Signal processor, method, program, and cognitive function improvement system

Abstract

To perform amplitude modulation of acoustic signals while suppressing degradation of acoustic experience.SOLUTION: A signal processor of an aspect of the present disclosure is provided with means for: receiving an input acoustic signal; obtaining a first acoustic signal having an amplitude change corresponding to a predetermined frequency by amplitude modulating a first partial signal included in the input acoustic signal; obtaining a second acoustic signal having an amplitude change corresponding to the predetermined frequency and different in phase from the first acoustic signal by amplitude modulating a second partial signal included in the input acoustic signal; and outputting an output acoustic signal based on the obtained first acoustic signal and the second acoustic signal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a signal processing device, a method, a program, and a system for improving cognitive function. [Background technology]

[0002] There is a research report that showing that inducing gamma waves in the brain of an organism by subjecting it to pulsating sound stimuli at a frequency of about 40 times per second is effective in improving the organism's cognitive function (see Non-Patent Document 1). Gamma waves refer to neural oscillations that capture periodic neural activity in the brain's cortex using electrophysiological techniques such as electroencephalography and magnetoencephalography, and whose frequencies fall within the gamma band (25 to 140 Hz).

[0003] Patent document 1 discloses adjusting the volume by increasing or decreasing the amplitude of sound waves or sound tracks to create rhythmic stimulation corresponding to the stimulation frequency for inducing brainwave entrainment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2020-501853 [Non-patent literature]

[0005] [Non-Patent Document 1] Multi-sensory Gamma Stimulation Ameliorates Alzheimer's-Associated Pathology and Improves Cognition Cell 2019 Apr 4;177(2):256-271.e22. doi: 10.1016 / j.cell.2019.02.014. Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the volume of an audio signal is increased or decreased significantly in a short period as in the technique of Patent Document 1, the naturalness of how the sound is heard may be lost, causing discomfort to the listener.

[0007] An object of the present disclosure is to amplitude modulate an audio signal while minimizing degradation of the audio experience. [Means for solving the problem]

[0008] A signal processing device according to one embodiment of the present disclosure includes a means for accepting an input acoustic signal, a means for amplitude-modulating a first partial signal included in the input acoustic signal to obtain a first acoustic signal having an amplitude change corresponding to a predetermined frequency, a means for amplitude-modulating a second partial signal included in the input acoustic signal to obtain a second acoustic signal having an amplitude change corresponding to a predetermined frequency and having a phase different from that of the first acoustic signal, and a means for outputting an output acoustic signal based on the obtained first and second acoustic signals. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of an audio system according to an embodiment of the present invention. [Diagram 2] 1 is a block diagram showing a configuration of a signal processing device according to an embodiment of the present invention; [Diagram 3] FIG. 1 is an explanatory diagram of one aspect of the present embodiment. [Figure 4] FIG. 2 is a diagram showing an overall flow of acoustic signal processing by the signal processing device of the present embodiment. [Diagram 5] 1 is an explanatory diagram of a plurality of partial signals having different frequency characteristics; [Figure 6] 1 is an explanatory diagram of a plurality of partial signals having different qualitative characteristics of sound; [Figure 7] 1 is an explanatory diagram of a plurality of partial signals having different output characteristics; [Figure 8] 13 is a graph showing experimental results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings for explaining the embodiment, the same components are generally designated by the same reference numerals, and the repeated description will be omitted.

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings for explaining the embodiment, the same components are generally designated by the same reference numerals, and the repeated description will be omitted.

[0012] (1) Sound system configuration The configuration of the audio system of this embodiment will be described below. Fig. 1 is a block diagram showing the configuration of the audio system of this embodiment.

[0013] As shown in FIG. 1, the audio system 1 includes a signal processing device 10, an audio output device 30, and a sound source device 50.

[0014] The signal processing device 10 and the sound source device 50 are connected to each other via a predetermined interface capable of transmitting an audio signal. The interface is, for example, SPDIF (Sony Philips Digital Interface), HDMI (registered trademark) (High-Definition Multimedia Interface), a pin connector (RCA pin), or an audio interface for headphones. The interface may be a wireless interface using Bluetooth (registered trademark) or the like. Similarly, the signal processing device 10 and the audio output device 30 are connected to each other via a predetermined interface. The audio signal in this embodiment includes either or both of an analog signal and a digital signal.

[0015] The signal processing device 10 performs audio signal processing on an input audio signal acquired from a sound source device 50. The audio signal processing by the signal processing device 10 includes at least an audio signal modulation process (described in detail below). The audio signal processing by the signal processing device 10 may also include an audio signal conversion process (e.g., separation, extraction, or synthesis). Furthermore, the audio signal processing by the signal processing device 10 may further include an audio signal amplification process similar to that of an AV amplifier, for example. The signal processing device 10 sends an output audio signal generated by the audio signal processing to the audio output device 30. The signal processing device 10 is an example of an information processing device.

[0016] The audio output device 30 generates a sound according to the output audio signal acquired from the signal processing device 10. The audio output device 30 is, for example, a loudspeaker (which may include a speaker with a built-in amplifier (powered speaker)), a headphone, or an earphone. The sound output device 30 can be configured as one device together with the signal processing device 10. Specifically, the signal processing device 10 and the sound output device 30 can be implemented in a TV, a radio, a music player, an AV amplifier, a speaker, a headphone, an earphone, a smartphone, or a PC. The signal processing device 10 and the sound output device 30 configure a cognitive function improvement system. The sound output device 30 induces gamma waves in the user's brain (i.e., improves the intensity of brain waves in the gamma band) or causes synchronization (i.e., improves the synchronization of brain waves with respect to frequencies in the gamma band) by making the user (listener) hear a sound corresponding to the output sound signal output by the signal processing device 10, or causes both.

[0017] The sound source device 50 transmits an input sound signal to the signal processing device 10. The sound source device 50 is, for example, a TV, a radio, a music player, a smartphone, a PC, a musical instrument, a microphone, a telephone, a game machine, an amusement machine, or a device that transmits a sound signal by broadcasting or information communication.

