Signal processing device, system, signal generation method, and program

Abstract

To provide a signal processor, a system for improving cognitive function, a signal processing method, and a program for changing amplitude of acoustic signals while suppressing discomfort to a listener.SOLUTION: In an acoustic system comprising a signal processor, an acoustic output device, and a sound source device, acoustic signal processing flow by the signal processor includes: accepting an input acoustic signal; generating an output acoustic signal having an amplitude change corresponding to the frequency of a gamma wave and having an asymmetric rise and fall of an envelope of amplitude waveform, by subjecting the accepted input acoustic signal to amplitude modulation; and outputting the generated output acoustic signal.SELECTED DRAWING: Figure 8

Description

Technical Field

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

[0002] There is a research report stating that causing an organism to perceive pulsed sound stimulation at a frequency of approximately 40 times per second to induce gamma waves in the organism's brain is effective in improving the organism's cognitive function (see Non-Patent Document 1). Gamma waves refer to neural oscillations, obtained by capturing periodic neural activity in the cerebral cortex via electrophysiological methods such as electroencephalography and magnetoencephalography, whose frequencies fall within the gamma band (25 to 140 Hz).

[0003] Patent Document 1 discloses adjusting sound volume by increasing or decreasing the amplitude of sound waves or a soundtrack to generate rhythmic stimulation corresponding to a stimulation frequency that induces brain wave entrainment. Prior Art Literature Patent Literature

[0004] Patent Document 1 Japanese National Publication of International Patent Application 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 Invention Problem to be Solved by the Invention

[0006] However, there has been insufficient study on what waveform is desirable when increasing or decreasing the amplitude of an acoustic signal. Even acoustic signals with the same frequency periodicity may differ in their cognitive function improvement effect and the level of discomfort they cause to the listener depending on the characteristics of their amplitude waveform.

[0007] The purpose of this disclosure is to change the amplitude of an acoustic signal while suppressing discomfort to the listener. [Means for solving the problem]

[0008] A signal processing device according to one aspect of the present disclosure includes means for receiving an input acoustic signal, means for generating an output acoustic signal having an amplitude change corresponding to the frequency of a gamma wave and having asymmetrical rising and falling edges of the envelope of the amplitude waveform by amplitude modulation of the received input acoustic signal, and means for outputting the generated output acoustic signal. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of the acoustic system of this embodiment. [Figure 2] This is a block diagram showing the configuration of the signal processing device of this embodiment. [Figure 3] This is an explanatory diagram of one aspect of this embodiment. [Figure 4] This figure shows a first example of the amplitude waveform of the output acoustic signal. [Figure 5] This figure shows a second example of the amplitude waveform of the output acoustic signal. [Figure 6] This figure shows a third example of the amplitude waveform of the output acoustic signal. [Figure 7] This figure shows the results of the experiment. [Figure 8] This diagram shows the overall flow of acoustic signal processing by the signal processing device of this embodiment. [Figure 9] This figure shows a list of the sound stimuli used in the experiment. [Figure 10]This figure shows the experimental results of brainwave induction using auditory stimuli. [Figure 11] This figure shows the correlation between psychological experiments and electroencephalogram (EEG) measurements. [Modes for carrying out the invention]

[0010] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In the drawings used to illustrate the embodiment, the same reference numerals are generally used for identical components, and repeated descriptions thereof will be omitted.

[0011] (1) Configuration of the sound system The configuration of the sound system will now be described. Figure 1 is a block diagram showing the configuration of the sound system in this embodiment.

[0012] As shown in Figure 1, the acoustic system 1 comprises a signal processing device 10, an acoustic output device 30, and a sound source device 50.

[0013] The signal processing device 10 and the sound source device 50 are connected to each other via a predetermined interface capable of transmitting acoustic signals. The interface may be, for example, SPDIF (Sony Philips Digital Interface), HDMI (High-Definition Multimedia Interface), a pin connector (RCA pin), or an audio interface for headphones. The interface may also be a wireless interface using Bluetooth (registered trademark). The signal processing device 10 and the sound output device 30 are similarly connected to each other via a predetermined interface. The acoustic signal in this embodiment includes either an analog signal or a digital signal, or both.

[0014] The signal processing device 10 performs acoustic signal processing on an input acoustic signal acquired from the sound source device 50. The acoustic signal processing performed by the signal processing device 10 includes at least acoustic signal modulation processing (details will be described later). Further, the acoustic signal processing performed by the signal processing device 10 may include conversion processing (e.g., separation, extraction, or synthesis) of the acoustic signal. Furthermore, the acoustic signal processing performed by the signal processing device 10 may further include, for example, amplification processing of an acoustic signal similar to that performed by an AV amplifier. The signal processing device 10 transmits an output acoustic signal generated by the acoustic signal processing to the acoustic output device 30. The signal processing device 10 is an example of an information processing device.

[0015] The acoustic output device 30 generates sound in accordance with the output acoustic signal acquired from the signal processing device 10. The acoustic output device 30 is, for example, a loudspeaker (may include an amplifier built-in speaker (powered speaker)), headphones, or earphones. The acoustic output device 30 can also be configured as a single device together with the signal processing device 10. Specifically, the signal processing device 10 and the acoustic output device 30 can be mounted on a TV, a radio, a music player, an AV amplifier, a speaker, headphones, earphones, a smartphone, or a PC. The signal processing device 10 and the acoustic output device 30 constitute a cognitive function improvement system.

