Bass enhancement method and bass enhancement device

Abstract

To generate a signal with emphasized low frequency while occurrence of distortion of sound and continuous sound generated by a harmonic instrument is suppressed.SOLUTION: A bass enhancement device 20 includes: an extraction part 21; a generation part 22; and a synthesis part 24. The extraction part 21 extracts a percussion signal b2 indicating a percussion sound component from an input sound signal a1 including a harmonic instrument sound component and a percussion sound component. The generation part 22 generates a low frequency signal c4 based on the percussion signal b2. The low frequency signal c4 is a signal having a frequency which is 1 / 2 of a frequency of a fundamental wave component of the percussion signal b2. The synthesis part 24 generates a low frequency emphasis signal e1 based on the low frequency signal c4 and the input sound signal a1. The low frequency emphasis signal e1 is a signal whose low frequency component of the input sound signal a1 is emphasized.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a bass enhancement method and device. [Background technology]

[0002] In an audio system, a device that emphasizes the low frequency range of an input sound signal and reproduces it is known. For example, Patent Document 1 discloses a bass-emphasizing reproduction device that extracts low frequency components from an input signal using a low-pass filter, generates ultra-low frequency components with a frequency half that of the extracted low frequency components, adds the ultra-low frequency components and the low frequency components, and further adds the sum of the ultra-low frequency components and the low frequency components to the input signal, thereby obtaining an output signal with emphasized low frequencies. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-67628 A Summary of the Invention [Problem to be solved by the invention]

[0004] The bass emphasis reproduction device described in Patent Document 1 has a problem in that when an ultra-low frequency component is added to the original sound, sounds generated by harmonic instruments and sustained sounds are perceived as being significantly distorted.

[0005] In consideration of the above circumstances, one aspect of the present disclosure aims to provide a bass enhancement method that generates a signal with enhanced low frequencies while suppressing distortion of sounds generated by harmonic instruments and sustained sounds. [Means for solving the problem]

[0006] In order to solve the above problems, a bass emphasis method according to one embodiment of the present disclosure includes: extracting a non-harmonic instrument signal indicative of a non-harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components; generating a low-frequency signal having a frequency that is 1 / N (N is an integer equal to or greater than 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal; and generating a bass emphasis signal in which the low-frequency component of the input sound signal is emphasized based on the low-frequency signal and the input sound signal.

[0007] A bass emphasis device according to one aspect of the present disclosure includes an extraction unit that extracts a non-harmonic instrument signal indicative of a non-harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components; a first generation unit that generates a low-frequency signal having a frequency that is 1 / N (N is an integer greater than or equal to 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal; and a second generation unit that generates a bass emphasis signal in which the low-frequency components of the input sound signal are emphasized based on the low-frequency signal and the input sound signal.

[0008] A bass enhancement device according to one embodiment of the present disclosure includes an extraction unit that extracts a non-harmonic instrument signal indicative of a harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components; a generation unit that generates a low-frequency signal having a frequency that is 1 / N (N is an integer greater than or equal to 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal; and an output unit that outputs an output sound signal including at least the low-frequency signal to an actuator that vibrates a seat. [Brief description of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing an example of an audio system including a bass enhancement device according to a first embodiment. [Diagram 2] 2 is a block diagram showing the functions of an extraction unit in FIG. 1; [Diagram 3]FIG. 2 illustrates an example of a spectrogram with harmonic instrument sound components. [Figure 4] FIG. 2 is a diagram showing an example of a spectrogram having percussion sound components. [Diagram 5] FIG. 2 is a block diagram showing the functions of a generation unit in FIG. 1. [Figure 6] FIG. 11 is a diagram illustrating an example of a second bass signal. [Figure 7] FIG. 13 is a diagram for explaining waveform folding; [Figure 8] FIG. 4 illustrates an example of a low-frequency percussion signal. [Figure 9] FIG. 13 is a diagram illustrating an example of a third bass signal. [Figure 10] FIG. 11 is a configuration diagram showing an example of an audio system including a bass enhancement device according to a first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A: First embodiment A1: Configuration of bass booster

[0011] 1 is a configuration diagram showing an example of an audio system 1 including a bass enhancement device 20 according to a first embodiment. The audio system 1 is mounted on a vehicle such as an automobile. As shown in FIG. 1, the audio system 1 includes a storage device 10, a bass enhancement device 20, an amplifier device 30, and a speaker device 40.

[0012] In the acoustic system 1, the bass emphasis device 20 generates a bass emphasis signal e1 based on an input sound signal a1 input from a sound source 2, and the amplifier device 30 amplifies the generated bass emphasis signal e1 and outputs it as an amplified sound signal e2 to the speaker device 40. The speaker device 40 emits sound based on the amplified sound signal e2.