[0018] (1-1) Configuration of the signal processing device The configuration of the signal processing device will be described below with reference to Fig. 2, which is a block diagram showing the configuration of the signal processing device of this embodiment.

[0019] 2, the signal processing device 10 includes a storage device 11, a processor 12, an input / output interface 13, and a communication interface 14. The signal processing device 10 is connected to a display 21.

[0020] The storage device 11 is configured to store programs and data. The storage device 11 is, for example, a combination of a Read Only Memory (ROM), a Random Access Memory (RAM), and a storage (for example, a flash memory or a hard disk). The programs and data may be provided via a network, or may be provided by recording them on a computer-readable recording medium.

[0021] The programs include, for example, the following programs: ·OS (Operating System) programs Application programs that perform information processing

[0022] The data includes, for example, the following data: Databases referenced in information processing Data obtained by performing information processing (i.e., the results of performing information processing)

[0023] The processor 12 is a computer that realizes the functions of the signal processing device 10 by reading and executing a program stored in the storage device 11. At least a part of the functions of the signal processing device 10 may be realized by one or more dedicated circuits. The processor 12 is, for example, at least one of the following: ·CPU(Central Processing Unit) ·GPU(Graphic Processing Unit) ·ASIC(Application Specific Integrated Circuit) ·FPGA(Field Programmable Gate Array) ·DSP(Digital Signal Processor)

[0024] The input / output interface 13 is configured to obtain user instructions from an input device connected to the signal processing device 10 , and to output information to an output device connected to the signal processing device 10 . The input device is, for example, a sound source device 50, a physical button, a keyboard, a pointing device, a touch panel, or a combination thereof. The output device is, for example, a display 21, an audio output device 30, or a combination thereof.

[0025] Furthermore, the input / output interface 13 may include signal processing hardware, such as, for example, an A / D converter, a D / A converter, an amplifier, a mixer, a filter, and the like.

[0026] The communication interface 14 is configured to control communication between the signal processing device 10 and an external device (eg, the audio output device 30 or the audio source device 50).

[0027] The display 21 is configured to display an image (still image or moving image). The display 21 is, for example, a liquid crystal display or an organic EL display.

[0028] (2) One aspect of the embodiment An embodiment of the present invention will now be described with reference to Fig. 3, which is an explanatory diagram of an embodiment of the present invention.

[0029] The signal processing device 10 acquires an input acoustic signal from a sound source device 50. As shown in Fig. 3, the signal processing device 10 acquires a plurality of partial signals including a first partial signal and a second partial signal based on the input acoustic signal. In the example of Fig. 3, the first partial signal includes an acoustic signal obtained by extracting a component of a first frequency band from the input acoustic signal, and the second partial signal includes an acoustic signal obtained by extracting a component of a second frequency band different from the first frequency band from the input acoustic signal.

[0030] The signal processing device 10 generates a modulated first partial signal by modulating the first partial signal. The signal processing device 10 performs modulation without intentionally adding delay or attenuation to the first partial signal. The modulation is amplitude modulation using a first modulation function (periodic function) having a frequency of, for example, 17.5 Hz to 22.5 Hz, i.e., approximately 20 Hz. The amplitude modulation is an operation that changes the macroscopic volume strength, that is, the magnitude of the envelope, using a periodic function. As a result, a change in amplitude (volume strength) corresponding to the above frequency is added to the first partial signal.

[0031] The signal processing device 10 generates a modulated second partial signal by modulating the second partial signal. The signal processing device 10 performs modulation without intentionally adding delay or attenuation to the second partial signal. The modulation is amplitude modulation using a second modulation function (periodic function) having a frequency of, for example, 17.5 Hz to 22.5 Hz, i.e., approximately 20 Hz. As a result, a change in amplitude (volume strength) corresponding to the above frequency is added to the second partial signal.

[0032] The signal processing device 10 generates an output acoustic signal based on a plurality of modulated partial signals (i.e., a modulated first partial signal and a modulated second partial signal). The signal processing device 10 sends the output acoustic signal to the acoustic output device 30. The acoustic output device 30 generates a sound according to the output acoustic signal.

[0033] A user US1 (an example of a "listener") listens to the sound emitted from the acoustic output device 30. The user US1 is, for example, a dementia patient, a person with mild cognitive impairment (MCI), or a healthy person who expects to prevent dementia, prevent cognitive decline, or improve cognitive function. As described above, the output acoustic signal is based on the modulated first partial signal and the modulated second partial signal described above.

[0034] In the example of FIG. 3, the second modulation function is determined to have the same frequency as the first modulation function, but a phase different by 180 degrees. That is, the envelope of the amplitude waveform of the modulated first partial signal (hereinafter simply referred to as the "envelope") and the envelope of the modulated second partial signal both have volume fluctuations corresponding to approximately 20 Hz, but the timing of one peak point is shifted from the other peak point by approximately 25 ms. That is, when focusing on the partial signals of each frequency band included in the output acoustic signal, the points (peaks) where the volume of the first frequency band becomes stronger and the points where the volume of the second frequency band becomes stronger appear alternately at approximately equal intervals every 1 / 40th of a second. Similarly, when focusing on the partial signals of each frequency band included in the output acoustic signal, the points (valleys) where the volume of the first frequency band becomes weaker and the points where the volume of the second frequency band becomes weaker appear alternately at approximately equal intervals every 1 / 40th of a second. In this example, if the waveform of the modulation function is symmetrical like a sine wave (i.e., the rising and falling waveforms are identical), the timing of the volume peaks in the first frequency band and the volume troughs in the second frequency band will match, and the timing of the volume troughs in the first frequency band and the volume peaks in the second frequency band will match, thereby suppressing fluctuations in the volume of the output sound when viewed across all frequency bands.