[0016] The sound source device 50 transmits the input acoustic 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, an electronic musical instrument, a telephone, a game console, a game machine, or a device that carries an acoustic signal via broadcasting or information communication.

[0017] (1-1) Configuration of the Signal Processing Device The configuration of the signal processing device will be described. Fig. 2 is a block diagram showing the configuration of the signal processing device of the present embodiment.

[0018] As shown in Fig. 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.

[0019] The storage device 11 is configured to store programs and data. The storage device 11 is, for example, a combination of ROM (Read Only Memory), RAM (Random Access Memory), and storage (e.g., flash memory or hard disk). The programs and data may be provided via a network or by being recorded on a computer-readable recording medium.

[0020] The program includes, for example, the following: • OS (Operating System) programs • Programs for applications that perform information processing.

[0021] The data includes, for example, the following: • Databases referenced in information processing • Data obtained by performing information processing (i.e., the results of performing information processing)

[0022] 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 memory device 11. At least a portion 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 Array) ·DSP(digital signal processor)

[0023] The input / output interface 13 is configured to receive 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 devices include, for example, a sound source device 50, physical buttons, a keyboard, a pointing device, a touch panel, or a combination thereof. The output devices are, for example, a display 21, an audio output device 30, or a combination thereof.

[0024] Furthermore, the input / output interface 13 may include signal processing hardware such as an A / D converter, a D / A converter, an amplifier, a mixer, and a filter.

[0025] The communication interface 14 is configured to control communication between the signal processing device 10 and an external device (for example, an acoustic output device 30 or a sound source device 50).

[0026] The display 21 is configured to display images (still images or moving images). The display 21 is, for example, a liquid crystal display or an organic EL display.

[0027] (2) One embodiment One aspect of this embodiment will be described. Figure 3 is an explanatory diagram of one aspect of this embodiment.

[0028] (2-1) Overview of the Embodiment As shown in Figure 3, the signal processing device 10 acquires an input acoustic signal from the sound source device 50. The signal processing device 10 generates an output acoustic signal by modulating the input acoustic signal. The modulation is amplitude modulation using a modulation function with a frequency corresponding to gamma waves (for example, a frequency between 35 Hz and 45 Hz). As a result, the acoustic signal is given a change in amplitude (volume intensity) corresponding to the above frequency. If different modulation functions are applied to the same input acoustic signal, the amplitude waveform of the output acoustic signal will be different. Examples of amplitude waveforms will be described later.

[0029] The signal processing device 10 sends the output acoustic signal to the acoustic output device 30. The acoustic output device 30 generates an output sound corresponding to the output acoustic signal.

[0030] User US1 (an example of a "hearer") listens to the output sound emitted from the acoustic output device 30. User US1 may be, for example, a dementia patient, a person at risk of dementia, or a healthy person who hopes to prevent dementia. As mentioned above, the output acoustic signal is based on an output acoustic signal modulated using a modulation function having a periodicity of 35 Hz to 45 Hz. Therefore, when User US1 listens to the sound emitted from the acoustic output device 30, gamma waves are induced in User US1's brain. This is expected to improve User US1's cognitive function (for example, in the treatment or prevention of dementia).

[0031] (2-2) First example of amplitude waveform Figure 4 shows a first example of the amplitude waveform of the output acoustic signal. If A(t) is the modulation function used to modulate the input acoustic signal, X(t) is the function representing the waveform of the input acoustic signal before modulation, and Y(t) is the function representing the waveform of the output acoustic signal after modulation, then Y(t) = A(t)·X(t) This is the result. In the first example, the modulation function has an inverse sawtooth waveform at 40 Hz. The input acoustic signal is a homogeneous sound signal with a constant frequency higher than 40 Hz and constant sound pressure. As a result, the envelope of the amplitude waveform of the output acoustic signal takes on a shape that follows an inverse sawtooth wave. Specifically, as shown in Figure 4, the amplitude waveform of the output acoustic signal has amplitude changes corresponding to the frequency of the gamma wave, and the rising portion C and falling portion B of the envelope A of the amplitude waveform are asymmetric (i.e., the rising time length and the falling time length are different). In the first example, the rising edge of envelope A of the amplitude waveform of the output acoustic signal is steeper than the falling edge. In other words, the time required for the rising edge is shorter than the time required for the falling edge. The amplitude value of envelope A rises sharply to its maximum amplitude and then gradually decreases over time. That is, envelope A has an inverse sawtooth wave pattern.

[0032] (2-3) Second example of amplitude waveform A second example of the amplitude waveform of the output acoustic signal will be described. Figure 5 shows a second example of the amplitude waveform of the output acoustic signal.

