Signal processing device, cognitive function improvement system, signal generation method, and program

Abstract

To provide a signal processing device, a cognitive function improvement system, a signal processing method, and a program.SOLUTION: In an acoustic system where a sound source device 50 and a signal processing device 10 are connected with each other via a predetermined interface that can transmit an acoustic signal and a sound output device 30 generates a sound according to an output acoustic signal that is obtained from the signal processing device 10, the signal processing device includes: means for receiving an input acoustic signal; means for obtaining a first acoustic signal having periodic changes corresponding to the frequency of a gamma wave; and means for outputting an output acoustic signal based on both the obtained first acoustic signal and a second acoustic signal based on the input acoustic signal.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] There is a research report that when a biological organism is made to perceive a pulsed sound stimulus at a frequency of about 40 times per second and gamma waves are induced in the brain of the biological organism, it is effective in improving the cognitive function of the biological organism (see Non-Patent Document 1). Gamma waves refer to those among the nerve oscillations captured by electrophysiological techniques such as electroencephalograms and magnetoencephalograms of the periodic nerve activities in the cerebral cortex, whose frequencies are included in the gamma band (25 to 140 Hz).

[0003] Patent Document 1 discloses adjusting the volume by increasing or decreasing the amplitude of a sound wave or a sound track in order to create a rhythmic stimulus corresponding to a stimulation frequency for inducing brain wave synchronization.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, increasing or decreasing the amplitude of an acoustic signal may make it difficult for listeners to hear the information contained in the signal (for example, singing or an announcement). In other words, increasing or decreasing the amplitude of an acoustic signal may impair the listener's acoustic experience.

[0007] The purpose of this disclosure is to change the amplitude of an acoustic signal while suppressing degradation of the acoustic experience. [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 acquiring a first acoustic signal having periodic fluctuations corresponding to the frequency of a gamma wave, and means for outputting an output acoustic signal based on the acquired first acoustic signal and a second acoustic signal based on the input acoustic signal. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of the acoustic system according to the first embodiment. [Figure 2] This is a block diagram showing the configuration of the signal processing device according to the first embodiment. [Figure 3] This is an explanatory diagram of one aspect of the first embodiment. [Figure 4] This figure shows the overall flow of acoustic signal processing by the signal processing device of the first embodiment. [Figure 5] This is a diagram illustrating the frequency characteristics of acoustic signals. [Figure 6] This is a diagram illustrating the temporal characteristics of acoustic signals. [Figure 7] This is a diagram illustrating the characteristics of the output of an acoustic signal. [Figure 8] This is an explanatory diagram of one embodiment of Modification 1. [Figure 9] This diagram shows the overall flow of acoustic signal processing by the signal processing device of Modification 1. [Figure 10]It is a diagram showing the overall flow of acoustic signal processing by the signal processing device of Modification 2. [Figure 11] It is a block diagram showing the configuration of the signal processing device of the second embodiment. [Figure 12] It is an explanatory diagram of one aspect of the second embodiment. [Figure 13] It is a diagram showing the overall flow of acoustic signal processing by the signal processing device of the second embodiment. [Figure 14] It is an explanatory diagram of the synthesis of the adjusted auxiliary acoustic signal in the second embodiment. [Figure 15] It is an explanatory diagram of the synthesis of the adjusted auxiliary acoustic signal in the second embodiment. [Figure 16] It is an explanatory diagram of the synthesis of the auxiliary acoustic signal in the second embodiment. [Figure 17] It is a diagram showing the experimental system. [Figure 18] It is a diagram showing the experimental results.

Mode for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present invention will be described in detail based on the drawings. In the drawings for explaining the embodiment, the same components are generally denoted by the same reference numerals, and the repeated explanation thereof will be omitted.

[0011] (1) First Embodiment The first embodiment will be described.

[0012] (1-1) Configuration of Acoustic System The configuration of the acoustic system will be described. FIG. 1 is a block diagram showing the configuration of the acoustic system of the first embodiment.

[0013] As shown in FIG. 1, the acoustic system 1 includes a signal processing device 10, an acoustic 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 acoustic signals. The interface may be, 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 also be a wireless interface using Bluetooth (registered trademark), etc. 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 the first embodiment includes either an analog signal or a digital signal, or both.

[0015] The signal processing device 10 performs acoustic signal processing on the input acoustic signal acquired from the sound source device 50. The acoustic signal processing by the signal processing device 10 includes at least acoustic signal modulation processing (details will be described later). The acoustic signal processing by the signal processing device 10 may also include acoustic signal conversion processing (e.g., separation, extraction, or synthesis). Furthermore, the acoustic signal processing by the signal processing device 10 may further include acoustic signal amplification processing similar to that of an AV amplifier. The signal processing device 10 sends the 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.

[0016] The sound output device 30 generates sound corresponding to the output sound signal acquired from the signal processing device 10. The sound output device 30 is, for example, a loudspeaker (which may include a speaker with a built-in amplifier (powered speaker)), headphones, or earphones. The audio output device 30 can also be configured as a single unit together with the signal processing device 10. Specifically, the signal processing device 10 and the audio output device 30 can be implemented in a TV, radio, music player, AV amplifier, speaker, headphones, earphones, smartphone, or PC. The signal processing device 10 and the audio output device 30 constitute a cognitive function improvement system.

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

[0018] (1-1-1) Configuration of the signal processing device The configuration of the signal processing device will now be described. Figure 2 is a block diagram showing the configuration of the signal processing device according to the first embodiment.

[0019] As shown in Figure 2, the signal processing device 10 comprises 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 the display 21.

[0020] 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.

[0021] The program includes, for example, the following: • OS (Operating System) programs • Programs for applications that perform information processing.

[0022] 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)

[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 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)

[0024] 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.

[0025] 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.

[0026] 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).

[0027] 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.

[0028] (1-2) One embodiment One aspect of the first embodiment will now be described. Figure 3 is an explanatory diagram of one aspect of the first embodiment.

[0029] (1-2-1) 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. Based on the input acoustic signal, the signal processing device 10 generates a plurality of intermediate acoustic signals, including a first acoustic signal and a second acoustic signal. In the example in Figure 3, the first acoustic signal is a partial signal corresponding to the acoustic component of the input acoustic signal that originates from an instrument, and the second acoustic signal is a partial signal corresponding to the acoustic component of the input acoustic signal that originates from a vocal.

