of a signal indicating the difference between the first LPF 33 and the second LPF 34 at the output level of the first LPF 33. As a result, the higher the bass drum sound is, the greater the amount of enhancement in the attack period is.

  For example, when the bass drum is not sounding and there is a level fluctuation of the bass guitar having the same low frequency band component as the bass drum, it is not desired to add the middle and high frequency band components. Since the amplitude of the bass guitar waveform is generally smaller than that of the bass drum, it is suppressed by the variable amplifier 37, and the middle and high frequency band components are hardly emphasized. That is, it is emphasized only when a loud sound such as a bass drum is input, and as a result, the operation is performed such that the bass drum is selected and amplified. As a result, it is possible to eliminate the adverse effect of adding the middle and high frequency band components at unnecessary timing by the middle and high frequency band adding unit 24 described later. Thereafter, the second limiter 38 at the subsequent stage limits the maximum value of the output value x2 of the variable amplifier 37 to a predetermined value β. This is to suppress variations in the effects of music.

  Next, the mid-high range adding portion 24 will be described. The mid-high range adder 24 includes two LPFs 41 (fourth LPF 41a and fifth LPF 41b) having the same time constant, two HPFs (high pass filters) 42 (first HPF 42a and second HPF 42b) having the same time constant, and two variable amplifiers 43 (variable). An amplifier 43a and a variable amplifier 43b) and two adders 45 (an adder 45a and an adder 45b) are provided.

  The fourth LPF 41a and the first HPF 42a extract the middle and high frequency band components of the L signal. Similarly, the fifth LPF 41b and the second HPF 42b extract the middle and high frequency band components of the R signal. The variable amplifier 43a and the variable amplifier 43b amplify the middle and high frequency band components of the extracted L signal and R signal, respectively. These variable amplifiers 43 a and 43 b control the amount of amplification based on the output level of the bass drum sound detector 22. That is, based on the waveform of the code L0 shown in FIGS. 4 and 6, the middle and high frequency band components of the input audio signal are amplified only during the attack period in which the value is not 0 and is a mountain shape. Thereby, the emphasis synchronized with the attack sound of the bass drum can be performed.

  Then, the adder 45a and the adder 45b in the subsequent stage add the medium and high frequency band components of the amplified L signal and R signal to the original signal (L signal and R signal), respectively. The original signal is delay-adjusted by the delay unit 23. In other words, the delay unit 23 should correct that the attack period detected by the bass drum sound detection unit 22 is slightly later than the period in which the mid-high frequency band component of the bass drum sound to be actually emphasized exists. Then, delay processing is performed on the original signal. 4 and 6 are shifted to the left side by this delay in accordance with the emphasis timing on the actual time axis. The adders 45a and 45b add the amplified medium and high frequency band components to the original signal after the delay processing.

  The “extraction unit” in the claims mainly includes the third LPF 31 of the bass drum sound detection unit 22. The “attack period detection unit” in the claims mainly includes the first LPF 33, the second LPF 34, and the subtractor 35 of the bass drum sound detection unit 22. Further, the “amplifying unit” in the claims mainly includes the variable amplifier 37 and the second limiter 38 of the bass drum sound detecting unit 22 and the variable amplifiers 43 a and 43 b of the mid-high range adding unit 24.

  As described above, the attack emphasis processing unit 20 of the present embodiment amplifies the middle and high frequency band components with respect to the attack period detected from the analysis result of the low frequency band components of the input audio signal, and therefore only the attack period. The medium and high frequency band components can be amplified. That is, as a part of the bass drum sound enhancement processing, the mid-high frequency band component is amplified for each bass drum attack, so that the attack sound can be enhanced without affecting other instrument sounds. Further, since the low frequency band component enhancement processing by the low frequency enhancement processing unit 10 is performed together with the processing by the attack enhancement processing unit 20, the bass drum sound can be emphasized with a good balance.

  In addition, since the attack enhancement processing unit 20 detects the attack period using two types of LPFs 33 and 34 having different time constants, it detects an accurate attack period without being affected by the signal level of the input audio signal. can do. In addition, since the amplification of the medium and high frequency band components changes the gain according to the signal level of the low frequency band components, it is possible to prevent the adverse effect of adding the medium and high frequency band components at unnecessary timing. Thus, the attack period of the bass drum can be more effectively enhanced by detecting the attack period regardless of the signal level, and varying the amount of amplification of the middle and high frequency band components according to the signal level. Also, neither the detection of the attack period nor the control of the amount of amplification of the mid-high frequency band component requires analysis of the mid-high frequency band component (detects the attack period from the audio signal of the mid-high frequency band component, Another feature of the present embodiment is that the amount of amplification is not controlled in accordance with the signal level.