[0033] In the second example, the modulation function has a sawtooth waveform at 40 Hz. The input acoustic signal is a homogeneous sound signal with a constant frequency higher than 40 Hz and constant sound pressure. As a result, the envelope of the amplitude waveform of the output acoustic signal takes on a shape that follows a sawtooth wave. Specifically, as shown in Figure 5, the falling edge of envelope A of the amplitude waveform of the output acoustic signal in the second example is steeper than the rising edge. In other words, the time required for the falling edge is shorter than the time required for the rising edge. The amplitude value of envelope A gradually increases over time to its maximum amplitude, and then drops sharply. That is, envelope A has a sawtooth wave shape.

[0034] (2-4) Third example of amplitude waveform A third example of the amplitude waveform of the output acoustic signal will be described. Figure 6 is a diagram showing the third example of the amplitude waveform of the output acoustic signal. In the third example, the modulation function has a sinusoidal waveform of 40 Hz. The input acoustic signal is a homogeneous sound signal with a constant frequency higher than 40 Hz and constant sound pressure. As a result, the envelope of the amplitude waveform of the output acoustic signal has a shape that follows a sinusoidal wave. Specifically, as shown in Figure 6, in the third example, both the rising and falling edges of the envelope A of the amplitude waveform of the output acoustic signal are smooth. In other words, envelope A is sinusoidal. In the first to third examples above, the modulation function was assumed to have a periodicity of 40 Hz, but the frequency of the modulation function is not limited to this, and may be, for example, between 35 Hz and 45 Hz. Also, in the first to third examples above, the absolute value of the amplitude of envelope A was assumed to be periodically zero, but this is not limited to this, and a modulation function may be used such that the minimum absolute value of the amplitude of envelope A is greater than zero (for example, half or a quarter of the maximum absolute value).

[0035] In the examples shown in Figures 4 to 6, the sound pressure and frequency of the input acoustic signal are assumed to be constant, but the sound pressure and frequency of the input acoustic signal may change. For example, the input acoustic signal may be a signal representing music, speech, ambient sound, electronic sound, or noise. In this case, although the envelope of the amplitude waveform of the output acoustic signal will have a shape that is strictly different from the waveform representing the modulation function, the general shape of the envelope will be similar to that of the waveform representing the modulation function (e.g., inverse sawtooth wave, sawtooth wave, or sine wave), and it will be possible to provide the listener with the same auditory stimulation as when the sound pressure and frequency of the input acoustic signal are constant.

[0036] (2-5) Experimental Results (2-5-1) Overview of the experiment This section describes the experiments conducted to verify the effectiveness of the technology disclosed herein. In this experiment, 18 male and 8 female subjects were exposed to output sounds based on acoustic signals modulated using a 40Hz modulation function, and their psychological responses and the degree of gamma wave induction in the brain were evaluated. For comparison, the psychological responses and the degree of gamma wave induction when exposed to output sounds based on acoustic signals with a 40Hz pulsed waveform were also evaluated. Psychological responses were evaluated based on the subjective opinions of the subjects using a questionnaire (7-point scale). The degree of gamma wave induction was measured using multiple electrodes attached to the subjects' heads. Headphones worn on the subjects' heads were used as the acoustic output device 30 that generates output sounds in response to the modulated acoustic signal.

[0037] In this experiment, we conducted experiments A through C in the following order. Experiment A: In this experiment, participants report their level of discomfort when listening to multiple types of output sounds, each corresponding to a different modulation function and input acoustic signal. Experiment B: An experiment to measure the brainwaves of subjects while they listen to multiple types of output sounds corresponding to different modulation functions and input acoustic signals. Experiment C: An experiment measuring the brainwaves of subjects while they listen to multiple types of output sounds corresponding to different modulation functions and input acoustic signals (the length of the sounds differs from Experiment B).

[0038] In Experiment A, participants were given a questionnaire using a 7-point scale to assess how much they applied to the following items. • Feeling uncomfortable I feel irritated. The voice sounds unnatural. • The audio is difficult to hear.

[0039] In this experiment, the acoustic signals modulated using the modulation functions corresponding to the first, second, and third examples of amplitude waveforms described above, and the fourth example of an acoustic signal having a pulse-like waveform were used for evaluation. The results are shown in Figure 7. Figure 7 shows the results of the experiment.

[0040] As shown in Figure 7, gamma wave induction was confirmed in all modulated waveform patterns. From this, it can be expected that when user US1 listens to the sound emitted from the acoustic output device 30 in this embodiment, gamma waves will be induced in user US1's brain. By inducing gamma waves in user US1's brain, it is possible to expect an improvement in user US1's cognitive function (for example, treatment or prevention of dementia). Furthermore, it was confirmed that the degree of discomfort was lower in the waveform patterns of the first to third examples than in the waveform pattern of the fourth example. From this, it can be expected that when using an acoustic signal modulated by the modulation function disclosed in this embodiment, the discomfort caused to the listener when listening to the sound will be suppressed compared to when using an acoustic signal consisting of simple pulse waves.

[0041] Furthermore, as shown in Figure 7, the degree of gamma wave induction was confirmed to be highest in the waveform pattern of Example 1 compared to Example 2 and Example 3. On the other hand, the degree of discomfort was lowest in Example 3 and highest in Example 2. From this, it can be expected that in this embodiment, when the envelope of the amplitude waveform of the output acoustic signal output by the signal processing device 10 to the acoustic output device 30 is in the shape of an inverted sawtooth wave, a high cognitive function improvement effect can be obtained while suppressing discomfort to the listener. Also, in this embodiment, it can be expected that discomfort to the listener will be further suppressed when the envelope of the amplitude waveform of the output acoustic signal output by the signal processing device 10 to the acoustic output device 30 is sinusoidal.