[0030] The signal processing device 10 generates a modulated first acoustic signal by modulating the first acoustic signal, which is part of the intermediate acoustic signal. The modulation is amplitude modulation using a modulation function with a frequency of 35 Hz to 45 Hz, for example. As a result, the first acoustic signal has amplitude changes (volume strength) corresponding to the above frequency. The signal processing device 10 does not modulate the second acoustic signal, which is the remainder of the intermediate acoustic signal.

[0031] The signal processing device 10 generates an output acoustic signal based on the partially modulated intermediate acoustic signal (i.e., the modulated first acoustic signal and the second acoustic signal). The signal processing device 10 sends the output acoustic signal to the acoustic output device 30. The acoustic output device 30 generates sound corresponding to the output acoustic signal.

[0032] User US1 (an example of a "hearer") listens to the sound emitted from the sound output device 30. User US1 is, for example, a dementia patient, a person at risk of dementia, or a healthy person who expects to prevent dementia. As mentioned above, the output sound signal is based on a first sound signal modulated using a modulation function with a frequency between 35 Hz and 45 Hz. Therefore, when User US1 listens to the sound emitted from the sound output device 30, gamma waves are induced in User US1's brain. This can be expected to improve User US1's cognitive function (for example, in the treatment or prevention of dementia). On the other hand, since the second sound signal is not modulated, the deterioration of User US1's acoustic experience with respect to the second sound signal is suppressed.

[0033] (1-2-2) Experimental Results This section describes the experiments conducted to verify the effectiveness of the technology disclosed herein. In this experiment, 17 young subjects with normal hearing were exposed to output sounds based on acoustic signals generated by the technology disclosed herein, and the degree of gamma wave induction in the subjects' brains was evaluated. For comparison, the degree of gamma wave induction was also evaluated when subjects were exposed to output sounds based on acoustic signals generated by a method different from the technology disclosed herein. The degree of gamma wave induction was measured using electrodes attached to the subjects' heads. Headphones attached to the subjects' heads were used as the acoustic output device that emitted output sounds in response to the generated acoustic signals.

[0034] Figure 17 shows the experimental setup. Subjects were presented with auditory stimuli (output sounds) via headphones in a quiet, magnetically shielded room. An LCD monitor was placed in front of each participant, playing a short, silent animated video to maintain a consistent level of consciousness. Active electrodes for electroencephalography (EEG) measurement were placed on the participants' heads.

[0035] Recordings of TV news programs and music programs were prepared as auditory stimuli to be presented to the subjects. From the news programs, four sections were selected and used: the opening narration, economics, entertainment, and weather forecast. From the music programs, four sections were selected and used: two female solo singers, one male solo singer, and one male group. Furthermore, these sound sources (unmodulated sounds) were processed using the technology disclosed herein to generate partially modulated acoustic signals (partially modulated sounds). Specifically, commercially available audio separation software was used to separate the sound source into speech (human voice) and other background sounds. Then, the modulated background sound, obtained by amplitude modulating the background sound using a 40Hz sine wave as the modulation function, was combined with the unmodulated speech to generate partially modulated sounds. For comparison, an acoustic signal (whole modulated sound) was also generated by amplitude modulating the entire sound source before separation using the same modulation function. In addition, a 1kHz sine wave and a modulated sine wave obtained by modulating it with a 40Hz sine wave were generated. Furthermore, a sound consisting of a pulse train with a period of 40 Hz (each pulse containing one 1 kHz sine wave) was generated. In summary, the sound stimuli used in this experiment consisted of nine patterns: pulse train S1, modulated 1 kHz sine wave S2, unmodulated 1 kHz sine wave S3, fully modulated news audio S4, partially modulated news audio S5, unmodulated news audio S6, fully modulated music audio S7, partially modulated music audio S8, and unmodulated music audio S9.

[0036] Each of the above sound stimuli was 15 seconds long and presented randomly four times for each pattern. These stimuli were presented through headphones at an equivalent noise level of 72 dB. During the presentation of the stimuli, the Phase Locking Index (PLI) was calculated for each stimulus pattern from the electroencephalogram (EEG) waveform obtained from active electrodes placed on the subject's Cz.

[0037] Figure 18 shows the experimental results. Specifically, Figure 18 shows the mean and standard deviation of PLI for 17 subjects to nine patterns of sound stimuli from S1 to S9. As shown in Figure 18, an improvement in PLI was observed for all modulated sounds (S2, S4, S5, S7, and S8) compared to unmodulated sounds (S3, S6, and S9). The PLI for all unmodulated sounds was 0.03 or less. The PLI of partially modulated sounds (S5 and S8) generated using the technology of this disclosure is smaller than the PLI of fully modulated sounds (S2, S4, and S7), but significantly larger than the PLI of unmodulated sounds (S3, S6, and S9). Furthermore, while the speech portion (voice reading the news or singing voice) is modulated in the fully modulated sounds, the speech portion is not modulated in the partially modulated sounds, and therefore the clarity of the speech is not impaired. As a result, the acoustic experience for the listener is less degraded with partially modulated sounds than with fully modulated sounds. In other words, this experiment demonstrated that the technology disclosed herein can induce gamma waves in the user while suppressing the degradation of the acoustic experience. This result suggests that an acoustic system may be able to improve the user's cognitive function by outputting sound stimuli that are less likely to cause discomfort even when the user listens to them on a daily basis.

[0038] (1-3) Acoustic signal processing The acoustic signal processing of the first embodiment will now be described. Figure 4 is a diagram showing the overall flow of acoustic signal processing by the signal processing device of the first embodiment. The processing in Figure 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 Figure 4 may be realized by one or more dedicated circuits. The same applies to the processing in Figures 9 and 10, which will be described later. Figure 5 is an explanatory diagram of the frequency characteristics of the acoustic signal. Figure 6 is an explanatory diagram of the time characteristics of the acoustic signal. Figure 7 is an explanatory diagram of the output characteristics of the acoustic signal.

[0039] The acoustic signal processing shown in Figure 4 starts when any of the following start conditions are met. The acoustic signal processing shown in Figure 4 was invoked by another process or an external instruction. The user performed an operation to invoke the acoustic signal processing shown in Figure 4. 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 4).

[0040] As shown in Figure 4, 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.

[0041] 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.

[0042] After step S110, the signal processing device 10 performs the generation of an intermediate acoustic signal (S111). Specifically, the signal processing device 10 generates an intermediate acoustic signal containing multiple acoustic signals based on the input acoustic signal acquired in step S110.