[0035] In addition, sound waves that enter the human eardrum or enter the cochlea directly through bone conduction are mechanically frequency-decomposed or phase-synchronized by the cochlea, converted into nerve pulses by hair cells, and finally reach the temporal lobe of the cerebrum. The temporal lobe has an arrangement called a "tonotopy map," which determines the corresponding frequency depending on the part. That is, for example, nerve pulses caused by sounds in the first frequency band and nerve pulses caused by sounds in the second frequency band can be transmitted to different parts of the auditory cortex. In this case, each part of the auditory cortex is active at approximately 20 Hz, but since the activity of each part is shifted by half a cycle, the auditory cortex as a whole is active at approximately 40 Hz.

[0036] In this way, when a listener listens to the sound emitted from the sound output device 30, gamma waves are induced or synchronized in the listener's brain. This is expected to have an effect of improving the listener's cognitive function (for example, treating or preventing dementia). On the other hand, in the output sound signal, the portion where the volume of the first frequency band becomes louder and the portion where the volume of the second frequency band becomes louder, and the portion where the volume of the first frequency band becomes quieter and the portion where the volume of the second frequency band becomes quieter are different from each other, so the difference between the maximum volume and the minimum volume of the sound emitted from the sound output device 30 is suppressed compared to when these are the same. Therefore, deterioration of the listener's sound experience is suppressed (the listener is less likely to feel uncomfortable).

[0037] (3) Acoustic signal processing The acoustic signal processing of this embodiment will be described. Fig. 4 is a diagram showing the overall flow of acoustic signal processing by the signal processing device of this embodiment. Fig. 5 is an explanatory diagram of a plurality of partial signals having different frequency characteristics. Fig. 6 is an explanatory diagram of a plurality of partial signals having different sound qualitative characteristics. Fig. 7 is an explanatory diagram of a plurality of partial signals having different output characteristics.

[0038] 4 is realized by the processor 12 of the signal processing device 10 reading and executing a program stored in the storage device 11. At least a part of the processing in FIG. 4 may be realized by one or more dedicated circuits.

[0039] The acoustic signal processing in FIG. 4 starts when any one of the following start conditions is met. The acoustic signal processing in Figure 4 was called by another process or an external instruction. The user performed an operation to call up the acoustic signal processing shown in Figure 4. The signal processing device 10 is in a predetermined state (for example, power is turned on). The appointed time has arrived. A predetermined time has elapsed since a predetermined event (eg, start-up of the signal processing device 10 or the previous execution of the acoustic signal processing of FIG. 4).

[0040] As shown in FIG. 4, the signal processing device 10 acquires an input sound signal (S110). Specifically, the signal processing device 10 receives an input acoustic signal sent from a sound source device 50 . In step S110, the signal processing device 10 may further perform A / D conversion of the input acoustic signal.

[0041] The input acoustic signal may, for example, correspond to at least one of the following: Musical content (e.g., singing, playing, or a combination thereof (i.e., music). This may include audio content that accompanies video content.) Audio content (e.g., audio of a reading, narration, announcement, radio play, monologue, conversation, monologue, or any combination thereof. This may include audio content that accompanies video content.) Other audio content (e.g. electronic, environmental, or mechanical sounds) However, singing, or audio content, is not limited to sounds produced by the human vocal tract, but may also include sounds generated by voice synthesis technology.

[0042] After step S110, the signal processing device 10 executes acquisition of a partial signal (S111). Specifically, the signal processing device 10 acquires a plurality of partial signals based on the input acoustic signal acquired in step S110.

[0043] The number of partial signals is an arbitrary integer equal to or greater than two. The partial signals differ from each other in at least one feature. For example, one of the partial signals has a predetermined feature, and the remaining partial signals do not have the feature. Alternatively, one of the partial signals is qualitatively or quantitatively superior in a predetermined feature, and the remaining partial signals are qualitatively or quantitatively inferior in the feature. The feature may be determined based on an input operation by a user (listener) or another person, or an instruction from outside, or may be determined by an algorithm. For example, the signal processing device 10 may determine features for generating a plurality of partial signals based on a result of analyzing an input acoustic signal.

[0044] In the following description, the other person may be, for example, at least one of the following people: Your family, friends, or acquaintances Healthcare professionals (e.g. your doctor) Creator or provider of the content corresponding to the input audio signal Provider of the signal processing device 10 - Administrator of the facility used by the user

[0045] The characteristics may be, for example, at least one of the following: Frequency characteristics Sound characteristics (especially qualitative characteristics) Amplitude characteristics Output Features

[0046] The frequency characteristic is, for example, an acoustic component that satisfies one or more frequency conditions. Specifically, as shown in FIG. 5, the first partial signal includes acoustic components in odd-numbered frequency bands counting from the low frequency side among the multiple divided frequency bands (subbands). On the other hand, the second partial signal includes acoustic components in even-numbered frequency bands counting from the low frequency side among the multiple divided frequency bands. The first frequency band corresponds to a frequency range less than f1. The second frequency band corresponds to a frequency range equal to or greater than f1 and less than f2. The third frequency band corresponds to a frequency range equal to or greater than f2 and less than f3. The fourth frequency band corresponds to a frequency range equal to or greater than f3 and less than f4. The fifth frequency band corresponds to a frequency range equal to or greater than f4 and less than f5. As an example, the signal processing device 10 may generate multiple frequency bands by dividing the input acoustic signal by 1 / 3 octave or by one octave.

[0047] The sound features are, for example, sound components that satisfy one or more sound quality conditions. The sound quality conditions may be, for example, conditions related to at least one of the following: The type of audio source (e.g. object, instrument, vocal, music, dialogue, or input channel) - Direction of sound arrival (direction of sound source) Location of sound recording (e.g. which of multiple microphones recorded the sound) -Improvement of cognitive function or prevention of dementia In the example of FIG. 6, the first partial signal includes an acoustic component having a sound source of a musical instrument, and the second partial signal includes an acoustic component having a sound source of a vocal.

[0048] An amplitude feature is, for example, a sound component that satisfies one or more amplitude conditions. For example, an amplitude feature is that the change in volume over time matches a predetermined pattern.