[0042] (2-5-2) Details of the experiment The above-mentioned experiments for verifying the effects of the technology disclosed herein will be described in more detail below. The following description will focus on experiments A and B, while experiment C will be omitted. In these experiments, we focus on brainwaves with a frequency of 40 Hz as the gamma waves to be induced. Figure 9 shows a list of the sound stimuli (output sounds) used in these experiments. Column 901 indicates the identification number of the sound stimulus (hereinafter referred to as the "stimulus number"), column 902 indicates the frequency of the sound signal (sine wave) before modulation, column 903 indicates whether modulation was performed and the modulation function used, column 904 indicates the frequency of the modulation function, and column 905 indicates the degree of modulation.

[0043] Nine types of stimuli were prepared as a group of sine wave stimuli (stimulus numbers "01" to "09"). First, a 40Hz sine wave was created as a comparison (stimulus number "01"). This stimulus is a pure sine wave and is not modulated. Next, a 1kHz continuous sine wave was modulated. Modulation was performed by multiplying the 1kHz sine wave by the following envelope. In addition to a normal sine wave (so-called AM modulation), sawtooth waves and inverse sawtooth waves were used as envelopes. Stimuli numbers "02" to "06" are sound stimuli modulated with a sine wave. The envelope of sine wave modulation is represented by equation (1).

number

[0044] Here, m is the modulation index, and 0.00, 0.50, and 1.00 were used. fm is the modulation frequency, and 20Hz, 40Hz, and 80Hz were used. t is the time. The sinusoidally modulated sound stimulus corresponds to the third example of the amplitude waveform described above. Next, stimulus numbers "07" and "08" are sawtooth wave modulated sound stimuli and inverse sawtooth wave modulated sound stimuli, respectively. The envelopes for sawtooth wave modulation and inverse sawtooth wave modulation are represented by equations (2) and (3), respectively.

number

[0045] The modulation index m was set to 1.00, and the modulation frequency fm was set to 40 Hz. The sawtooth-modulated sound stimulus and the inverse sawtooth-modulated sound stimulus correspond to the second and first examples of the amplitude waveforms described above, respectively. The sawtooth function used here is a discontinuous function that repeatedly increases linearly from -1 to 1, and then instantaneously returns to -1. The stimuli used in the experiment were adjusted so that their equivalent noise levels (Laeq) were equal after modulation. For example, the 40 Hz sine wave of stimulus number "01" has a sound pressure level that is 34.6 dB higher than that of 1 kHz when the equivalent noise levels are equalized, but this equalizes the perceived loudness.

[0046] In addition to these, we used the stimulus used in the research in Non-Patent Document 1 (a pulse train consisting of a 1kHz sine wave with a 0.3 ms taper applied to both ends, repeated at a period of 40Hz) as a comparison (stimulus number "09"). This pulse-wave-like sound stimulus corresponds to the fourth example of the amplitude waveform described above. The equivalent noise level of this stimulus was also matched to that of stimuli numbers "01" to "08".

[0047] Subsequently, to prevent noise at the start and end of playback, a 0.5-second taper was applied before and after the stimulus. By performing this final taper, the equivalent noise level in the steady-state section was strictly maintained. The stimulus duration was 10 seconds for the psychological experiment and 30 seconds for the electroencephalogram (EEG) measurement.

[0048] These stimuli were presented to the experiment participants in mono (diotic) mode via headphones with a Laeq of 60 dB. That is, the system was adjusted so that an unmodulated 1 kHz sine wave had a sound pressure level of 60 dB. Sound pressure calibration was performed using a dummy head. The experiment participants were 26 native Japanese speakers with normal hearing (22.7 ± 2.1 years old, 18 males + 8 females).

[0049] Prior to the electroencephalogram (EEG) measurement experiment, a psychological evaluation experiment (corresponding to Experiment A described above) was conducted for each stimulus. The length of the stimulus, including the tapered portion, was 10 seconds. Since all participants heard these stimulus sounds for the first time in this psychological experiment, it is thought that the effect of familiarity with each stimulus sound was minimal.

[0050] The experiment was conducted in the same quiet, magnetically shielded room used for electroencephalography (EEG) measurements, with participants wearing headphones. An LCD display was placed in front of the participants, and a GUI for psychological evaluation was provided. All responses were made using the mouse. The questions asked participants to rate the level of discomfort and irritation they felt upon hearing each sound stimulus on a 7-point scale. Each stimulus was played only once, and the UI was designed so that participants could not respond until the 10-second stimulus playback was complete. The system was set to automatically play the next stimulus after a response was completed. The system was also designed to automatically prompt participants to take breaks during the experiment.

[0051] Participants were instructed to "imagine that the sounds you hear in this experiment are being broadcast as audio from a television program, video streaming service, or radio, and that you are listening to them in your living room at home. Please judge how unnatural or difficult to hear the sounds are." They were also told that the meaning of the words played was irrelevant to the experiment. Prior to the experiment, participants performed a practice task using four stimuli. In the experiment, each participant's 7-point response was treated as a numerical scale from 1 to 7, and the arithmetic mean was calculated. This value was then averaged among the participants.