[0013] The storage device 10 is a recording medium readable by a computer (e.g., a non-transitive recording medium readable by a computer). The storage device 10 includes a non-volatile memory and a volatile memory. The non-volatile memory is, for example, a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM), and an Electrically Erasable Programmable Read Only Memory (EEPROM). The volatile memory is, for example, a Random Access Memory (RAM).

[0014] The storage device 10 stores a program p1 and various information. The program p1 defines the operation of the bass enhancement device 20. The storage device 10 may store the program p1 read from a storage device in a server (not shown). In this case, the storage device in the server is an example of a computer-readable recording medium.

[0015] The bass emphasis device 20 reads the program p1 from the storage device 10. By executing the program p1, the bass emphasis device 20 functions as an extraction unit 21, a generation unit 22, a delay unit 23, and a synthesis unit 24. At least one of the extraction unit 21, the generation unit 22, the delay unit 23, and the synthesis unit 24 may be realized by a circuit such as a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA).

[0016] The input sound signal a1 is input to the extraction unit 21 from the sound source 2. The input sound signal a1 includes harmonic instrument sound components and non-harmonic instrument sound components. The harmonic instrument sound components are components that can be decomposed into a fundamental frequency component and a component of a frequency that is an integer multiple of the fundamental frequency. For example, sounds from string instruments, wind instruments, vocal sounds, etc. include harmonic instrument sound components. The harmonic instrument sound components are elements that determine the pitch and timbre of a sound, and are sustained sounds. In contrast, the non-harmonic instrument sound components are components other than the harmonic instrument sound components. The non-harmonic instrument sound components have random frequency components compared to the harmonic instrument sound components, and are non-sustained sounds. The non-harmonic instrument sound components include percussion instrument sound components. The percussion instrument sound components are components of sounds mainly generated from percussion instruments. In reality, most non-harmonic instrument sounds are percussion instrument sound components, and it can be said that the percussion instrument sound components are substantially equivalent to the non-harmonic instrument sound components. For example, drum sounds and cymbal sounds have percussion sound components. Even sounds produced by harmonic instruments may contain percussion sound components depending on the playing style. Percussion sound components are elements that determine the rhythm and dynamics of the sound.

[0017] The extraction unit 21 separates the input sound signal a1 into a harmonic instrument sound component and a percussion instrument sound component, and extracts a signal representing the separated percussion instrument sound component as a percussion instrument signal b2. The percussion instrument sound component is an example of a "non-harmonic instrument sound component," and the percussion instrument signal b2 is an example of a "non-harmonic instrument signal."

[0018] The generating unit 22 generates a low-frequency signal c4 based on the percussion signal b2. The low-frequency signal c4 has a frequency half the frequency of the fundamental component of the percussion signal b2. The generating unit 22 is an example of a "first generating unit."

[0019] The delay unit 23 generates a delayed sound signal d1 based on the input sound signal a1. The delayed sound signal d1 is a signal obtained by delaying the input sound signal a1 by the time required to generate the low-frequency signal c4.

[0020] The synthesis unit 24 generates a low-frequency emphasis signal e1 by synthesizing the low-frequency signal c4 and the delayed sound signal d1. The low-frequency emphasis signal e1 is a signal in which the low frequency components of the delayed sound signal d1 are emphasized. In other words, the synthesis unit 24 generates the low-frequency emphasis signal e1 based on the low-frequency signal c4 and the input sound signal a1. The combination of the delay unit 23 and the synthesis unit 24 is an example of a "second generation unit."

[0021] The extraction unit 21 will be described in more detail below with reference to Fig. 2 to Fig. 4. Fig. 2 is a block diagram showing the functions of the extraction unit 21 in Fig. 1. As shown in Fig. 2, the extraction unit 21 has a low-pass filter 211 and a percussion sound extraction unit 212.

[0022] The low-pass filter 211 is a second-order infinite impulse response filter (IIR filter). The cutoff frequency of the low-pass filter 211 is 200 Hz. The low-pass filter 211 generates a first bass signal b1 by attenuating frequency components of the input sound signal a1 that have a frequency higher than 200 Hz.

[0023] The cutoff frequency of low-pass filter 211 is not limited to 200 Hz. For example, the cutoff frequency of low-pass filter 211 may be 200 Hz plus or minus K% (e.g., 20%). Furthermore, low-pass filter 211 is not limited to a second-order IIR filter. For example, low-pass filter 211 may be a first-order IIR filter or a third-order IIR filter, or may be a digital filter other than an IIR filter, such as an FIR filter (Finite Impulse Response Filter).

[0024] The percussion sound extraction unit 212 separates the first bass signal b1 into a harmonic instrument sound component and a percussion sound component to extract a percussion signal b2. The percussion sound extraction unit 212 uses, for example, a known method of HPSS (Harmonic-Percussive Source Separation) as a method for separating the harmonic instrument sound component and the percussion sound component.