[0049] The output feature is, for example, a sound (acoustic component) that a listener perceives as coming from a sound source in a given direction or position. Specifically, the output feature is, for example, an acoustic component that satisfies one or more output conditions. As a first example, the output condition is that the signal is associated with a speaker in a specific direction constituting a surround system as the audio output device 30 (i.e., is ultimately output from a specific speaker). In the example of Fig. 7, the audio output device 30 corresponds to a surround speaker system including speakers 30-1 to 30-4. The first partial signal is associated with speakers 30-3 and 30-4 in a specific direction (i.e., is output from the left rear or right rear), and the second partial signal is not associated with the speakers 30-3 and 30-4 (instead, is associated with speakers 30-1 and 30-2 (i.e., is output from the left front or right front)). As a second example, an output condition may be that the sound signal is associated with a virtual sound source set in a particular direction or position in object audio.

[0050] If the input acoustic signal acquired in step S110 has been previously separated into a plurality of partial signals that differ from each other in at least one characteristic (for example, if the input acoustic signal corresponds to a multi-channel acoustic signal associated with each speaker that constitutes a surround system as the acoustic output device 30), step S111 can be omitted. On the other hand, if the input acoustic signal has not been previously separated into a plurality of partial signals that differ from each other in at least one characteristic, the signal processing device 10 converts the input acoustic signal into a plurality of partial signals. For example, the signal processing device 10 extracts or separates an acoustic signal having a predetermined characteristic from the input acoustic signal.

[0051] After step S111, the signal processing device 10 performs modulation of the partial signal (S112). Specifically, the signal processing device 10 modulates the multiple partial signals acquired in step S111. First, the signal processing device 10 assigns each of the multiple partial signals to one of M groups. M is an arbitrary integer equal to or greater than 2, but is assumed to be equal to 2 in the following description. The number of partial signals assigned to each group is an arbitrary integer equal to or greater than 1.

[0052] 5, the signal processing device 10 assigns first partial signals corresponding to odd-numbered frequency bands to a first group, and assigns second partial signals corresponding to even-numbered frequency bands to a second group.

[0053] The signal processing device 10 performs amplitude modulation on the partial signals belonging to each group using a modulation function having a frequency (hereinafter referred to as a "predetermined frequency") that is approximately 1 / M of the frequency corresponding to gamma waves (for example, a frequency between 35 Hz and 45 Hz). That is, when M=2, the predetermined frequency is approximately 20 Hz (between 17.5 Hz and 22.5 Hz), when M=3, the predetermined frequency is approximately 13.3 Hz (between 11.7 Hz and 15 Hz), and when M=4, the predetermined frequency is approximately 10 Hz (between 8.8 Hz and 11.3 Hz).

[0054] Specifically, the signal processing device 10 calculates a function X representing a waveform before modulation of a partial signal belonging to the m-th group. m (t), and the function representing the waveform after modulation of the partial signal is Y m If (t), the following modulation is performed. Y m (t) = (1 + R × A m (t))·X m (t)

[0055] Here, R represents the modulation depth (the magnitude of the change in amplitude caused by modulation), m is an integer between 1 and M, and A m (t) represents the modulation function used for the partial signal belonging to the m-th group. A1(t), ,A M The frequencies of (t) are the same, but the phases are different. m (t) is delayed in phase by 2π(m-1) / M[rad] compared to A1(t), and A MA2(t) has a phase lead of 2π(Mm) / M [rad] compared to A1(t). In other words, when M=2, A2(t) lags A1(t) by π [rad] (180 degrees), when M=3, A2(t) and A3(t) lag A1(t) by 2π / 3 [rad] (120 degrees) and 4π / 3 [rad] (240 degrees), respectively, and when M=4, A2(t), A3(t) and A4(t) lag A1(t) by π / 2 [rad], π [rad] and 3π / 2 [rad], respectively.

[0056] The waveform of each modulation function is approximately equal to a shape obtained by repeating an arbitrary unit waveform at a period corresponding to a predetermined frequency. The shape of the unit waveform is arbitrary, but may be any of the following, or a combination (combination) of two or more of them. Trapezoidal wave ·Square wave ·Triangle wave ·Sine wave Sawtooth Wave Reverse sawtooth wave

[0057] The waveform of the envelope of a modulated partial signal is determined by the waveform of the modulation function used to modulate the signal. For example, the waveform of the envelope of a partial signal modulated by a modulation function corresponding to a trapezoidal waveform is a trapezoidal waveform. On the other hand, the waveform of the envelope of a partial signal modulated by a modulation function corresponding to a rectangular waveform is a rectangular waveform.

[0058] As a result, as shown in FIG. 5, an amplitude change (volume strength) corresponding to a predetermined frequency (approximately 20 Hz) is added to the envelope of the partial signal belonging to the first group, and an amplitude change (volume strength) corresponding to a predetermined frequency (approximately 20 Hz) is also added to the envelope of the partial signal belonging to the second group. However, the envelope of the partial signal belonging to the second group is delayed in phase by a half period from the envelope of the partial signal belonging to the first group. In other words, the envelope of the partial signal belonging to the second group has an amplitude change corresponding to a predetermined frequency and having a different phase from the envelope of the partial signal belonging to the first group. When focusing on each partial signal included in the output sound signal, a portion where the volume of the partial signal belonging to the first group becomes stronger and a portion where the volume of the partial signal belonging to the second group becomes stronger appear alternately at approximately equal intervals every 1 / 40th of a second. Similarly, when focusing on each partial signal included in the output sound signal, a portion where the volume of the partial signal belonging to the first group becomes weaker and a portion where the volume of the partial signal belonging to the second group becomes weaker appear alternately at approximately equal intervals every 1 / 40th of a second.