[0052] After the psychological experiment, electroencephalogram (EEG) measurements were taken (corresponding to Experiment B described above). The measurements were taken in a quiet, magnetically shielded room. The length of the stimulus used, including the tapered portion, was 30 seconds. During the experiment, the same processed stimulus was presented twice. The interval between stimuli was 5 seconds, and the presentation order was random. During the presentation of the stimuli, participants were instructed to remain as still as possible and to minimize blinking as much as possible. In addition, a silent short animated video was played on an LCD monitor, and the level of consciousness was controlled to remain constant and the attention level to remain consistently low. The video was selected by the participants from a pre-prepared selection. In addition to the A1 and A2 reference electrodes, active electrodes were placed on each participant at the positions of the Fp1, Fp2, F3, F4, T3, T4, T5, T6, Cz, and Pz channels using the 10-20 method.

[0053] The measured electroencephalogram (EEG) waveforms were analyzed after the experiment. First, the 1-second region tapers before and after the 30-second stimulus presentation interval were excluded from the analysis. Then, 55 1-second intervals were extracted, shifting by 0.5 seconds each. Since each of these intervals was presented twice after the same processing, there were 110 intervals to analyze. An FFT was performed on each of these 110 waveforms using a Hann window. Because the Hann window was applied by shifting the window by half each time, all time data were treated equally. From the FFT results, the ratio of the power of the 40Hz component to the sum of the power of the 14Hz to 100Hz components was calculated, and this was averaged over the 110 intervals to obtain one scalar value (called the 40Hz EEG power spectrum ratio) for each electrode of each participant. First, for each channel, the mean and standard deviation between subjects were calculated for each response to each stimulus. From this data, we investigated whether electroencephalogram elicitation was predominantly from the left or right side of the brain, and selected a representative electrode that appeared to be largely unaffected by electrical noise within that region. We then performed hypothesis testing on the values ​​of this electrode. For each stimulation group, we confirmed the differences using analysis of variance (ANOVA) and performed multiple comparison tests using Tukey's method.

[0054] Figure 10 shows the experimental results of electroencephalogram (EEG) elicitation by sound stimuli. Specifically, Figure 10 shows the power ratio of the 40Hz component of the EEG elicited by each stimulus in the T6 channel. The values ​​and error bars in the graph represent the mean and standard deviation of all experimental participants. Significant differences in stimuli were confirmed by ANOVA (p<0.01).

[0055] First, let's discuss stimuli using sine waves. Using an unmodulated 1kHz sine wave (stimulus number "05") as a reference, no difference was observed in the 40Hz component of the brainwaves between it and a 40Hz sine wave (stimulus number "01") (p=0.94). The equivalent noise levels of these stimuli were standardized, and their loudness was also nearly identical. This suggests that simply presenting a 40Hz low-frequency sound does not evoke a 40Hz component in the brainwaves. Furthermore, this indicates that the 40Hz component signal applied to the headphones was not detected by the brainwave electrodes as electrical noise. This is because the 40Hz component is most prominent in stimulus number "01". It was also found that the 40Hz component was not evoked by 20Hz sine wave modulation (stimulus number "02") or 80Hz sine wave modulation (stimulus number "06"). In addition, with 40Hz sinusoidal modulation (stimulus numbers "03", "04", and "05"), a tendency for a 40Hz component to be elicited in proportion to the modulation degree is observed.

[0056] In contrast, sawtooth wave modulation (stimulus number "07") and inverse sawtooth wave modulation (stimulus number "08") both showed a significant difference compared to the unmodulated 1kHz sine wave (stimulus number "05"). Furthermore, no significant difference was observed between these two stimuli. Therefore, this indicates that even with a 1kHz sound, not just a 40Hz low-frequency sound, setting the amplitude envelope of the modulation function to 40Hz can induce a 40Hz EEG component in the brain. In addition, pulsed stimuli (stimulus number "09") also showed a significant difference compared to the unmodulated 1kHz sine wave (stimulus number "05"). Furthermore, there was no significant difference between pulsed stimuli (stimulus number "09") and sawtooth wave modulation and inverse sawtooth wave modulation (stimuli numbers "07" and "08"). These data indicate that similar EEG induction effects can be obtained not only with pulsed sounds, but also with amplitude-modulated sine waves (sounds that retain the pitch of the original 1kHz sine wave).

[0057] Finally, we examine the relationship between the results of the psychological experiment and the electroencephalogram (EEG) measurements. Figure 11 shows the correlation between the results of the psychological experiment and the EEG measurements. Specifically, Figure 11 shows the relationship between the level of discomfort and the ratio of 40Hz EEG components.