[0043] The intermediate acoustic signal may comprise not only two but three or more acoustic signals, but the following description assumes that it comprises a first acoustic signal and a second acoustic signal. The first and second acoustic signals differ in at least one characteristic. For example, one of the first and second acoustic signals may possess a predetermined characteristic, while the other does not. Alternatively, one of the first and second acoustic signals may be qualitatively or quantitatively superior in a predetermined characteristic, while the other is qualitatively or quantitatively inferior in that characteristic. The characteristic may be determined based on input operations by the user or others or external instructions, or it may be determined by an algorithm. For example, the signal processing device 10 may determine the characteristics for generating the intermediate acoustic signal based on the results of analyzing the input acoustic signal.

[0044] In the following explanation, "others" refers to at least one of the following individuals, for example: • 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

[0045] The features may be at least one of the following, for example: • Sound characteristics (especially qualitative characteristics) • Frequency characteristics • Characteristics of time • Characteristics of amplitude • Output characteristics

[0046] The characteristics of sound are, for example, acoustic components that satisfy one or more qualitative conditions of sound. These qualitative conditions may be, for example, conditions relating to at least one of the following: • Type of sound source (e.g., object, instrument, vocal, music, conversational audio, or input channel) • Direction of sound arrival • Improvement of cognitive function, or prevention of dementia In the example shown in Figure 3, the first acoustic signal includes an acoustic component originating from a musical instrument, and the second acoustic signal includes an acoustic component originating from a vocal.

[0047] The frequency characteristics are, for example, acoustic components that satisfy a frequency condition of 1 or more. Specifically, as shown in Figure 5, the first acoustic signal does not contain acoustic components in a specific frequency band f1 to f2, while the second acoustic signal contains acoustic components in that frequency band f1 to f2. The specific frequency band can be determined, for example, based on the frequency band of the human voice.

[0048] A temporal characteristic is, for example, an acoustic component that satisfies one or more temporal conditions. Specifically, as shown in Figure 6, the first acoustic signal does not contain the acoustic component in a specific time interval t1 to t2, while the second acoustic signal contains that acoustic component. When defining an temporal characteristic as an acoustic component in multiple time intervals, each time interval may be set periodically or aperiodically.

[0049] The amplitude characteristic is, for example, an acoustic component that satisfies one or more amplitude conditions. As an example, the amplitude characteristic is that the change in volume over time matches a predetermined pattern.

[0050] The characteristics of the output are, for example, the sound (acoustic components) that a listener perceives as coming from a sound source located in a predetermined direction or position. Specifically, the characteristics of the output are, for example, acoustic components that satisfy one or more output conditions. As a first example, the output condition is that the sound output device 30 is associated with a speaker in a specific direction that constitutes the surround system (i.e., it is ultimately output from a specific speaker). In the example in Figure 7, the sound output device 30 corresponds to a surround speaker system including speakers 30-1 to 30-4. The first sound signal is associated with speakers 30-3 and 30-4 in a specific direction (i.e., output from the rear left or rear right), while the second sound signal is not associated with speakers 30-3 and 30-4 (instead, it is associated with speakers 30-1 and 30-2 (i.e., output from the front left or front right)). As a second example, the output condition is that the acoustic signal is associated with a virtual sound source set in a specific direction or position in object audio.

[0051] Step S111 can be omitted if the input audio signal acquired in step S110 has been pre-separated into audio signals having predetermined characteristics and audio signals not having those characteristics (for example, if the input audio signal corresponds to a multi-channel audio signal associated with each speaker constituting a surround sound system as an audio output device 30). In this case, the input audio signal is treated as an intermediate audio signal. On the other hand, if the input audio signal has not been pre-separated into audio signals having predetermined characteristics and audio signals not having those characteristics, the signal processing device 10 converts the input audio signal into an intermediate audio signal. For example, the signal processing device 10 extracts or separates audio signals having predetermined characteristics from the input audio signal.

[0052] After step S111, the signal processing device 10 performs the selection of the target signal (S112). Specifically, the signal processing device 10 selects a portion of the multiple acoustic signals (e.g., the first acoustic signal) included in the intermediate acoustic signal generated in step S111 as the target signal. Which acoustic signal is selected as the target signal may be determined based on input operations by the user or another party or external instructions, or it may be determined by an algorithm. For example, the signal processing device 10 may determine the target signal based on the characteristics of the acoustic signals included in the intermediate acoustic signal (balance between speech and music, volume changes, type of music, timbre, or other characteristics). This allows the signal processing device 10 to select a target signal that enhances the cognitive function improvement effect through modulation, or to select a target signal that minimizes discomfort for the user.

[0053] After step S112, the signal processing device 10 performs modulation of the target signal (S113). Specifically, the signal processing device 10 modulates the target signal selected in step S112. As an example, the signal processing device 10 performs amplitude modulation on the target signal using a modulation function with a frequency corresponding to a gamma wave (for example, a frequency between 35 Hz and 45 Hz). Specifically, if A(t) is a modulation function having a periodicity between 35 Hz and 45 Hz, X(t) is a function representing the waveform of the first acoustic signal before modulation, and Y(t) is a function representing the waveform of the modulated first acoustic signal, Y(t) = A(t)·X(t) This results in the target signal having an amplitude change corresponding to the above frequency.

[0054] After step S113, the signal processing device 10 performs the generation of an output acoustic signal (S114). Specifically, the signal processing device 10 generates an output acoustic signal based on the acoustic signals from the intermediate acoustic signals that were not selected as target signals in step S112 (hereinafter referred to as "non-target signals") and the target signals that were modulated in step S113. Step S114 can be omitted if the non-target signal and the modulated target signal match the output format of the sound output device 30 (for example, if the non-target signal and the modulated target signal correspond to multi-channel sound signals associated with each speaker constituting the surround system as the sound output device 30). In this case, the non-target signal and the modulated target signal are treated as output sound signals. On the other hand, if the non-target signal and the modulated target signal do not match the output format of the sound output device 30, the signal processing device 10 converts the non-target signal and the modulated target signal into an output sound signal. Specifically, the signal processing device 10 synthesizes two or more sound signals from the non-target signal and the modulated target signal, or extracts or separates a sound signal from at least one of the non-target signal and the modulated target signal. The method of synthesizing the sound signals is not limited, but may include, for example, signal summation, HRTF (Head Related Transfer Function) convolution, convolution of a transfer function that adds sound source position information, or summation after these convolution processes. In step S114, 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.