[0059] After step S112, the signal processing device 10 generates an output acoustic signal (S113). Specifically, the signal processing device 10 generates an output acoustic signal based on the multiple partial signals modulated in step S112. When the multiple modulated partial signals match the output format of the audio output device 30 (for example, when the multiple modulated partial signals correspond to multi-channel audio signals associated with the respective speakers constituting a surround system as the audio output device 30), step S113 can be omitted. In this case, the multiple modulated partial signals are treated as output audio signals. On the other hand, when the multiple modulated partial signals do not match the output format of the audio output device 30, the signal processing device 10 converts the multiple modulated partial signals into an output audio signal. Specifically, the signal processing device 10 synthesizes two or more audio signals among the multiple modulated partial signals, or extracts or separates an audio signal from at least one of the multiple modulated partial signals. The method of synthesizing the audio signals is not limited, and may include, for example, signal summation processing, HRTF (Head Related Transfer Function) convolution processing, transfer function convolution processing that imparts position information of a sound source, or summation processing after performing these convolution processing. In step S113, the signal processing device 10 may further perform at least one of amplification, volume adjustment, or D / A conversion of the output acoustic signal.

[0060] After step S113, the signal processing device 10 executes transmission of an output acoustic signal (S114). Specifically, the signal processing device 10 sends the output acoustic signal generated in step S113 to the acoustic output device 30. The acoustic output device 30 generates a sound corresponding to the output acoustic signal. After step S114, the signal processing device 10 ends the acoustic signal processing in FIG. The signal processing device 10 may perform the process of FIG. 4 all at once on an input audio signal having a certain playback period (e.g., one piece of music content), or may repeatedly perform the process of FIG. 4 for each predetermined playback section of the input audio signal (e.g., every 100 ms). Alternatively, the signal processing device 10 may continuously perform modulation processing on the input audio signal, such as modulation by analog signal processing, and output a modulated audio signal. The process shown in FIG. 4 may end in response to a specific end condition (e.g., a certain amount of time has passed, a user operation has been performed, or the output history of the modulated sound has reached a predetermined state).

[0061] (5) Experimental results An experiment conducted to verify the effect of the technology of the present disclosure will be described below. Fig. 8 is a graph showing the results of the experiment.

[0062] In this experiment, subjects with normal hearing listened to output sounds based on the audio signals generated by the technology of the present disclosure, and the degree of gamma wave synchronization in the subjects' brains was evaluated. For comparison, the degree of gamma wave synchronization was also evaluated when subjects listened to output sounds based on audio signals generated by changing the frequency of the modulation function used for amplitude modulation. The degree of gamma wave synchronization was measured using electrodes attached to the subjects' heads. Earphones inserted into the subjects' ears were used as the audio output device that generates output sounds in response to audio signals.

[0063] Graphs g41 to g43 in FIG. 8 show the synchronization index (PLI) of the electroencephalogram waveform obtained from an active electrode placed on the vertex (Cz) of the subject when the subject is made to listen to the output sound. Graph g41 shows the PLI when the subject is made to listen to a sound based on an audio signal obtained by amplitude-modulating two partial signals included in a sample music signal using a 20 Hz modulation function (phases differing from each other by 180 degrees) as the output sound (hereinafter referred to as a "20 Hz split modulated sound"). Graph g42 shows the PLI when the subject is made to listen to a sound based on an audio signal obtained by amplitude-modulating two partial signals included in the sample music signal using a 40 Hz modulation function (phases differing from each other by 180 degrees) as the output sound (hereinafter referred to as a "40 Hz split modulated sound"). The first and second partial signals used to generate these split modulated sounds were generated by dividing the sample music signal every 1 / 3 octave. Graph g43 represents the PLI when the subject is made to listen to the sound based on the above sample music signal (hereinafter referred to as the "original sound") as the output sound.

[0064] The 20Hz split modulated sound had a better PLI than the original sound, and the gamma wave synchronization effect was confirmed. On the other hand, the 40Hz split modulated sound did not have an improved PLI compared to the original sound, and the gamma wave synchronization effect was not confirmed. This shows that a unique effect of promoting gamma wave synchronization can be obtained by performing amplitude modulation using a modulation function having a frequency that is approximately 1 / M of the frequency corresponding to gamma waves (for example, a frequency of 35 Hz or more and 45 Hz or less) on the partial signal divided into M pieces. In addition, compared to the pulse sound described in Non-Patent Document 1 and the sound obtained by modulating the entire original sound at a specific frequency, the split modulated sound suppresses the change in the strength of the volume of the entire output sound, so the discomfort felt by the listener is suppressed. This result shows the possibility that the acoustic system 1 can output a sound stimulus that is not felt to be unpleasant by the user even when listening to it on a daily basis, and improve the cognitive function of the user.

[0065] (6) Summary As described above, the signal processing device 10 of the present embodiment receives an input sound signal, and acquires a first sound signal having an amplitude change corresponding to a predetermined frequency by amplitude-modulating a first partial signal included in the input sound signal. The signal processing device 10 also acquires a second sound signal having an amplitude change corresponding to the predetermined frequency and having a phase different from that of the first sound signal by amplitude-modulating a second partial signal included in the input sound signal, and outputs an output sound signal based on the acquired first sound signal and second sound signal. As a result, when focusing on each partial signal included in the output sound signal, the volume of each of the multiple modulated sound signals having different phases appears alternately at a number of times (for example, a total of 40 times) according to the predetermined frequency and the number of divisions of the partial signal per second. When a user listens to a sound corresponding to such an output sound signal, gamma waves are induced or synchronized in the user's brain, or both are caused. As a result, an effect of improving the user's cognitive function (for example, treatment or prevention of dementia) can be expected. On the other hand, since the multiple modulated audio signals with different phases have different locations where the volume increases and decreases in the output audio signal, the difference between the maximum volume and minimum volume of the sound based on the output audio signal is reduced compared to when these signals are the same, thereby suppressing deterioration of the user's audio experience.

[0066] The sound corresponding to the first partial signal and the sound corresponding to the second partial signal may have different frequency bands. As a result, when focusing on the partial signals of each frequency band contained in the output sound signal, the volume of the frequency bands corresponding to each partial signal alternates between strong and weak sounds per second, the number of times corresponding to the predetermined frequency and the number of divisions of the partial signal.