[0025] HPSS is a technique for filtering sound signals by decomposing the sound signal in the time-frequency domain using a short-time Fourier transform and utilizing the difference between the characteristics of harmonic instrument sound components and percussion sound components. The short-time Fourier transform cuts out the sound signal using a window function of a certain size, and then performs a Fourier transform on the cut-out signal to calculate the spectrum. The time-frequency domain is a plane whose vertical axis represents frequency and whose horizontal axis represents time. A graph showing the intensity of a sound signal that has been subjected to a short-time Fourier transform in the time-frequency domain is called a spectrogram. The vertical axis of the spectrogram represents frequency, and the horizontal axis of the spectrogram represents time. Therefore, the vertical axis is also called the frequency axis, and the horizontal axis is also called the time axis.

[0026] Fig. 3 is a diagram showing an example of a spectrogram having a harmonic instrument sound component, and Fig. 4 is a diagram showing an example of a spectrogram having a percussion instrument sound component.

[0027] Harmonic instrumental sound components are sustained sounds whose pitch is easily recognized. As shown in Fig. 3, when viewed in the time-frequency domain, harmonic instrumental sound components have the characteristics of being steep along the frequency axis and smooth along the time axis.

[0028] On the other hand, percussion sound components are non-sustained sounds whose pitch is difficult to recognize. As shown in Figure 4, when viewed in the time-frequency domain, percussion sound components have the characteristic of being smooth along the frequency axis and steep along the time axis.

[0029] In this way, by utilizing the anisotropy of smoothness on the spectrogram between the harmonic instrument sound components and the percussion instrument sound components, the harmonic instrument sound components and the percussion instrument sound components can be separated by applying a filter to the spectrogram.

[0030] A filter for extracting harmonic instrument sound components may be, for example, a vertically long rectangular filter. Harmonic instrument sound components are extracted by averaging along the vertical axis of the spectrogram using a vertically long rectangular filter. Furthermore, the influence of percussion sound components can be removed by averaging along the time axis within the range of the filter.

[0031] The filter for extracting the percussion sound components is, for example, a horizontally long rectangular filter. The percussion sound components are extracted by averaging along the horizontal axis of the spectrogram using the horizontally long rectangular filter. Furthermore, the influence of harmonic instrument sound components can be removed by averaging along the frequency axis within the range of the filter.

[0032] More specifically, the percussion sound extraction unit 212 performs a short-time Fourier transform on the first bass signal b1 and outputs the result of the short-time Fourier transform as a spectrogram. The percussion sound extraction unit 212 extracts percussion sound components by filtering the output spectrogram. The percussion sound extraction unit 212 then converts the extracted percussion sound components into a time-domain sound signal by an inverse short-time Fourier transform and outputs the signal as a percussion signal b2.

[0033] Next, the generation unit 22 will be described in detail with reference to Fig. 5 to Fig. 9. Fig. 5 is a block diagram showing the functions of the generation unit 22 in Fig. 1. As shown in Fig. 5, the generation unit 22 has a low-pass filter 221, a low-frequency generation unit 222, a low-pass filter 223, and a gain controller 224.

[0034] The low-pass filter 221 extracts low-frequency components from the percussion signal b2 and outputs them as a second bass signal c1. The cutoff frequency of the low-pass filter 221 is 200 Hz. Therefore, the low-pass filter 221 extracts low-frequency components below 200 Hz from the percussion signal b2. The cutoff frequency of the low-pass filter 221 does not have to be 200 Hz. For example, the cutoff frequency of the low-pass filter 221 may be a frequency within the range of 200 Hz plus or minus K% (e.g., 20%).

[0035] The bass generating unit 222 generates a signal having a frequency component that is half the frequency of the fundamental wave component of the percussion signal b2, based on the second bass signal c1 output by the low-pass filter 221. The generated signal is one octave lower than the second bass signal c1, and is therefore called a bass percussion signal c2.

[0036] Known methods for generating the low-frequency percussion signal c2 include a method for generating the signal in the time domain and a method for generating the signal in the frequency domain. Methods for generating the low-frequency percussion signal c2 in the time domain include a general zero-crossing detection method and a method for generating a waveform with a double period by folding back the waveform at the zero-crossing point.

[0037] The zero-cross detection method utilizes the fact that the output state of a comparator changes when the signal waveform crosses the zero reference voltage. Zero-cross detection produces a square wave with a period equal to that of the signal waveform. Then, by dividing the resulting square wave in half, a low-frequency component with half the frequency is obtained.

[0038] In addition, a method for generating the low-frequency percussion signal c2 in the frequency domain includes converting a time domain signal into a frequency domain signal using an FFT (Fast Fourier Transform), detecting the pitch in the frequency domain, and generating a signal with a frequency that is half the frequency of the detected pitch using a VCO (Voltage Controlled Oscillator).