  In addition, the following modifications can be employed. For example, in the above embodiment, the case where the bass drum sound is emphasized is illustrated, but the present invention can be applied to a process of enhancing other percussion instrument sounds or instrument sounds other than percussion instruments. In this case, the band for detecting the attack period (first frequency band component) is not limited to the low frequency band component. Further, the band to be amplified (second frequency band component) is not limited to the medium / high frequency band component. In other words, depending on the musical instrument sound, processing such as detecting the attack period from the analysis result of the medium and high frequency band components and amplifying the low frequency band component only during the attack period can be considered. However, depending on the musical instrument sound such as bass drum sound, the band for detecting the attack period and the band to be amplified do not overlap (the first frequency band component and the second frequency band component are separated). To be set).

  As a further modification, depending on the musical instrument sound, the first frequency band component and the second frequency band component may be set to overlap each other. In addition, the user may be able to set and change the band of the first frequency band component and the second frequency band component for each instrument sound to be emphasized.

  In the above embodiment, the bass drum sound detector 22 detects the start point and end point of the attack period. However, only the attack time point (start point of the attack period) may be detected. In this case, a certain period from the detected attack time may be defined as the attack period.

  In the above embodiment, the L signal and the R signal are added by the LR adder 21 and detected by the bass drum sound detection unit 22. However, the LR signal is individually processed to detect the attack period. May be. In this case, the mid-high frequency band adding unit 24 adds the mid-high frequency band components of the corresponding channel.

  In the above-described embodiment, the method of adding gain to the original signal (original signal) by controlling the gain of the medium / high frequency band components extracted by the LPF 41 and the HPF 42 in the medium / high frequency band adding unit 24 is described. A method of controlling the gain of the frequency band component may be used.

  In the above embodiment, the attack emphasis processing unit 20 includes the delay unit 23. However, the delay unit 23 may be omitted. In this case, it is preferable to adjust the time constants of the first LPF 33 and the second LPF 34 so as to reduce the delay amount.

  In the above embodiment, as shown in FIG. 2, the low frequency emphasis process and the attack emphasis process are performed separately, but the emphasis process may be performed in the same processing circuit. For example, low-frequency emphasis processing may be performed between the delay unit 23 and the mid-high frequency adding unit 24 of the attack emphasis processing unit 20 (see FIG. 5).

  Further, it is possible to provide each component and each processing step of the reproduction system SY (particularly, the audio signal processing unit 2) shown in the above embodiment and the modified example as a program. Further, the program can be provided by being stored in various storage media (CD-ROM, flash memory, etc.). That is, a program for realizing each component or each processing step of the reproduction system SY and a storage medium storing the program are also included in the scope of the right of the present invention.

  In the above-described embodiment and modification, the case where the audio signal processing unit 2 (“audio signal processing device” in the claims) is applied to the reproduction system SY is illustrated. The present invention may be applied to other electronic devices such as a tablet terminal, a mobile phone, or a car navigation device. Further, the audio signal processing unit 2 may be applied to cloud computing, such as realized by a server on the Web or a server on a LAN network. Other modifications can be made as appropriate without departing from the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Sound source 2 ... Audio | voice signal processing part 3 ... Power amplifier 4 ... Speaker 10 ... Low frequency emphasis processing part 20 ... Attack emphasis processing part 21 ... LR adder 22 ... Bass drum sound detection part 23 ... Delay part 24 ... Middle high frequency addition Insertion unit 31 ... third LPF 32 ... ABS 33 ... first LPF 34 ... second LPF 35 ... subtractor 36 ... first limiter 37 ... variable amplifier 38 ... second limiter 41a ... fourth LPF 41b ... fifth LPF 42a ... first HPF 42b ... first 2HPF 43 ... Variable amplifier 45 ... Adder SY ... Reproduction system

Claims (7)

An extractor for extracting a first frequency band component of the input audio signal;
An attack period detector for detecting an attack period of the extracted audio signal;
An amplifying unit for amplifying a second frequency band component of the input audio signal (where first frequency band component ≠ second frequency band component) in the attack period detected by the attack period detecting unit; An audio signal processing device comprising:   The audio signal processing apparatus according to claim 1, wherein the first frequency band component is a low frequency band component, and the second frequency band component is a medium-high frequency band component. The attack period detector is
An output value obtained by passing the extracted audio signal through a first band pass filter having a first time constant; an output value obtained by passing a second band pass filter having a second time constant greater than the first time constant; The audio signal processing apparatus according to claim 1, wherein the attack period is detected based on the voice signal. The attack period detector is
4. The audio signal according to claim 3, wherein a period in which a value obtained by subtracting an output value of the second bandpass filter from an output value of the first bandpass filter is 0 or more is detected as the attack period. 5. Processing equipment. The amplification unit is
5. The audio signal processing apparatus according to claim 1, wherein the second frequency band component is amplified in accordance with a signal level of the extracted audio signal. 6. An extraction step of extracting a first frequency band component of the input audio signal;
An attack period detecting step of detecting an attack period of the extracted audio signal;
An amplifying step for amplifying a second frequency band component of the input audio signal (wherein the first frequency band component is not equal to the second frequency band component) in the attack period detected in the attack period detecting step; A control method for an audio signal processing device, characterized in that   The program for making a computer perform each step in the control method of the audio | voice signal processing apparatus of Claim 6.

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