[0067] The sound corresponding to the first partial signal may include a sound in a first frequency band and a sound in a third frequency band, and the sound corresponding to the second partial signal may include a sound in a second frequency band and a sound in a fourth frequency band. Here, the first frequency band is lower than the second frequency band, the second frequency band is lower than the third frequency band, and the third frequency band is lower than the fourth frequency band. This makes it possible to suppress bias in the frequency bands of the acoustic signals included in each partial signal.

[0068] The sound corresponding to the first partial signal and the sound corresponding to the second partial signal may differ in at least one of the sound source type, sound source direction, and recording position. This makes it possible to induce or synchronize gamma waves in the user's brain while suppressing deterioration of the user's acoustic experience by gently changing the volume of the sound corresponding to each of the sound source type, sound source direction, and recording position in the output acoustic signal.

[0069] The predetermined frequency may be about 20 Hz. The phase of the change in amplitude of the first acoustic signal may differ from the phase of the change in amplitude of the second acoustic signal by about 180 degrees. As a result, when focusing on each partial signal included in the output acoustic signal, the first acoustic signal and the second acoustic signal alternate in strength and weakness at substantially equal intervals, a total of about 40 times per second.

[0070] The signal processing device 10 may obtain a third acoustic signal having an amplitude change corresponding to the predetermined frequency and having a phase different from that of the first acoustic signal and the second acoustic signal by amplitude modulating a third partial signal included in the input acoustic signal. The signal processing device 10 may output an output acoustic signal based on the obtained first acoustic signal, second acoustic signal, and third acoustic signal. As a result, when focusing on each partial signal included in the output acoustic signal, the volume of each of three or more modulated acoustic signals having different phases appears alternately strong and weak a number of times (for example, a total of 40 times) according to the predetermined frequency and the number of divisions of the partial signal per second.

[0071] The predetermined frequency may be about 13 Hz. The phase of the amplitude change of the first acoustic signal may lead about 120 degrees from the phase of the amplitude change of the second acoustic signal. The phase of the amplitude change of the second acoustic signal may lead about 120 degrees from the phase of the amplitude change of the third acoustic signal. As a result, when focusing on partial signals of each frequency band contained in the output acoustic signal, the first acoustic signal, the second acoustic signal, and the third acoustic signal alternate in strong and weak volume at substantially equal intervals a total of about 40 times per second.

[0072] The envelope of the amplitude waveform of the first acoustic signal and the envelope of the amplitude waveform of the second acoustic signal may be a rectangular wave, a triangular wave, or a trapezoidal wave. This makes the envelope of the output acoustic signal obtained by combining the acoustic signals substantially flat (i.e., the overall volume change of the output acoustic signal is suppressed), so that gamma waves can be induced or synchronized in the user's brain while suppressing deterioration of the user's acoustic experience.

[0073] The input audio signal may be an audio signal that includes music content, which makes it easier for a user to engage with listening to sounds based on the output audio signal.

[0074] The acoustic system 1 of this embodiment corresponds to a cognitive function improvement system for improving the cognitive function of a user. The acoustic system 1 includes the signal processing device 10, and causes at least one of induction and synchronization of gamma waves in the user's brain by playing a sound corresponding to an output acoustic signal output by the signal processing device 10 to the user. This makes it possible to improve the cognitive function of the user.

[0075] (7) Other modifications The storage device 11 may be connected to the signal processing device 10 via a network NW. The display 21 may be integrated with the signal processing device 10.

[0076] In the above description, the frequency corresponding to gamma waves is mainly assumed to be 35 Hz or more and 45 Hz or less. However, the present invention is not limited to this, and any numerical range that affects the induction or synchronization of gamma waves in the brain of a listener can be assumed as the frequency corresponding to gamma waves. For example, the frequency corresponding to gamma waves may be assumed to be 25 Hz or more and 140 Hz or less. For example, the frequency may change over time, and a frequency less than 35 Hz or a frequency higher than 45 Hz may be temporarily allowed as the frequency.

[0077] In the above description, the output acoustic signal generated by the signal processing device 10 is output to the acoustic output device 30 that generates a sound corresponding to the output acoustic signal and lets the user hear it. However, the output destination of the output acoustic signal by the signal processing device 10 is not limited to this. For example, the signal processing device 10 may output the output acoustic signal to an external storage device or information processing device via a communication network or by broadcasting. At this time, the signal processing device 10 may output an input acoustic signal that has not been modulated to the external device together with the output acoustic signal generated by the modulation process. This allows the external device to arbitrarily select and play either the acoustic signal that has not been modulated or the acoustic signal that has been modulated. Furthermore, the signal processing device 10 may output information indicating the content of the modulation process to an external device together with the output acoustic signal. The information indicating the content of the modulation process includes, for example, any of the following: -Information indicating the sound source corresponding to the modulated target signal -Information indicating the channel that corresponds to the modulated target signal - Information that indicates the characteristics of the modulated signal Information showing modulation function -Information showing modulation depth -Volume information This allows the external device to change the method of reproducing the audio signal depending on the content of the modulation process. Furthermore, when the signal processing device 10 acquires additional information (for example, an ID3 tag in an MP3 file) together with the input audio signal, the signal processing device 10 may modify the additional information and output it to an external device together with the output audio signal.

[0078] In the present embodiment, an example has been described in which modulation functions that differ only in phase are applied to different partial signals. However, it is also possible to apply modulation functions (which may include amplitude or modulation depth) that differ in waveform in addition to phase (but have the same frequency) to different partial signals.

[0079] In the above description, an example has been given in which an input sound signal is divided into a plurality of frequency bands (subbands). Here, the division may be performed on a logarithmic scale or a linear scale. Dividing on a logarithmic scale is expected to have the effect of facilitating auditory sound quality control. On the other hand, dividing on a linear scale suppresses the variation in energy between partial signals. In addition, the number of subbands may be two (i.e., a low frequency side and a high frequency side). It is expected that the discomfort level will be suppressed as the width of the subband becomes narrower (i.e., the frequency band is divided finer).