[0039] In this embodiment, a method of folding back the waveform at the zero crossing point is adopted. Hereinafter, a method of generating the low-frequency percussion signal c2 by the low-frequency generating unit 222 will be described with reference to Figs. 6 to 8. Fig. 6 is a diagram showing an example of the second low-frequency signal c1. Fig. 7 is a diagram for explaining the folding back of the waveform. Fig. 8 is a diagram showing an example of the low-frequency percussion signal c2.

[0040] An example will be described in which the second bass signal c1 input to the bass generating unit 222 has a sine waveform as shown in Fig. 6. In this case, the bass generating unit 222 takes two periods of the sine waveform, i.e., a phase range TR of 720°, as a repeating unit, as shown in Fig. 7, and folds the sine waveform back at the zero level line every 360° phase in the phase range TR. More specifically, of the two sections T1 and T2 of the phase range TR, the bass generating unit 222 does not fold back the sine waveform in section T1, but folds back the sine waveform in section T2.

[0041] Therefore, the process shown in Fig. 7 changes the waveform as shown in Fig. 8. The period of the waveform shown in Fig. 8 is twice as long as that of the original percussion signal b2. In this way, a low-frequency percussion signal c2 with twice the period, i.e., one octave lower, is generated from the second bass signal c1 extracted by the low-pass filter 221.

[0042] FIG. 9 is a diagram showing an example of the third bass signal c3. As shown in FIG. 9, the low-pass filter 223 removes unnecessary harmonics contained in the low-frequency percussion signal c2. The cut-off frequency of the low-pass filter 223 is 100 Hz. As a result, the third bass signal c3 from which unnecessary harmonics have been removed is output from the low-pass filter 223. Note that the cut-off frequency of the low-pass filter 223 is not limited to 100 Hz. For example, the cut-off frequency of the low-pass filter 223 may be 100 Hz plus or minus K% (e.g., 20%).

[0043] The gain controller 224 adjusts the gain of the third bass signal c3 output from the low-pass filter 223. The gain controller 224 outputs the gain-adjusted third bass signal c3 as a low-frequency signal c4 to the synthesis unit 24. The gain of the gain controller 224 can be appropriately set by a user who sets up the acoustic system 1.

[0044] The delay unit 23 delays the input sound signal a1. The delay unit 23 generates the delayed input sound signal a1 as a delayed sound signal d1 and outputs it to the synthesis unit 24. The delay time by the delay unit 23 is set in advance to be equal to the sum of the delay time generated in the extraction unit 21 and the delay time generated in the generation unit 22. In other words, the delay time by the delay unit 23 is the time it takes to generate the low-frequency signal c4 based on the input sound signal a1.

[0045] In addition, the low-frequency signal rises slower than the mid-frequency or high-frequency signals. Therefore, the delay time may be set so that the timing of the low-frequency signal c4 relative to the delayed sound signal d1 is advanced. In other words, the delay time by the delay unit 23 may be set so as to be longer than the time required to generate the low-frequency signal c4 based on the input sound signal a1. This further emphasizes the feeling of low-frequency sound. In addition, the delay unit 23 may have a function of a gain controller.

[0046] The synthesis unit 24 generates a low-frequency emphasis signal e1 based on the low-frequency signal c4 and the delayed sound signal d1. More specifically, the synthesis unit 24 generates the low-frequency emphasis signal e1 by adding the delayed sound signal d1 and the low-frequency signal c4. The low-frequency emphasis signal e1 is a signal in which the low frequency components of the input sound signal a1 are emphasized. The combination of the delay unit 23 and the synthesis unit 24 is an example of a "second generation unit."

[0047] The amplifier 30 amplifies the low-frequency emphasis signal e1 to a level suitable for driving a speaker, and outputs the amplified sound signal e2 to the speaker device 40.

[0048] The speaker device 40 emits a sound corresponding to the amplified sound signal e2.

[0049] A2: Summary of the first embodiment As described above, the bass emphasis method according to the first embodiment includes extracting a percussion signal b2 from an input sound signal a1, generating a low-frequency signal c4 based on the percussion signal b2, and generating a bass emphasis signal e1 based on the low-frequency signal c4 and the input sound signal a1. The input sound signal a1 is a signal including harmonic instrument sound components and non-harmonic instrument sound components. The low-frequency signal c4 is a signal having a frequency half the frequency of the fundamental wave component of the percussion signal b2. The bass emphasis signal e1 is a signal in which the low frequency components of the input sound signal a1 are emphasized.