[0058] A positive correlation was observed between the degree of discomfort and the ratio of 40Hz EEG activity (r=0.56). This suggests that, at least among the stimulus groups used in this study, there is a general tendency for higher levels of discomfort to be associated with greater 40Hz EEG activity. For example, the pulsed stimulus "09" elicits very high levels of discomfort, but also the strongest 40Hz EEG activity. However, the correlation is not very strong, so even if a regression line is drawn, some stimuli will deviate significantly from it. For example, stimulus "08," which is a sine wave modulated with an inverse sawtooth wave, is located above the regression line. While its discomfort level is significantly lower than that of stimulus "09," the decrease in the 40Hz EEG ratio is smaller than that of other stimuli. Conversely, stimulus "06," which is a sine wave modulated with an 80Hz sine wave, shows a small decrease in discomfort, but a significant decrease in the 40Hz EEG. Furthermore, stimulus number "07," which is a sine wave modulated with a sawtooth wave, showed lower levels of discomfort and a lower 40Hz EEG ratio compared to stimulus number "09," a pulsed stimulus, while showing slightly higher levels of discomfort and a lower 40Hz EEG ratio compared to stimulus number "08," which is inverse sawtooth wave modulated. Stimulus number "03," which is a 1kHz sine wave modulated with a 40Hz sine wave at 100% modulation, showed lower levels of discomfort and a lower 40Hz EEG ratio compared to stimulus number "09," a pulsed stimulus, while showing slightly lower levels of discomfort and a lower 40Hz EEG ratio compared to stimulus number "08," which is inverse sawtooth wave modulated.

[0059] (3) Acoustic signal processing The acoustic signal processing of this embodiment will now be described. Figure 8 is a diagram showing the overall flow of acoustic signal processing by the signal processing device 10 of this embodiment. The processing in Figure 8 is realized by the processor 12 of the signal processing device 10 reading and executing a program stored in the storage device 11. Note that at least a part of the processing in Figure 8 may be realized by one or more dedicated circuits.

[0060] The acoustic signal processing shown in Figure 8 starts when any of the following start conditions are met. The acoustic signal processing shown in Figure 8 was invoked by another process or an external instruction. The user performed an operation to invoke the acoustic signal processing shown in Figure 8. The signal processing device 10 has reached a predetermined state (for example, power-on). The designated date and time have arrived. A predetermined amount of time has elapsed since a predetermined event (for example, the activation of the signal processing device 10, or the previous execution of the acoustic signal processing in Figure 8).

[0061] As shown in Figure 8, the signal processing device 10 performs the acquisition of the input acoustic signal (S110). Specifically, the signal processing device 10 receives the input acoustic signal sent from the sound source device 50. In step S110, the signal processing device 10 may further perform A / D conversion of the input acoustic signal.

[0062] The input acoustic signal corresponds to at least one of the following, for example: • Musical content (e.g., singing, playing instruments, or a combination thereof (i.e., songs). This may include audio content accompanying video content.) • Audio content (e.g., readings, narrations, announcements, radio dramas, monologues, conversations, monologues, or combinations thereof; may include audio content accompanying video content). • Other audio content (e.g., electronic sounds, ambient sounds, or machine sounds) However, singing or audio content is not limited to sounds produced by human vocal organs, but may include sounds generated by speech synthesis technology. After step S110, the signal processing device 10 performs the determination of the modulation method (S111). Specifically, the signal processing device 10 determines a modulation method to be used to generate an output acoustic signal from the input acoustic signal acquired in step S110. The modulation method determined here includes, for example, at least one of a modulation function used for modulation processing and a modulation degree corresponding to the degree of amplitude change due to modulation. As an example, the signal processing device 10 selects which of the three types of modulation functions described with reference to Figures 4 to 6 to use. The selection of which modulation function to use may be determined based on input operations by the user or another party or external instructions, or it may be determined by an algorithm.

[0063] In this embodiment, "other person" refers to, for example, at least one of the following: • The user's family, friends, or acquaintances • Medical professionals (e.g., the user's doctor) • Creator or provider of content corresponding to the input audio signal • Provider of signal processing device 10 • Administrator of the facility used by the user

[0064] The signal processing device 10 may determine the modulation method based on, for example, the characteristics of the input acoustic signal (balance between speech and music, volume changes, type of music, timbre, or other characteristics) and user attribute information (age, gender, hearing ability, cognitive function level, user identification information, or other attribute information). This allows the signal processing device 10 to determine the modulation method in a way that enhances the cognitive function improvement effect of the modulation, or in a way that minimizes discomfort for the user. Alternatively, the signal processing device 10 may determine the modulation method according to a timer. By periodically changing the modulation method according to the timer, it is possible to suppress the user from becoming accustomed to the modulated sound and to efficiently stimulate the user's brain. Furthermore, similar to determining the modulation method, the signal processing device 10 may determine the volume of the output acoustic signal according to various conditions.

[0065] In step S111, the signal processing device 10 may decide not to perform modulation (i.e., to set the modulation level to 0) as one of the options for the modulation method. Alternatively, the signal processing device 10 may decide on a modulation method such that modulation is performed after a predetermined time has elapsed since the initial decision to perform no modulation. Furthermore, the signal processing device 10 may decide on a modulation method such that the modulation level gradually increases when the signal changes from a state where no modulation is performed to a state where modulation is performed.