[0055] After step S114, the signal processing device 10 performs the output acoustic signal transmission (S115). Specifically, the signal processing device 10 sends the output acoustic signal generated in step S114 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 4 in step S115. The signal processing device 10 may perform the processing shown in Figure 4 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 4 for each predetermined playback interval 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 4 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).

[0056] (1-4) Summary As described above, the signal processing device 10 of the first embodiment generates a modulated first acoustic signal having amplitude changes corresponding to the frequency of gamma waves by amplitude modulating a first acoustic signal from the input acoustic signal that has predetermined characteristics. The signal processing device 10 outputs an output acoustic signal based on the modulated first acoustic signal and a second acoustic signal from the input acoustic signal that does not have predetermined characteristics. This makes it possible to increase or decrease the amplitude of the first acoustic signal at a predetermined period while suppressing deterioration of the acoustic experience related to the second acoustic signal. Furthermore, the acoustic output device 30 may play a sound corresponding to such output acoustic signal to the user (for example, a dementia patient, a person at risk of dementia, or a healthy person who expects to prevent dementia). This induces gamma waves in the user's brain due to fluctuations in the amplitude of the first acoustic signal. As a result, an improvement in the user's cognitive function (for example, treatment or prevention of dementia) can be expected.

[0057] The first acoustic signal may be an acoustic signal from the input acoustic signal that contains sounds (acoustic components) of a predetermined sound source type. This allows the amplitude of the first acoustic signal to be increased or decreased at a predetermined period while suppressing the degradation of the acoustic experience of sounds other than those of the predetermined sound source type.

[0058] The first acoustic signal may be an input acoustic signal that contains a sound (acoustic component) that the listener perceives as coming from a sound source in a predetermined direction. This allows the amplitude of the first acoustic signal to be increased or decreased at a predetermined period while suppressing the degradation of the acoustic experience other than the sound that the listener perceives as coming from a sound source in a predetermined direction.

[0059] The first acoustic signal may be an acoustic signal from the input acoustic signal that contains sounds (acoustic components) in a predetermined frequency band. This allows the amplitude of the first acoustic signal to be increased or decreased at a predetermined period while suppressing the degradation of the acoustic experience of sounds other than those in the predetermined frequency band.

[0060] The first acoustic signal may be an acoustic signal from the input acoustic signal that contains sound (acoustic components) within a predetermined time interval. This allows the amplitude of the first acoustic signal to be increased or decreased at a predetermined period while suppressing the degradation of the acoustic experience other than the sound within the predetermined time interval.

[0061] The second acoustic signal may be an acoustic signal obtained by separating the first acoustic signal from the input acoustic signal. As a result, the acoustic components that were included in the input acoustic signal are included in either the first or second acoustic signal, thus suppressing the deterioration of the acoustic experience that occurs due to the loss of acoustic components.

[0062] 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.

[0063] 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.

[0064] (1-5) Variations A modified example of the first embodiment will be described.

[0065] (1-5-1) Variation 1 Let's explain the first variation. The first variation is an example in which the first sound signal of the input sound signal is modulated with a first modulation degree, and the second sound signal is modulated with a second modulation degree that is different from the first modulation degree.

[0066] (1-5-1-1) One aspect of the modification 1 One embodiment of Modification 1 will be described. Figure 8 is an explanatory diagram of one embodiment of Modification 1.

[0067] As shown in Figure 8, the signal processing device 10 acquires an input acoustic signal from the sound source device 50. Based on the input acoustic signal, the signal processing device 10 generates a plurality of intermediate acoustic signals, including a first acoustic signal and a second acoustic signal. In the example in Figure 8, the first acoustic signal corresponds to the acoustic component of the input acoustic signal that originates from an instrument, and the second acoustic signal corresponds to the acoustic component of the input acoustic signal that originates from a vocal.

[0068] The signal processing device 10 generates a modulated first acoustic signal and a modulated second acoustic signal by modulating the first acoustic signal and the second acoustic signal contained in the intermediate acoustic signal, respectively. The modulation is amplitude modulation using a modulation function with a frequency of 35 Hz to 45 Hz, for example. As a result, the acoustic signal is given a change in amplitude corresponding to the above frequency.

[0069] However, the signal processing device 10 uses different modulation degrees for the first and second acoustic signals. For example, the signal processing device 10 modulates the first acoustic signal with a first modulation degree and modulates the second acoustic signal with a second modulation degree smaller than the first modulation degree. In other words, the amplitude change (volume intensity) corresponding to the frequency of the modulation function is relatively sharp in the modulated first acoustic signal, while the amplitude change corresponding to the above frequency is relatively gentle in the modulated second acoustic signal (small deviation from the original sound).

[0070] The signal processing device 10 generates an output acoustic signal based on the intermediate acoustic signals (i.e., the modulated first acoustic signal and the modulated second acoustic signal) which are modulated with partially different modulation in this manner. The signal processing device 10 sends the output acoustic signal to the acoustic output device 30. The acoustic output device 30 generates sound corresponding to the output acoustic signal.

[0071] User US1 listens to the sound emitted from the sound output device 30. As mentioned above, the output sound signal is based on a first sound signal and a second sound signal modulated using a modulation function with a frequency between 35 Hz and 45 Hz. Therefore, when user US1 listens to the sound emitted from the sound output device 30, gamma waves are induced in user US1's brain. This can be expected to improve user US1's cognitive function (for example, in the treatment or prevention of dementia). On the other hand, since the second sound signal is modulated with a relatively small second modulation degree, the deterioration of user US1's acoustic experience with respect to the second sound signal is suppressed.

[0072] (1-5-1-2) Acoustic signal processing The acoustic signal processing of Modification 1 will now be explained. Figure 9 is a diagram showing the overall flow of acoustic signal processing by the signal processing device of Modification 1.

[0073] The acoustic signal processing shown in Figure 9 starts when any of the following start conditions are met. The acoustic signal processing shown in Figure 9 was invoked by another process or an external instruction. The user performed an operation to invoke the acoustic signal processing shown in Figure 9. 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 9).

[0074] As shown in Figure 9, the signal processing device 10 performs the acquisition of the input acoustic signal (S110) and the generation of an intermediate acoustic signal (S111), similar to Figure 4.