[0050] In order to emphasize the bass of the harmonic instrument sound components, if a bass signal having a frequency half the frequency of the fundamental wave component of the harmonic instrument sound components is generated and added to the original harmonic instrument sound components, the harmonic instrument sound components to which the bass signal has been added may not have overtones of the bass signal. In addition, since the harmonic instrument sound components are sustained sounds, the harmonic instrument sound components to which the bass signal has been added may be recognized as unnaturally distorted sounds. On the other hand, since the non-harmonic instrument sound components have random frequency components compared to the harmonic instrument sound components and are non-sustained sounds, even if the bass of the non-harmonic instrument sound components is emphasized, it is difficult to recognize it as distortion. Therefore, according to this method, the bass of the harmonic instrument sound components is not emphasized, so the occurrence of distortion is suppressed. In addition, since the bass of the non-harmonic instrument sound components is emphasized, the sense of power and the sense of beat can be increased.

[0051] In the bass emphasis method according to the first embodiment, the non-harmonic instrument sound components include percussion instrument sound components.

[0052] Since percussion sound components have more random frequency components than harmonic instrument sound components and are non-sustained sounds, even if the bass of the percussion sound components is emphasized, it is difficult to recognize it as distortion. Therefore, according to this method, the bass of the harmonic instrument sound components is not emphasized, but the bass of the percussion sound components is emphasized, thereby enhancing the sense of power and beat.

[0053] In the bass enhancement method according to the first embodiment, extracting the percussion signal b2 from the input sound signal a1 includes generating a first bass signal b1 from the input sound signal a1 and extracting the percussion signal b2 from the first bass signal b1. The first bass signal b1 is a signal in which higher frequency components than the frequency band of the percussion sound components are reduced.

[0054] According to this method, the percussion signal b2 is extracted from the first bass signal b1 with reduced high-frequency components. Therefore, the amount of calculation required to extract the percussion signal b2 is less than the amount of calculation required to extract the percussion signal b2 from the input sound signal a1 before the high-frequency components are reduced, and the calculation load is reduced.

[0055] In the bass enhancement method according to the first embodiment, generating a low-frequency signal c4 based on the percussion signal b2 includes generating a second bass signal c1 from the percussion signal b2 and generating a low-frequency signal c4 from the second bass signal c1. The second bass signal c1 is a signal in which higher frequency components than the frequency band of the percussion sound components are reduced.

[0056] According to this method, only the low frequency components of the percussion sound components are emphasized, so that the sense of power and beat can be enhanced.

[0057] In the bass emphasis method according to the first embodiment, generating the bass emphasis signal e1 includes generating a delayed sound signal d1 and adding the delayed sound signal d1 and the low-frequency signal c4 to generate the bass emphasis signal e1. The delayed sound signal d1 is a signal obtained by delaying the input sound signal a1 by the time required to generate the low-frequency signal c4 based on the input sound signal a1.

[0058] According to this method, the phase relationship between the low-frequency signal c4 and the input sound signal a1 can be adjusted, so that sound with less distortion and more powerful and beat-like feel can be reproduced.

[0059] The bass emphasis device 20 according to the first embodiment includes an extraction unit 21, a generation unit 22, a delay unit 23, and a synthesis unit 24. The extraction unit 21 extracts a percussion signal b2 from an input sound signal a1. The generation unit 22 generates a low-frequency signal c4 based on the percussion signal b2. The synthesis unit 24 generates a bass emphasis signal e1 based on the low-frequency signal c4 and the input sound signal a1.

[0060] According to this embodiment, the bass of the harmonic instrument sound components is not emphasized, so that the occurrence of distortion is suppressed, and the bass of the percussion instrument sound components is emphasized, so that the sense of power and the sense of beat can be enhanced.

[0061] In the first embodiment, the percussion sound components are an example of "non-harmonic instrument sound components", the percussion signal b2 is an example of a "non-harmonic instrument signal", the generation unit 22 is an example of a "first generation unit", and the combination of the delay unit 23 and the synthesis unit 24 is an example of a "second generation unit".

[0062] B: Variation The present invention is not limited to the above embodiment, and various modified examples can be adopted within the scope of the present invention. Specific modified examples are exemplified below. Two or more aspects arbitrarily selected from the following examples can be appropriately combined within a range that does not contradict each other. In the modified examples exemplified below, the symbols used in the above explanation are used for elements whose actions and functions are equivalent to those of the above embodiment, and detailed explanations of each are appropriately omitted.

[0063] B1: First modified example Hereinafter, an audio system according to the first modification will be described with reference to Fig. 10. In the following description, for the sake of simplicity, the same reference numerals are used for the same components as those in the first embodiment, and the description of their functions may be omitted. In the following description, for the sake of simplicity, the differences between the first modification and the first embodiment will be mainly described.