[0066] After step S111, the signal processing device 10 generates an output acoustic signal by performing modulation of the input acoustic signal (S112). Specifically, the signal processing device 10 performs modulation processing on the input acoustic signal acquired in S110 according to the modulation method determined in S111. As an example, the signal processing device 10 performs amplitude modulation on the input acoustic signal using a modulation function with a frequency corresponding to a gamma wave (for example, a frequency between 35 Hz and 45 Hz). As a result, the input acoustic signal is given an amplitude change corresponding to the above frequency. In step S112, the signal processing device 10 may further perform at least one of the following: amplification of the output acoustic signal, volume adjustment, or D / A conversion.

[0067] After step S112, the signal processing device 10 performs the output acoustic signal transmission (S113). Specifically, the signal processing device 10 sends the output acoustic signal generated in step S112 to the acoustic output device 30. The acoustic output device 30 generates sound corresponding to the output acoustic signal. The signal processing device 10 completes the acoustic signal processing shown in Figure 8 in step S113. The signal processing device 10 may perform the processing shown in Figure 8 collectively for an input audio signal having a fixed playback period (for example, a single piece of music content), or it may repeat the processing shown in Figure 8 for each predetermined playback section of the input audio signal (for example, every 100ms). 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 processing shown in Figure 8 may be terminated according to specific termination conditions (for example, when a certain amount of time has elapsed, when a user operation has been performed, or when the output history of the modulated sound has reached a predetermined state). Furthermore, the order of processing by the signal processing device 10 is not limited to the example shown in Figure 8. For example, the determination of the modulation method (S111) may be performed before the acquisition of the input acoustic signal (S110).

[0068] (4) Summary As described above, the signal processing device 10 of this embodiment generates an output acoustic signal having an amplitude change corresponding to the frequency of gamma waves by performing amplitude modulation on the input acoustic signal. In the output acoustic signal, the rising and falling edges of the envelope of the amplitude waveform are asymmetric. The signal processing device 10 outputs the generated output acoustic signal to the acoustic output device 30. This makes it possible to increase or decrease the amplitude of the acoustic signal at a predetermined period while suppressing discomfort to the listener. The acoustic output device 30 then plays a sound corresponding to the output acoustic signal to the user, thereby inducing gamma waves in the user's brain due to the fluctuation in the amplitude of the output acoustic signal. As a result, an effect of improving the user's cognitive function (for example, treatment or prevention of dementia) can be expected.

[0069] The output acoustic signal may have amplitude changes corresponding to frequencies between 35 Hz and 45 Hz. This allows for the induction of gamma waves in the user's brain when the user is exposed to sounds corresponding to the output acoustic signal.

[0070] The input audio signal may be an audio signal corresponding to music content. This can increase the user's motivation to listen to the sound corresponding to the output audio signal.

[0071] Furthermore, since gamma wave induction was confirmed in all three waveform patterns during the experiment, input acoustic signals with the amplitude waveforms of the first, second, and third examples can be expected to improve the user's cognitive function (for example, in the treatment or prevention of dementia).

[0072] (5) Variant The storage device 11 may be connected to the signal processing device 10 via a network NW. The display 21 may be built into the signal processing device 10.

[0073] The above description shows an example in which the signal processing device 10 modulates the input acoustic signal. However, the signal processing device 10 may also extract a portion of the acoustic signal from the input acoustic signal, modulate only the extracted acoustic signal, and then generate the output acoustic signal.

[0074] The above description shows an example in which the signal processing device 10 modulates the input acoustic signal to generate an output acoustic signal, which is then sent to the acoustic output device 30. However, the signal processing device 10 may also generate an output acoustic signal by combining it with other acoustic signals to obtain a modulated input acoustic signal, and then send the generated output acoustic signal to the acoustic output device 30. Furthermore, the signal processing device 10 may simultaneously send the modulated input acoustic signal and other acoustic signals to the acoustic output device 30 without combining them.

[0075] In the above description, an example was shown in which the output acoustic signal generated by the signal processing device 10 modulating the input acoustic signal has an inverse sawtooth or sawtooth envelope of amplitude waveform, and the rising and falling edges of the envelope are asymmetrical. However, the output acoustic signal generated by the signal processing device 10 is not limited to these examples, and may have other amplitude waveforms in which the rising and falling edges of the envelope of amplitude waveform are asymmetrical.

[0076] For example, in the rising portion of the envelope, the slope of the tangent to the envelope may gradually decrease, or the slope of the tangent to the envelope may gradually increase. Also, for example, in the falling portion of the envelope, the slope of the tangent to the envelope may gradually decrease, or the slope of the tangent to the envelope may gradually increase.

[0077] The above explanation mainly described an example where the modulation function has frequencies between 35 Hz and 45 Hz. However, the modulation function used by the signal processing device 10 is not limited to this, and any modulation function that affects the induction of gamma waves in the listener's brain is acceptable. For example, the modulation function may have frequencies between 25 Hz and 140 Hz. Also, for example, the frequency of the modulation function may change over time, and the modulation function may partially have frequencies below 35 Hz or frequencies above 45 Hz.

[0078] The above description describes the case where the output acoustic signal generated by the signal processing device 10 is output to an acoustic output device 30 that emits a sound corresponding to the output acoustic signal for the user to hear. However, the destination of the output acoustic signal from 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 broadcast. In this case, the signal processing device 10 may output the input acoustic signal, which has not undergone modulation processing, to the external device along with the output acoustic signal generated by the modulation processing. This allows the external device to arbitrarily select and play either the unmodulated acoustic signal or the modulated acoustic signal.