[0080] In the present embodiment, an example has been shown in which a plurality of partial signals included in an input sound signal are amplitude-modulated using modulation functions with different phases. Here, the input sound signal may include sound signals obtained from a plurality of completely different sound sources. In this case, the sound signals corresponding to each sound source may be treated as partial signals.

[0081] In the above description, the frequency band is divided into three or more subbands, and the phases of the modulation functions are assigned in ascending or descending order to each subband arranged in ascending or descending order of frequency. However, the assignment of the phases of the modulation functions to each subband may be a more complicated pattern or may be determined randomly. Furthermore, the assignment of phases to each partial signal may be changed (hopped) over time. As a result, the phases of the modulation functions assigned to a specific subband or a partial signal corresponding to a specific sound source are not fixed, so that even if an unintended change in tone occurs due to modulation, the change in tone is less likely to be recognized by the user.

[0082] The modulation depth of the modulation function may be controlled for each section or each modulation function, for example. The lower the modulation depth, the less the listener's discomfort, but the less the gamma wave induction effect or synchronization effect tends to decrease. For example, by lowering the modulation depth of the modulation function in a specific section compared to other sections, or by lowering the modulation depth of the modulation function used to modulate a partial signal corresponding to a specific sound source (e.g., a partial signal corresponding to vocals or a solo instrument) compared to other sound sources, it is possible to effectively reduce the listener's discomfort while suppressing the decrease in the gamma wave induction effect or synchronization effect.

[0083] The modulation process of this embodiment (i.e., a process of performing amplitude modulation on multiple partial signals included in an input audio signal using modulation functions with different phases) can be used in combination with other modulation processes (e.g., a process of performing amplitude modulation on the entire input audio signal or on some of the multiple partial signals included in an input audio signal using a single modulation function). For example, when a section containing only a specific sound source (e.g., accompaniment, vocals, etc.) or a section in which the components of a specific sound source are dominant is detected in the input audio signal, the other modulation processes may be used instead of the modulation process of this embodiment. Alternatively, when the input audio signal corresponds to a sound source for which emphasis should be placed on naturalness (e.g., a sound source for which sound source separation processing with a certain level of accuracy is difficult), the modulation process of this embodiment may be used instead of the other modulation processes.

[0084] In the above description, the signal processing device 10 mainly generates an output acoustic signal by modulating all partial signals included in the input acoustic signal with the same frequency. However, the present invention is not limited to this, and the output acoustic signal may include other partial signals that are not modulated with the same frequency as some partial signals. For example, when the input acoustic signal includes a first partial signal, a second partial signal, and a third partial signal, the signal processing device 10 may modulate the first partial signal and the second partial signal with the same frequency but different phases, and modulate the third partial signal with a different frequency. Alternatively, the third partial signal may not be modulated. Then, the signal processing device 10 may output an output acoustic signal based on the first partial signal, the second partial signal, and the third partial signal.

[0085] In the above-mentioned embodiment, the case where the acoustic system including the signal processing device 10 is used as a cognitive function improvement system for improving cognitive function (for example, treatment or prevention of dementia) has been mainly described. However, the use of the signal processing device 10 is not limited to this. Non-Patent Document 1 discloses that when a 40 Hz sound stimulus induces gamma waves in the brain, amyloid β is reduced and cognitive function is improved. That is, by making the user listen to a sound corresponding to the output acoustic signal output by the signal processing device 10, amyloid β in the user's brain is reduced and deposition is suppressed, and it is expected to be useful for preventing or treating diseases caused by an increase or deposition of amyloid β. An example of a disease caused by the deposition of amyloid β is cerebral amyloid angiopathy (CAA). CAA is a disease in which amyloid β protein is deposited on the walls of small blood vessels in the brain, making the blood vessel walls fragile and making cerebral hemorrhage more likely to occur. As with dementia, there is no treatment for CAA itself, so the technology described in the above-mentioned embodiment can be an innovative treatment method. In other words, an audio system 1 comprising a signal processing device 10 and an audio output device 30 that plays a sound corresponding to an output audio signal output by the signal processing device 10 to a user can also be used as a medical system for treating or preventing cerebral amyloid angiopathy.

[0086] (8) Additional Notes The matters described in the embodiment and the modified examples are supplemented below.

[0087] (Appendix 1) A means for receiving an input sound signal (S110); A means (S112) for obtaining a first acoustic signal having an amplitude change corresponding to a predetermined frequency by amplitude modulating a first partial signal included in an input acoustic signal; A means (S112) for acquiring a second acoustic signal having an amplitude change corresponding to a predetermined frequency and out of phase with the first acoustic signal by amplitude modulating a second partial signal included in the input acoustic signal; and a means (S114) for outputting an output acoustic signal based on the acquired first acoustic signal and second acoustic signal. A signal processing device (10).

[0088] (Appendix 2) The sound corresponding to the first partial signal and the sound corresponding to the second partial signal have different frequency bands. 2. A signal processing device as claimed in claim 1.

[0089] (Appendix 3) the sounds corresponding to the first partial signal include sounds in a first frequency band and sounds in a third frequency band; the sounds corresponding to the second partial signal include sounds in the second frequency band and sounds in the fourth frequency band; The first frequency band is lower than the second frequency band, The second frequency band is lower than the third frequency band, The third frequency band is lower than the fourth frequency band, 3. A signal processing device as claimed in claim 2.

[0090] (Appendix 4) The sound corresponding to the first partial signal and the sound corresponding to the second partial signal are different in at least one of the sound source type, the sound source direction, and the recording position. 4. A signal processing device according to any one of claims 1 to 3.