[0075] After step S111, the signal processing device 10 performs the selection of the target signal (S212). Specifically, the signal processing device 10 selects a portion of the multiple acoustic signals included in the intermediate acoustic signal generated in step S111 (for example, a first acoustic signal) as the first target signal. Furthermore, the signal processing device 10 selects a portion of the multiple acoustic signals included in the intermediate acoustic signal generated in step S111 (for example, a second acoustic signal) as the second target signal. Which acoustic signal is selected as the first target signal or the second target signal may be determined based on input operations by the user or another person or external instructions, or it may be determined by an algorithm. For example, the signal processing device 10 may determine the first and second target signals based on the characteristics of the multiple acoustic signals included in the intermediate acoustic signal (balance between voice and music, volume changes, type of music, timbre, or other characteristics). This allows the signal processing device 10 to select the first and second target signals in a way that enhances the cognitive function improvement effect through modulation, or in a way that minimizes discomfort for the user. The first target signal and the second target signal may each be acoustic signals having different characteristics. Alternatively, one of the first target signal and the second target signal may be an acoustic signal having a predetermined characteristic, while the other is an acoustic signal that does not have that characteristic.

[0076] After step S212, the signal processing device 10 performs modulation of the target signal (S213). Specifically, the signal processing device 10 modulates the first target signal and the second target signal selected in step S212 with different modulation increments. As an example, the signal processing device 10 performs amplitude modulation on the first target signal and the second target signal using a modulation function with a frequency corresponding to a gamma wave (for example, a frequency between 35 Hz and 45 Hz) with different modulation increments. As a result, the first target signal and the second target signal are given amplitude changes corresponding to the above frequency. The first or second modulation degree may be determined based on input operations by the user or another party or external instructions, or it may be determined by an algorithm. For example, the signal processing device 10 may determine the first and second modulation degrees based on the characteristics of the first and second acoustic signals (balance between voice and music, volume changes, type of music, timbre, or other characteristics). This allows the signal processing device 10 to determine the first and second modulation degrees in a way that enhances the cognitive function improvement effect of modulation, or in a way that minimizes discomfort for the user.

[0077] After step S213, the signal processing device 10 performs the generation of an output acoustic signal (S214). Specifically, the signal processing device 10 generates an output acoustic signal based on the first target signal and the second target signal that were modulated in step S213. Step S214 can be omitted if the modulated first target signal and the modulated second target signal match the output format of the sound output device 30 (for example, if the modulated first target signal and the modulated second target signal correspond to multi-channel sound signals associated with each speaker constituting the surround system as the sound output device 30). In this case, the modulated first target signal and the modulated second target signal are treated as output sound signals. On the other hand, if the modulated first target signal and the modulated second target signal do not match the output format of the sound output device 30, the signal processing device 10 converts the modulated first target signal and the modulated second target signal into output sound signals. For example, the signal processing device 10 may synthesize two or more sound signals from the modulated first target signal and the modulated second target signal, or extract or separate a sound signal from at least one of the modulated first target signal and the modulated second target signal. In step S214, the signal processing device 10 may further perform at least one of the following: amplification of the output acoustic signal or D / A conversion.

[0078] However, if there are intermediate acoustic signals that were not selected as target signals in step S212 (hereinafter referred to as "non-target signals"), the signal processing device 10 may generate an output acoustic signal based on the modulated first target signal, the modulated second target signal, and the non-target signals.

[0079] After step S214, the signal processing device 10 sends out the output acoustic signal (S115), as shown in Figure 4. The signal processing device 10 completes the acoustic signal processing shown in Figure 9 in step S115.

[0080] (1-5-1-3) Summary As described above, the signal processing device 10 of Modified Example 1 amplitude modulates a first acoustic signal from among the intermediate acoustic signals based on the input acoustic signal at a first modulation degree, and amplitude modulates a second acoustic signal from among the intermediate acoustic signals at a second modulation degree different from the first modulation degree. This makes it possible to increase or decrease the amplitude of both the first and second acoustic signals at a predetermined period while suppressing the deterioration of the acoustic experience for acoustic signals that are amplitude modulated at a relatively small modulation degree. Furthermore, the acoustic output device 30 may play a sound corresponding to such output acoustic signal to the user (for example, a dementia patient, a person at risk of dementia, or a healthy person who expects to prevent dementia). This induces gamma waves in the user's brain due to fluctuations in the amplitude of the first and second acoustic signals. As a result, an effect of improving the user's cognitive function (for example, treatment or prevention of dementia) can be expected. The signal processing device 10 may, in the same manner as described above, amplitude modulate the first acoustic signal with a first modulation function and amplitude modulate the second acoustic signal with a second modulation function different from the first modulation function. In this case as well, the same effects as when using the first and second modulation levels can be expected.

[0081] (1-5-2) Variation 2 Let's explain Modification Example 2. Modification Example 2 is an example in which each acoustic signal included in the intermediate acoustic signal is modulated with an individual modulation degree.

[0082] (1-5-2-1) Acoustic signal processing The acoustic signal processing of Modification 2 will now be explained. Figure 10 is a diagram showing the overall flow of acoustic signal processing by the signal processing device of Modification 2.

[0083] The acoustic signal processing shown in Figure 10 starts when any of the following start conditions are met. The acoustic signal processing shown in Figure 10 was invoked by another process or an external instruction. The user performed an operation to invoke the acoustic signal processing shown in Figure 10. 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 last execution of the acoustic signal processing in Figure 10).

[0084] As shown in Figure 10, the signal processing device 10 performs the acquisition of the input acoustic signal (S110) and the generation of an intermediate acoustic signal (S111), similar to Figure 4.

[0085] After step S111, the signal processing device 10 performs modulation degree assignment (S312). Specifically, the signal processing device 10 assigns a modulation degree individually to each of the multiple acoustic signals included in the intermediate acoustic signal generated in step S111. Each acoustic signal is assigned a different modulation level. A modulation level of "0" may be assigned to any of the acoustic signals. In other words, modulation may not be performed on any of the acoustic signals included in the intermediate acoustic signal. The modulation degree assigned to each acoustic signal may be determined based on input operations by the user or another party or external instructions, or it may be determined by an algorithm. For example, the signal processing device 10 may determine each modulation degree based on the characteristics of multiple acoustic signals included in the intermediate acoustic signal (balance between speech and music, volume changes, type of music, timbre, or other characteristics). This allows the signal processing device 10 to determine the modulation degree in a way that enhances the cognitive function improvement effect of modulation, or in a way that minimizes discomfort for the user.

[0086] After step S312, the signal processing device 10 performs modulation of the intermediate acoustic signal (S313). Specifically, the signal processing device 10 modulates each acoustic signal included in the intermediate acoustic signal with the modulation degree assigned in step S312. As an example, the signal processing device 10 performs amplitude modulation on each acoustic signal using a modulation function with a frequency corresponding to a gamma wave (for example, a frequency between 35 Hz and 45 Hz) with the individually assigned modulation degree. As a result, each acoustic signal is given an amplitude change corresponding to the above frequency.