[0064] 10 is a configuration diagram showing an example of an audio system 1A including a bass emphasis device 20A according to a first modified example. The audio system 1A is mounted on a vehicle such as an automobile, similar to the audio system 1 according to the first embodiment. The audio system 1A includes a storage device 10A, a bass emphasis device 20A, an amplifier device 30, a speaker device 40, and an actuator 50.

[0065] The storage device 10A is a computer-readable recording medium. The storage device 10A includes a non-volatile memory and a volatile memory. The non-volatile memory is, for example, a ROM, an EPROM, and an EEPROM. The volatile memory is, for example, a RAM.

[0066] The storage device 10A stores a program p2 and various information. The program p2 defines the operation of the bass enhancement device 20A. The storage device 10A may store the program p2 read from a storage device in a server (not shown). In this case, the storage device in the server is an example of a computer-readable recording medium.

[0067] The bass emphasis device 20A reads the program p2 from the storage device 10A. By executing the program p2, the bass emphasis device 20A functions as an extraction unit 21, a generation unit 22, a delay unit 23, a synthesis unit 24, and an output unit 25. At least one of the extraction unit 21, the generation unit 22, the delay unit 23, the synthesis unit 24, and the output unit 25 may be realized by a circuit such as a DSP, an ASIC, a PLD, or an FPGA.

[0068] The extraction unit 21, the generation unit 22, the delay unit 23, and the synthesis unit 24 have the same configurations as the extraction unit 21, the generation unit 22, the delay unit 23, and the synthesis unit 24 in FIG. 1, and therefore their description will be omitted.

[0069] The output section 25 outputs to the actuator 50 an output sound signal f1 including a low-frequency signal c4.

[0070] The actuator 50 is provided on a seat cushion 61 of a vehicle seat 60. The actuator 50 has, for example, a magnet fixed to a case via a damper, a yoke fixed directly to the case, and a coil wound around the yoke. A current corresponding to the output sound signal f1 flows through the coil. A force is generated along the axis of the coil due to the action of the current flowing through the coil according to the output sound signal f1 and the magnetic field generated by the magnet. Therefore, as the output sound signal f1 changes, the yoke and the coil vibrate along the axis of the coil relative to the magnet. With the above configuration, the actuator 50 vibrates the seat cushion 61 based on the output sound signal f1.

[0071] As described above, the bass emphasis device 20A according to the first modification includes the extraction unit 21, the generation unit 22, and the output unit 25. The extraction unit 21 extracts the percussion signal b2 from the input sound signal a1. The input sound signal a1 is a signal including a harmonic instrument sound component and a percussion instrument sound component. The percussion signal b2 is a signal indicating the percussion instrument sound component. The generation unit 22 generates a low-frequency signal c4 based on the percussion signal b2. The low-frequency signal c4 is a signal having a frequency half the frequency of the fundamental wave component of the percussion signal b2. The output unit 25 outputs the output sound signal f1 to the actuator 50. The output sound signal f1 is a signal including the low-frequency signal c4.

[0072] According to this embodiment, the bass enhancement device 20A can apply vibrations corresponding to the output sound signal f1 to the body of the passenger sitting on the seat 60 by vibrating the seat cushion 61. Therefore, the passenger can feel the power and the beat not only through his / her ears but also through his / her whole body. Therefore, the passenger can feel the power and the beat more strongly.

[0073] The actuator 50 is not limited to an actuator having a damper with the above-described configuration, and may be, for example, a speaker capable of reproducing low-frequency sounds, such as a woofer.

[0074] The actuator 50 may also be provided in a seat back 62 of the seat 60 .

[0075] Furthermore, the acoustic system 1A according to the first modification is mounted on a vehicle such as an automobile, and the actuator 50 vibrates the seat cushion 61 of the seat 60 in response to the output sound signal f1, but the acoustic system 1A may also be applied to a building such as a house. In this case, the actuator 50 may be disposed on a sofa, a chair, a cushion, or the like.

[0076] B2: Second variant In the first modified example, a low-frequency signal c4 is input to the output unit 25. However, instead of the low-frequency signal c4, the output unit 25 may output to the actuator 50 a low-frequency emphasis signal e1 that is a combination of the low-frequency signal c4 and the input sound signal a1.

[0077] B3: Third variant In the first embodiment, HPSS is used to extract the percussion sound components, but the method of extracting the percussion sound components is not limited to the method using HPSS, and various extraction methods may be used. For example, a well-known sound source separation technique may be used to extract the percussion sound components. A known sound source separation technique is a technique that separates vocal sounds and each of the instrument sounds from a music signal in which vocal sounds and multiple instrument sounds are mixed, based on deep learning using a neural network.

[0078] For example, a technology called Demucs developed by Facebook Research uses a recurrent neural network based on the U-Net architecture to analyze the temporal structure of a music signal. The analysis results are input to a convolutional neural network, which separates each sound source in the frequency domain. The spectrograms of each separated sound source are then inverse Fourier transformed to restore the waveform in the time domain (https: / / github.com / facebookresearch / demucs).