[0079] Furthermore, the signal processing device 10 may output information indicating the content of the modulation process to an external device along with the output acoustic signal. The information indicating the content of the modulation process may include, for example, any of the following: • Information indicating the modulation function • Information indicating the degree of modulation • Information indicating volume This allows the external device to change the method of reproducing the acoustic signal according to the content of the modulation process. Furthermore, if the signal processing device 10 acquires additional information (for example, ID3 tags in an MP3 file) along with the input acoustic signal, it may modify the additional information and output it to an external device along with the output acoustic signal.

[0080] In the embodiments described above, the acoustic system 1, including the signal processing device 10, was primarily described as a cognitive function improvement system for improving cognitive function (e.g., treatment or prevention of dementia). 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-beta decreases and cognitive function improves. That is, by having the user listen to a sound corresponding to the output acoustic signal output by the signal processing device 10, it is expected that amyloid-beta in the user's brain will decrease and deposition will be suppressed, which will be useful in preventing or treating diseases caused by an increase or deposition of amyloid-beta. One example of a disease caused by amyloid-beta deposition is cerebral amyloid angiopathy (CAA). CAA is a disease in which amyloid-beta protein is deposited in the walls of small blood vessels in the brain, making the blood vessel walls fragile and increasing the likelihood of cerebral hemorrhage. Similar to dementia, there is no drug to treat CAA itself, so the technology described in the embodiments above could be an innovative treatment method. In other words, the acoustic system 1, which includes a signal processing device 10 and an acoustic output device 30 that allows the user to hear sounds corresponding to the output acoustic signals output by the signal processing device 10, can also be used as a medical system for the treatment or prevention of cerebral amyloid angiopathy.

[0081] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to the embodiments described above. Furthermore, the embodiments described above can be improved or modified in various ways without departing from the spirit of the present invention. In addition, the embodiments and modifications described above can be combined. [Explanation of symbols]

[0082] 1: Sound System 10: Signal Processing Device 11:Storage device 12: Processor 13: Input / Output Interface 14: Communication Interface 21: Display 30: Audio output device 50: Sound source device

Claims

1. A means for receiving instructions for processing acoustic signals, A means for outputting an output acoustic signal that generates a sound that induces gamma waves in the user's brain in response to the aforementioned instructions, A signal processing device having, The output acoustic signal has an amplitude change corresponding to a period that corresponds to a frequency between 35 Hz and 45 Hz, and the rising and falling edges of the envelope of the amplitude waveform are asymmetrical. Signal processing device.

2. The rising edge of the envelope of the amplitude waveform in the output acoustic signal is steeper than the falling edge of the envelope. The signal processing apparatus according to claim 1.

3. The falling edge of the envelope of the amplitude waveform in the output acoustic signal is steeper than the rising edge of the envelope. The signal processing apparatus according to claim 1.

4. The envelope of the amplitude waveform of the output acoustic signal is sawtooth or inverse sawtooth. The signal processing apparatus according to claim 1.

5. The system includes means for changing the degree of amplitude change in the output acoustic signal according to the period, according to a timer. The signal processing apparatus according to claim 1.

6. The means for making the change involves gradually increasing the degree of amplitude change according to the period when changing from a state in which there is no change in amplitude according to the period in the output sound signal to a state in which there is a change in amplitude according to the period in the output sound signal. The signal processing apparatus according to claim 5.

7. The degree of amplitude change in the output acoustic signal according to the period varies depending on the sound characteristics contained in the output acoustic signal. The signal processing apparatus according to claim 1.

8. The aforementioned sound characteristics relate to at least one of the following: the balance between speech and music, volume changes, type of music, and timbre. The signal processing apparatus according to claim 7.

9. The output audio signal includes music content or audio content. The signal processing apparatus according to any one of claims 1 to 7.

10. A system for improving the cognitive function of users, A signal processing device that outputs an output acoustic signal having an amplitude change corresponding to a period that corresponds to a frequency of 35 Hz or more and 45 Hz or less, and in which the rising and falling edges of the envelope of the amplitude waveform are asymmetrical. The system includes an acoustic output device that generates sound corresponding to the output acoustic signal output by the signal processing device, system.

11. A system for the treatment or prevention of diseases caused by an increase or deposition of amyloid-beta, A signal processing device that outputs an output acoustic signal having an amplitude change corresponding to a period that corresponds to a frequency of 35 Hz or more and 45 Hz or less, and in which the rising and falling edges of the envelope of the amplitude waveform are asymmetrical. The system includes an acoustic output device that generates sound corresponding to the output acoustic signal output by the signal processing device, system.

12. It accepts instructions for processing acoustic signals. In response to the above instructions, an output acoustic signal is generated that produces a sound that induces gamma waves in the user's brain. The output acoustic signal has an amplitude change corresponding to a period that corresponds to a frequency between 35 Hz and 45 Hz, and the rising and falling edges of the envelope of the amplitude waveform are asymmetrical. Signal generation method.

13. A program for causing a computer to function as one of the means of a signal processing device according to any one of claims 1 to 7.

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