[0087] After step S313, the signal processing device 10 performs the generation of an output acoustic signal (S314). Specifically, the signal processing device 10 generates an output acoustic signal based on the intermediate acoustic signal modulated in step S313. Step S314 can be omitted if the modulated intermediate sound signal matches the output format of the sound output device 30 (for example, if the modulated intermediate sound signal corresponds to a multi-channel sound signal associated with each speaker constituting the surround system as the sound output device 30). In this case, the modulated intermediate sound signal is treated as the output sound signal. On the other hand, if the modulated intermediate sound signal does not match the output format of the sound output device 30, the signal processing device 10 converts the modulated intermediate sound signal into an output sound signal. For example, the signal processing device 10 may combine two or more of the multiple sound signals contained in the intermediate sound signal, or extract or separate a sound signal from at least one of the sound signals contained in the modulated intermediate sound signal. In step S314, the signal processing device 10 may further perform at least one of the following: amplification of the output acoustic signal or D / A conversion.

[0088] After step S314, the signal processing device 10 sends out the output acoustic signal (S115), as shown in Figure 4. The signal processing device 10 completes the acoustic signal processing shown in Figure 10 in step S115.

[0089] (1-5-2-2) Summary As described above, the signal processing device 10 of the modified example 2 amplitude modulates each acoustic signal included in the intermediate acoustic signal based on the input acoustic signal with individually assigned modulation increments. This suppresses the degradation of the acoustic experience for acoustic signals amplitude modulated with relatively small modulation increments, while increasing or decreasing the amplitude of acoustic signals assigned non-zero modulation in a predetermined period. Furthermore, the acoustic output device 30 may play a sound corresponding to such output acoustic signal to the user (for example, a dementia patient, a person at risk of dementia, or a healthy person who expects to prevent dementia). This induces gamma waves in the user's brain due to fluctuations in the amplitude of the acoustic signals assigned non-zero modulation increments. As a result, an improvement in the user's cognitive function (for example, treatment or prevention of dementia) can be expected. The signal processing device 10 may also modulate each acoustic signal included in the intermediate acoustic signal with a modulation function assigned to it individually, using the same processing as described above. In this case as well, the same effect as when using individually assigned modulation levels can be expected.

[0090] (2) Second Embodiment A second embodiment will be described.

[0091] (2-1) Configuration of the sound system The configuration of the acoustic system will now be described. The configuration of the acoustic system in the second embodiment is the same as that of the acoustic system in the first embodiment shown in Figure 1.

[0092] (2-1-1) Configuration of the signal processing device The configuration of the signal processing device will now be described. Figure 11 is a block diagram showing the configuration of the signal processing device according to the second embodiment.

[0093] As shown in Figure 11, the signal processing device 10 comprises 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 and a signal generator 22.

[0094] The storage device 11, processor 12, input / output interface 13, communication interface 14, and display 21 are the same as in the first embodiment.

[0095] The signal generator 22 generates an acoustic signal (hereinafter referred to as the "auxiliary acoustic signal") having periodic fluctuations corresponding to the frequency of gamma waves. The auxiliary acoustic signal is, for example, a signal having pulses with a period corresponding to the frequency of gamma waves, but is not limited to this. For example, the auxiliary acoustic signal may be a sine wave corresponding to the frequency of gamma waves, or it may be generated by applying amplitude modulation according to the frequency of gamma waves to any acoustic signal such as noise or music. Preferably, the auxiliary acoustic signal is predetermined or adjusted so that the component corresponding to the frequency of gamma waves is greater than a reference. The reference may be determined based on the component of the auxiliary acoustic signal that does not correspond to the frequency of gamma waves, or it may be determined based on the component of the input acoustic signal that corresponds to the frequency of gamma waves. When the reference is the input acoustic signal, the auxiliary acoustic signal is a signal that contains more components corresponding to the frequency of gamma waves than the input acoustic signal. Modulation as described in the first embodiment or its modifications may be performed to generate the auxiliary acoustic signal, or other modulation may be performed. The signal generator 22 is an example of an input device. The functions of the signal generator 22 may be implemented by the processor 12. In this case, the signal processing device 10 does not need to be connected to the signal generator 22.

[0096] (2-2) One embodiment A description of one aspect of the second embodiment will be given. Figure 12 is an explanatory diagram of one aspect of the second embodiment.

[0097] As shown in Figure 12, the signal processing device 10 acquires an input acoustic signal from the sound source device 50. The signal processing device 10 acquires an auxiliary acoustic signal. The signal processing device 10 adjusts the auxiliary acoustic signal based on the input acoustic signal. However, the adjustment can be omitted, in which case "adjusted auxiliary acoustic signal" should be read as "auxiliary acoustic signal" in the following explanation. The signal processing device 10 generates a synthesized acoustic signal by combining (adding) the adjusted auxiliary acoustic signal to the input acoustic signal.

[0098] Here, the adjusted auxiliary acoustic signal has amplitude changes (volume intensity) corresponding to frequencies between 35 Hz and 45 Hz, for example. Therefore, in the process of generating the synthesized acoustic signal, the periodic fluctuations corresponding to the gamma wave frequencies in the input acoustic signal are amplified.

[0099] The signal processing device 10 generates an output sound signal based on a synthesized sound signal in which periodic fluctuations corresponding to the frequency of gamma waves are amplified. In the example in Figure 12, the signal processing device 10 generates a stereo output sound signal based on the synthesized sound signal. The signal processing device 10 sends the output sound signal to the sound output device 30. The sound output device 30 generates sound corresponding to the output sound signal. The output sound signal output by the signal processing device 10 may be a one-channel signal or a signal with three or more channels, depending on the configuration of the sound output device 30.

[0100] User US1 listens to the sound emitted from the sound output device 30. User US1 is, 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 sound signal is based on a synthesized sound signal in which periodic fluctuations corresponding to the frequency of gamma waves are enhanced. Therefore, when User US1 listens to the sound emitted from the sound 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). On the other hand, since the synthesized sound signal contains components of the unmodulated input sound signal, the degradation of User US1's acoustic experience with respect to the input sound signal is suppressed.