[0079] By applying the above sound source separation technology, it is possible to extract percussion sound components.

[0080] B4: Fourth variant In the first embodiment, the extraction section 21 is provided with a low-pass filter 211 in front of the percussion sound extraction section 212. The low-pass filter 211 has the purpose of reducing high-frequency components unnecessary for the calculation in the percussion sound extraction section 212, thereby reducing the amount of calculation processing in the percussion sound extraction section 212. For this reason, the low-pass filter 211 may be omitted.

[0081] B5: Fifth variant In the generating section 22 of the first embodiment, a signal having a frequency that is 1 / 2 the frequency of the fundamental component of the percussion signal b2 is generated as the low-frequency signal c4, but the low-frequency signal c4 may be a signal having a frequency that is 1 / N (N is an integer equal to or greater than 3) of the frequency of the fundamental component of the percussion signal b2. For example, the generating section of the fifth modified example generates a signal having a frequency that is 1 / 4 the frequency of the fundamental component of the percussion signal b2 as the low-frequency signal c4.

[0082] According to this embodiment, a signal with emphasized low frequencies is generated, which can further enhance the sense of power and beat.

[0083] B6: 6th variant Furthermore, the audio system 1 according to the first embodiment is mounted on a vehicle such as an automobile, but the audio system 1 is also applicable to the fields of home audio and professional audio.

[0084] C: Notes From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0085] A bass emphasis method according to one aspect (aspect 1) of the present disclosure includes: extracting a non-harmonic instrument signal indicative of a non-harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components; generating a low-frequency signal having a frequency that is 1 / N (N is an integer equal to or greater than 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal; and generating a bass emphasis signal in which the low-frequency components of the input sound signal are emphasized based on the low-frequency signal and the input sound signal.

[0086] In order to emphasize the bass of the harmonic instrument sound components, if a bass signal having a frequency 1 / N of the frequency of the fundamental wave component of the harmonic instrument sound components is generated and added to the original harmonic instrument sound components, the harmonic instrument sound components to which the bass signal has been added may not have overtones of the bass signal. In addition, since the harmonic instrument sound components are sustained sounds, the harmonic instrument sound components to which the bass signal has been added may be recognized as unnaturally distorted sounds. On the other hand, since the non-harmonic instrument sound components have random frequency components and are less sustained sounds than the harmonic instrument sound components, even if the bass of the non-harmonic instrument sound components is emphasized, it is difficult to recognize it as distortion. Therefore, according to this embodiment, the bass of the harmonic instrument sound components is not emphasized, so the occurrence of distortion is suppressed. In addition, since the bass of the non-harmonic instrument sound components is emphasized, the sense of power and the sense of beat can be increased.

[0087] In the bass emphasis method according to one aspect (aspect 2) of the present disclosure, the non-harmonic instrument sound components include percussion instrument sound components.

[0088] Since percussion sound components have more random frequency components than harmonic instrument sound components and are non-sustained sounds, even if the bass of the percussion sound components is emphasized, it is difficult to recognize it as distortion. Therefore, according to this aspect, the bass of the harmonic instrument sound components is not emphasized, but the bass of the percussion sound components is emphasized, thereby enhancing the sense of power and beat.

[0089] In a bass emphasis method according to one aspect (aspect 3) of the present disclosure, extracting the non-harmonic instrument signal from the input sound signal includes generating a first bass signal from the input sound signal by reducing high-frequency components from the input sound signal below the frequency band of the non-harmonic instrument sound components, and extracting the non-harmonic instrument signal from the first bass signal.

[0090] According to this aspect, the inharmonic musical instrument signal is extracted from the first bass signal with the high frequency components reduced, and therefore the amount of calculation required for the extraction is reduced compared to the amount of calculation required for extracting the inharmonic musical instrument signal from the input sound signal before the high frequency components are reduced, thereby reducing the calculation load.

[0091] In a bass enhancement method according to one aspect (aspect 4) of the present disclosure, generating the low-frequency signal based on the non-harmonic instrument signal includes generating a second bass signal from the non-harmonic instrument signal by reducing higher frequency components than the frequency band of the non-harmonic instrument sound components, and generating the low-frequency signal from the second bass signal.

[0092] According to this embodiment, only the low frequency components of the non-harmonic instrument sound components are emphasized, so that the sense of power and beat can be further enhanced.

[0093] In a bass emphasis method according to one aspect (aspect 5) of the present disclosure, generating the bass emphasis signal includes generating a delayed sound signal by delaying the input sound signal by a time required to generate the low-frequency signal based on the input sound signal, and generating the bass emphasis signal by adding the delayed sound signal and the low-frequency signal.