[0091] (Appendix 5) The predetermined frequency is about 20 Hz, The phase of the change in amplitude of the first acoustic signal and the phase of the change in amplitude of the second acoustic signal are different by approximately 180 degrees. 5. A signal processing device according to claim 1,

[0092] (Appendix 6) a means for acquiring a third acoustic signal having an amplitude change corresponding to a predetermined frequency and having a phase different from that of the first acoustic signal and the second acoustic signal by amplitude modulating a third partial signal included in the input acoustic signal, the output means outputs an output acoustic signal based on the acquired first acoustic signal, second acoustic signal, and third acoustic signal. 5. A signal processing device according to claim 1,

[0093] (Appendix 7) The predetermined frequency is about 13 Hz, the phase of the amplitude change of the first acoustic signal leads the phase of the amplitude change of the second acoustic signal by approximately 120 degrees; the phase of the change in amplitude of the second acoustic signal leads the phase of the change in amplitude of the third acoustic signal by approximately 120 degrees; 7. The signal processing device according to claim 6.

[0094] (Appendix 8) The envelope of the amplitude waveform of the first acoustic signal and the envelope of the amplitude waveform of the second acoustic signal are rectangular, triangular, or trapezoidal. 8. A signal processing device according to any one of claims 1 to 7.

[0095] (Appendix 9) the input audio signal is an audio signal containing music content; 9. A signal processing device according to any one of claims 1 to 8.

[0096] (Appendix 10) A cognitive function improvement system (1) for improving a user's cognitive function, A signal processing device according to any one of Supplementary Note 1 to Supplementary Note 9; and a means (30) for inducing and / or synchronizing gamma waves in the user's brain by playing a sound corresponding to the output acoustic signal output by the signal processing device to the user. Cognitive function improvement system.

[0097] (Appendix 11) A computer (10), A step of receiving an input acoustic signal (S110); A step (S112) of acquiring a first acoustic signal having an amplitude change corresponding to a predetermined frequency by amplitude modulating a first partial signal included in the input acoustic signal; A step (S112) of acquiring a second acoustic signal having an amplitude change corresponding to a predetermined frequency and out of phase with the first acoustic signal by amplitude modulating a second partial signal included in the input acoustic signal; outputting an output acoustic signal based on the acquired first acoustic signal and second acoustic signal (S114); A method for performing.

[0098] (Appendix 12) A program for causing a computer to realize each of the means of the signal processing device according to any one of Supplementary Note 1 to Supplementary Note 9.

[0099] Although the embodiment of the present invention has been described in detail above, the scope of the present invention is not limited to the above embodiment. Furthermore, the above embodiment can be improved or modified in various ways without departing from the spirit of the present invention. Furthermore, the above embodiment and the modified examples can be combined. [Explanation of symbols]

[0100] 1: Sound system 10: Signal processing device 11:Storage device 12: Processor 13: Input / Output Interface 14: Communication interface 21: Display 30: Sound output device 50: Sound source device

Claims

1. means for receiving an input audio signal; a means for obtaining a first acoustic signal having an amplitude change corresponding to a predetermined frequency by amplitude modulating a first partial signal included in the input acoustic signal; a means for obtaining a second acoustic signal having an amplitude change corresponding to the predetermined frequency and out of phase with the first acoustic signal by amplitude modulating a second partial signal included in the input acoustic signal; and a means for outputting an output acoustic signal based on the acquired first acoustic signal and the acquired second acoustic signal. Signal processing device.

2. The sound corresponding to the first partial signal and the sound corresponding to the second partial signal have different frequency bands. The signal processing device according to claim 1 .

3. the sounds corresponding to the first partial signal include sounds in a first frequency band and sounds in a third frequency band; the sounds corresponding to the second partial signal include sounds in a second frequency band and sounds in a fourth frequency band; the first frequency band is lower than the second frequency band; the second frequency band is lower than the third frequency band; the third frequency band is lower than the fourth frequency band; The signal processing device according to claim 2 .

4. The sound corresponding to the first partial signal and the sound corresponding to the second partial signal are different in at least one of a sound source type, a sound source direction, and a recording position. The signal processing device according to claim 1 .

5. the predetermined frequency is about 20 Hz; the phase of the change in amplitude of the first acoustic signal differs from the phase of the change in amplitude of the second acoustic signal by approximately 180 degrees; The signal processing device according to claim 1 .

6. a means for acquiring a third acoustic signal having an amplitude change corresponding to the predetermined frequency and having a phase different from that of the first acoustic signal and the second acoustic signal by amplitude modulating a third partial signal included in the input acoustic signal, the output means outputs the output acoustic signal based on the acquired first acoustic signal, the second acoustic signal, and the third acoustic signal. The signal processing device according to claim 1 .

7. the predetermined frequency is approximately 13 Hz; the phase of the change in amplitude of the first acoustic signal leads the phase of the change in amplitude of the second acoustic signal by approximately 120 degrees; the phase of the change in amplitude of the second acoustic signal leads the phase of the change in amplitude of the third acoustic signal by approximately 120 degrees; The signal processing device according to claim 6.

8. The envelope of the amplitude waveform of the first acoustic signal and the envelope of the amplitude waveform of the second acoustic signal have a rectangular wave shape, a triangular wave shape, or a trapezoidal wave shape. The signal processing device according to claim 1 .

9. the input audio signal is an audio signal including music content; The signal processing device according to claim 1 .

10. A cognitive function improvement system for improving a user's cognitive function, A signal processing device according to any one of claims 1 to 9, and a means for inducing and / or synchronizing gamma waves in the user's brain by playing a sound corresponding to the output acoustic signal output by the signal processing device to the user. Cognitive function improvement system.

11. The computer accepting an input acoustic signal; obtaining a first acoustic signal having an amplitude change corresponding to a predetermined frequency by amplitude modulating a first partial signal included in the input acoustic signal; obtaining a second acoustic signal having an amplitude change corresponding to the predetermined frequency and out of phase with the first acoustic signal by amplitude modulating a second partial signal included in the input acoustic signal; outputting an output acoustic signal based on the acquired first acoustic signal and the acquired second acoustic signal; A method for performing.

12. A program for causing a computer to realize each of the means of the signal processing device according to any one of claims 1 to 9.

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