[0101] (2-3) Acoustic signal processing The acoustic signal processing of the second embodiment will now be described. Figure 13 is a diagram showing the overall flow of acoustic signal processing by the signal processing device of the second embodiment. The processing in Figure 13 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 13 may be realized by one or more dedicated circuits. Figure 14 is an explanatory diagram of the synthesis of the adjusted auxiliary acoustic signal in the second embodiment. Figure 15 is an explanatory diagram of the synthesis of the adjusted auxiliary acoustic signal in the second embodiment. Figure 16 is an explanatory diagram of the synthesis of the auxiliary acoustic signal in the second embodiment.

[0102] The acoustic signal processing of the second embodiment may be started in response to the fulfillment of the same start conditions as the acoustic signal processing of the first embodiment.

[0103] As shown in Figure 13, the signal processing device 10 performs the acquisition of the input acoustic signal (S110) in the same manner as in the first embodiment.

[0104] After step S110, the signal processing device 10 performs the acquisition of an auxiliary acoustic signal (S411). Specifically, the signal processing device 10 acquires the auxiliary acoustic signal generated by the signal generator 22.

[0105] After step S411, the signal processing device 10 performs adjustment of the auxiliary acoustic signal (S412). Specifically, the signal processing device 10 adjusts the auxiliary acoustic signal based on the input acoustic signal acquired in step S110.

[0106] As a first example of adjusting the auxiliary acoustic signal (S412), the signal processing device 10 obtains an adjusted auxiliary acoustic signal by adjusting the auxiliary acoustic signal so that the amplitude of the periodic fluctuation (e.g., pulse component) corresponding to the frequency of the gamma wave contained in the auxiliary acoustic signal follows the amplitude change of the input acoustic signal. The signal processing device 10 may adjust the auxiliary acoustic signal to follow the instantaneous value of the input acoustic signal, or it may adjust the auxiliary acoustic signal to follow the average value of the input acoustic signal in a time window of a predetermined width. As an example, the signal processing device 10 determines the amount of amplitude adjustment of the auxiliary acoustic signal so that the signal-to-noise ratio (S / N) of the input acoustic signal and the adjusted auxiliary acoustic signal are constant. According to the first example of adjusting the auxiliary acoustic signal (S412), as shown in Figure 14, the user can hear a sound in which the periodic fluctuation corresponding to the frequency of the gamma wave is enhanced. In this example, the magnitude of the amplitude of the periodic fluctuation corresponding to the frequency of the gamma wave contained in the adjusted auxiliary acoustic signal changes to follow the amplitude change of the input acoustic signal. Therefore, fluctuations in how the auxiliary audio signal is perceived (its prominence relative to the input audio signal) when the volume of the input audio signal changes are suppressed, and the degradation of the user's audio experience is minimized. In addition, even if the volume of the input audio signal changes, the user can continuously receive sound stimuli corresponding to gamma wave frequencies.

[0107] As a second example of adjusting the auxiliary acoustic signal (S412), the signal processing device 10 obtains an adjusted auxiliary acoustic signal by adjusting the auxiliary acoustic signal so that the amplitude of the periodic fluctuation (e.g., pulse component) corresponding to the frequency of the gamma wave contained in the auxiliary acoustic signal changes in the opposite direction to the amplitude change of the input acoustic signal. For example, the signal processing device 10 adjusts the auxiliary acoustic signal so that it follows an index that increases as the signal value of the input acoustic signal decreases. For example, such an index may be the reciprocal of the instantaneous value of the input acoustic signal, or it may be a value obtained by subtracting the instantaneous value from a fixed value. Alternatively, such an index may be the reciprocal of the average value of the input acoustic signal in a time window of a predetermined width, or it may be a value obtained by subtracting the average value from a fixed value. According to the second example of adjusting the auxiliary acoustic signal (S412), as shown in Figure 15, the user can hear a sound in which the periodic fluctuation corresponding to the frequency of the gamma wave is enhanced. In this example, the amplitude of the periodic fluctuations corresponding to the gamma wave frequencies in the adjusted auxiliary acoustic signal changes in the opposite direction to the amplitude changes of the input acoustic signal. Therefore, these periodic fluctuations become larger in silent sections of the input acoustic signal, while they are suppressed in other sections. Consequently, the periodic fluctuations corresponding to the gamma wave frequencies are amplified in sections that are less likely to interfere with the appreciation of sound based on the input acoustic signal, thus suppressing the degradation of the user's acoustic experience.

[0108] This step is optional; in this case, "adjusted auxiliary acoustic signal" should be read as "auxiliary acoustic signal" in the following explanation. Even if the adjustment of the auxiliary acoustic signal (S412) is omitted, as shown in Figure 16, the user can hear a sound with enhanced periodic fluctuations corresponding to the gamma wave frequency. By omitting the adjustment of the auxiliary acoustic signal (S412), the computational load on the signal processing device 10 can be reduced.

[0109] After step S412, the synthesis of the acoustic signal (S413) is performed. Specifically, the signal processing device 10 generates a synthesized acoustic signal by combining the input acoustic signal acquired in step S110 with the adjusted auxiliary acoustic signal obtained in step S412.

[0110] After step S413, the signal processing device 10 performs the generation of an output acoustic signal (S414). Specifically, the signal processing device 10 generates an output acoustic signal based on the synthesized acoustic signal generated in step S413. Step S414 can be omitted if the synthesized sound signal matches the output format of the sound output device 30 (for example, if the synthesized sound signal corresponds to a multi-channel sound signal associated with each speaker constituting the surround system as the sound output device 30). In this case, the synthesized sound signal is treated as the output sound signal. On the other hand, if the synthesized sound signal does not match the output format of the sound output device 30, the signal processing device 10 converts the synthesized sound signal into an output sound signal. Specifically, the signal processing device 10 synthesizes two or more sound signals from the synthesized sound signal, or extracts or separates a sound signal from at least one of the synthesized sound signals. The method of synthesizing the sound signals is not limited, but may include, for example, signal summation, HRTF (Head Related Transfer Function) convolution, convolution of a transfer function that adds sound source position information, or summation after these convolution processes. In step S414, 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.

[0111] After step S414, the signal processing device 10 performs the output acoustic signal transmission (S115). Specifically, the signal processing device 10 sends the output acoustic signal generated in step S414 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 13 in step S115. The signal processing device 10 may perform the processing shown in Figure 13 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 13 for each predetermined playback interval 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 13 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).