[0094] According to this aspect, the phase relationship between the low-frequency signal and the input sound signal can be adjusted, so that sound with less distortion and more powerful and beatful sound can be reproduced.

[0095] A bass emphasis device according to one aspect (aspect 6) of the present disclosure includes an extraction unit that extracts a non-harmonic instrument signal indicative of a non-harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components, a first generation unit that generates a low-frequency signal having a frequency that is 1 / N (N is an integer greater than or equal to 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal, and a second generation unit that generates a bass emphasis signal in which the low-frequency components of the input sound signal are emphasized based on the low-frequency signal and the input sound signal.

[0096] According to this embodiment, the bass of the harmonic musical instrument sound components is not emphasized, so that the occurrence of distortion is suppressed, whereas the bass of the non-harmonic musical instrument sound components is emphasized, so that the sense of power and the sense of beat can be enhanced.

[0097] A bass emphasis device according to one aspect (aspect 7) of the present disclosure includes an extraction unit that extracts a non-harmonic instrument signal indicative of a harmonic instrument sound component from an input sound signal including harmonic instrument sound components and non-harmonic instrument sound components other than the harmonic instrument sound components, a generation unit that generates a low-frequency signal having a frequency that is 1 / N (N is an integer greater than or equal to 2) of a fundamental wave component of the non-harmonic instrument sound signal based on the non-harmonic instrument signal, and an output unit that outputs an output sound signal including at least the low-frequency signal to an actuator that vibrates a seat.

[0098] According to this aspect, the seat is vibrated by a signal in which the bass of the non-harmonic instrument sound components is emphasized, so that the sense of power and the feeling of beat can be further enhanced. [Explanation of symbols]

[0099] 20...bass emphasis device, 21...extraction section, 22...generation section, 23...delay section, 24...synthesis section, 25...output section, 50...actuator, 60...seat, a1...input sound signal, b1...first bass signal, b2...percussion signal, c1...second bass signal, c4...low frequency signal, e1...bass emphasis signal, d1...delayed sound signal.

Claims

1. extracting a non-harmonic instrument signal indicative of a harmonic instrument sound component from an input sound signal including the harmonic instrument sound component and a non-harmonic instrument sound component other than the harmonic instrument sound component; generating a low-frequency signal based on the non-harmonic musical instrument signal, the low-frequency signal having a frequency that is 1 / N (N is an integer equal to or greater than 2) of a frequency of a fundamental component of the non-harmonic musical instrument signal; generating a low-frequency emphasized signal in which a low-frequency component of the input sound signal is emphasized based on the low-frequency signal and the input sound signal; Bass emphasis method.

2. the non-harmonic instrument sound components include percussion instrument sound components; The method for enhancing bass sound according to claim 1 .

3. Extracting the non-harmonic musical instrument signal from the input sound signal comprises: generating a first bass signal by reducing frequency components higher than a frequency band of the non-harmonic musical instrument sound components from the input sound signal; extracting the non-harmonic musical instrument signal from the first bass signal. The method for enhancing bass sound according to claim 1 .

4. generating the low frequency signal based on the non-harmonic musical instrument signal, generating a second bass signal from the non-harmonic musical instrument signal by reducing frequency components higher than a frequency band of the non-harmonic musical instrument sound components; generating the low frequency signal from the second bass signal; The method for enhancing bass sound according to claim 1 .

5. The generating of the low frequency boost signal includes: generating a delayed sound signal by delaying the input sound signal by a time period required for generating the low-frequency signal based on the input sound signal; generating the low-frequency emphasis signal by adding the delayed sound signal and the low-frequency signal; The method for enhancing bass tones according to any one of claims 1 to 3.

6. an extracting unit that extracts a non-harmonic instrument signal representing a harmonic instrument sound component from an input sound signal including the harmonic instrument sound component and a non-harmonic instrument sound component other than the harmonic instrument sound component; a first generator for generating a low-frequency signal having a frequency that is 1 / N (N is an integer equal to or greater than 2) of a frequency of a fundamental component of the non-harmonic musical instrument signal based on the non-harmonic musical instrument signal; a second generation unit that generates a low-frequency emphasized signal in which a low-frequency component of the input sound signal is emphasized based on the low-frequency signal and the input sound signal, Bass emphasis device.

7. an extracting unit that extracts a non-harmonic instrument signal representing a harmonic instrument sound component from an input sound signal including the harmonic instrument sound component and a non-harmonic instrument sound component other than the harmonic instrument sound component; a generator for generating a low-frequency signal having a frequency that is 1 / N (N is an integer equal to or greater than 2) of a frequency of a fundamental component of the non-harmonic musical instrument signal based on the non-harmonic musical instrument signal; and an output unit that outputs an output sound signal including at least the low-frequency signal to an actuator that vibrates the seat. Bass emphasis device.

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