[0112] (2-4) Summary As described above, the signal processing device 10 of the second embodiment acquires an auxiliary acoustic signal having periodic fluctuations corresponding to the frequency of gamma waves and outputs an output acoustic signal based on the auxiliary acoustic signal and the input acoustic signal. This allows for an acoustic experience related to the input acoustic signal while increasing or decreasing the amplitude of the output acoustic signal at a predetermined period. Furthermore, the acoustic output device 30 may play a sound corresponding to the output acoustic signal to the user (for example, a dementia patient, a person at risk of dementia, or a healthy person who hopes to prevent dementia). This induces gamma waves in the user's brain due to fluctuations in the amplitude of the auxiliary acoustic signal. As a result, an improvement in the user's cognitive function (for example, treatment or prevention of dementia) can be expected.

[0113] The auxiliary acoustic signal may be a signal having pulses with a period corresponding to the frequency of gamma waves. This allows the auxiliary acoustic signal to be generated by simple hardware or processing.

[0114] The amplitude of the pulses included in the auxiliary acoustic signal may vary according to the amplitude of the input acoustic signal. This suppresses the adverse effects of components corresponding to gamma wave frequencies on the acoustic experience based on the input acoustic signal, making it easier for the user to accept the sound of those components.

[0115] (3) Other variations 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.

[0116] The above description of the first embodiment showed an example in which at least one acoustic signal included in an intermediate acoustic signal based on an input acoustic signal is modulated. However, an output acoustic signal may be generated based on an input acoustic signal and a modulated acoustic signal that does not originate from the input acoustic signal.

[0117] 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.

[0118] 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. 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 sound source corresponding to the modulated target signal. • Information indicating the channel corresponding to the modulated target signal. • Information indicating the characteristics of the modulated target signal • 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.

[0119] Modifications 1 and 2 illustrate examples of applying different modulation levels to different acoustic signals. However, it is also possible to apply different modulation functions to different acoustic signals.

[0120] In the second embodiment, an example was shown in which an adjusted auxiliary acoustic signal is combined with an input acoustic signal. However, the adjusted auxiliary acoustic signal may be combined with any of the acoustic signals described in the first embodiment or each of the modifications. For example, the output acoustic signal may be output after the adjusted auxiliary acoustic signal has been combined with it. The acoustic signal to be combined with the adjusted acoustic signal (hereinafter referred to as the "base acoustic signal") may be, for example, the input acoustic signal, an intermediate acoustic signal, a modulated acoustic signal, or an output acoustic signal. Furthermore, if the input acoustic signal, intermediate acoustic signal, modulated acoustic signal, or output acoustic signal contains multiple acoustic signals, all of these acoustic signals may be used as the base acoustic signal, or only some of them may be used as the base acoustic signal. In this modification, the amplitude of the auxiliary acoustic signal may be adjusted according to the change in the amplitude of the base acoustic signal.

[0121] In the second embodiment, an example was shown in which an auxiliary acoustic signal is adjusted based on an input acoustic signal. However, instead of adjusting the auxiliary acoustic signal, the signal processing device 10 may switch whether or not to synthesize the auxiliary acoustic signal based on the input acoustic signal. As a first example, the auxiliary acoustic signal may be synthesized with the input acoustic signal when the amplitude of the input acoustic signal exceeds a threshold or falls below a threshold. As a second example, the auxiliary acoustic signal may be synthesized with the input acoustic signal when the period during which the amplitude of the input acoustic signal exceeds a first threshold or the period during which the amplitude falls below a second threshold exceeds a third threshold.

[0122] The embodiments described above primarily focused on the use of the acoustic system, including the signal processing device 10, as a cognitive function improvement system for improving cognitive function (e.g., treatment or prevention of dementia). However, the uses of the signal processing device 10 are 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.

[0123] 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]

[0124] 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. means for receiving instructions for performing audio signal processing; means for outputting an output acoustic signal in response to the instruction; A signal processing device comprising: the first sound component and the second sound component included in the output sound signal have amplitude changes according to a predetermined period, a change in amplitude of the second sound component according to the predetermined period is smaller than a change in amplitude of the first sound component according to the predetermined period; Signal processing device.

2. means for receiving instructions for performing audio signal processing; means for outputting an output acoustic signal in response to the instruction; A signal processing device comprising: the first acoustic component included in the output acoustic signal has an amplitude change according to a predetermined period; the second acoustic component included in the output acoustic signal does not have a change in amplitude according to the predetermined period; Signal processing device.

3. the output acoustic signal produces a sound that induces gamma waves in the user's brain; 3. The signal processing device according to claim 1 or 2.

4. a degree of change in amplitude of the first sound component according to the predetermined period is determined based on an input operation; 3. The signal processing device according to claim 1 or 2.

5. a degree of change in amplitude of the first sound component according to the predetermined period differs depending on a feature of a sound included in the output sound signal; 3. The signal processing device according to claim 1 or 2.

6. a degree of change in amplitude of the first sound component according to the predetermined period differs depending on a balance of a plurality of sound components included in the output sound signal; 3. The signal processing device according to claim 1 or 2.

7. The first sound component and the second sound component differ in characteristics related to at least one of the type of sound source, the direction from which the sound arrives, the frequency, the time, the amplitude, and the output.

3. The signal processing device according to claim 1 or 2.

8. the first sound component includes a background sound other than a human voice, and the second sound component includes a human voice; 3. The signal processing device according to claim 1 or 2.

9. The predetermined period corresponds to a frequency of 35 Hz or more and 45 Hz or less.

3. The signal processing device according to claim 1 or 2.

10. the first acoustic component has a pulse of the predetermined period; 3. The signal processing device according to claim 1 or 2.

11. the output audio signal comprises music or speech content; 3. The signal processing device according to claim 1 or 2.

12. A cognitive function improvement system for improving a user's cognitive function, a signal processing device according to claim 1 or 2; an audio output device that generates a sound corresponding to the output audio signal output by the signal processing device, Cognitive function improvement system.

13. Accepting instructions for performing acoustic signal processing; generating an output acoustic signal in response to said instruction; the first sound component and the second sound component included in the output sound signal have amplitude changes according to a predetermined period, a change in amplitude of the second sound component according to the predetermined period is smaller than a change in amplitude of the first sound component according to the predetermined period; Signal generation method.

14. Accepting instructions for performing acoustic signal processing; generating an output acoustic signal in response to said instruction; the first acoustic component included in the output acoustic signal has an amplitude change according to a predetermined period; the second acoustic component included in the output acoustic signal does not have a change in amplitude according to the predetermined period; Signal generation method.

15. the output acoustic signal induces gamma waves in the user's brain; 15. The signal generating method according to claim 13 or 14.

16. A program for causing a computer to function as each of the means of the signal processing device according to claim 1 or 2.

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