Noise cancelling system

Abstract

To improve a noise canceling effect in a hybrid noise canceling system.SOLUTION: A noise canceling system includes: an input unit 10 that inputs noise signals from a microphone that collects external noise; a digital unit 20 that filters the noise signals with a digital filter circuit and outputs a first noise cancellation signal; an analog unit 30 that outputs a second noise cancellation signal that has been filtered; a synthesis unit 40 that synthesizes the first noise cancellation signal and the second noise cancellation signal to output a third noise cancellation signal; an output unit 70 that outputs an output signal by adding the third noise cancellation signal to an audio signal from a sound source; and a feedback unit 50 that feeds back a control signal based on the first noise cancellation signal and the second noise cancellation signal to the analog unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification relates to a noise cancellation system.

Background Art

[0002] Active noise control (ANC) is a technology that uses phase interference to cancel out sound by generating a sound with an opposite phase from a separately prepared control sound source for the sound to be reduced, and is widely used as a noise control or noise canceller function for earphones and headphones. For example, Patent Document 1 discloses a hybrid-type noise cancellation system configured to complement the noise reduction level and the band in which noise reduction is possible by a noise cancellation signal formed in a digital section and a noise cancellation signal formed in an analog path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventional hybrid-type noise cancellation system, if the characteristics of analog signal processing and digital signal processing are significantly different from each other, the noise cancellation effect will decrease.

[0005] Therefore, this specification has been made in view of the above-described problems, and an object thereof is to improve the noise cancellation effect in a hybrid-type noise cancellation system.

Means for Solving the Problems

[0006] According to one or more embodiments of the present specification, an input unit that inputs a noise signal from a microphone that picks up external noise, an A / D conversion circuit that converts the noise signal into a digital signal, a digital filter circuit that filters the digital signal, and a D / A conversion circuit that converts the filtered digital signal into a first noise cancellation signal of an analog signal. A digital unit including: an analog unit that outputs a second noise cancellation signal obtained by filtering the noise signal; a combining unit that outputs a third noise cancellation signal obtained by combining the first noise cancellation signal and the second noise cancellation signal; an output unit that outputs an output signal obtained by adding the third noise cancellation signal to an audio signal from a sound source; and a feedback unit that feeds back a control signal based on the first noise cancellation signal and the second noise cancellation signal to the analog unit. A noise cancellation system is provided.

Advantages of the Invention

[0007] According to the present specification, the effect of noise cancellation in a hybrid type noise cancellation system can be improved.

[0008] Both the foregoing description and the following detailed description of the present specification are exemplary and explanatory, and are to be understood as providing a further explanation of the disclosure recited in the claims.

[0009] The accompanying drawings, which are included to provide a further understanding of the present specification and are incorporated in and constitute a part of this application, illustrate embodiments and aspects of the present specification and together with the description serve to explain the principles of the present specification.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Referring in detail to the embodiments of this specification, examples thereof can be illustrated in the accompanying drawings. In the following description, when a detailed description of well-known functions or configurations obscures the gist of this specification unnecessarily, the detailed description can be omitted for the sake of brevity. The described steps and / or progress of operations are exemplary, but the order of steps and / or operations is not limited to those described in this specification and can be changed except for steps and / or operations that necessarily occur in a specific order.

[0012] Unless otherwise specified, the same reference signs can refer to components that are generally similar even if they are shown in different drawings. In one or more embodiments, components with the same name (or components with the same name) in different drawings can have the same or substantially the same functions and characteristics unless otherwise specified. Each name of the components used in the following description is selected for convenience and may be different from the actual product.

[0013] The advantages and features of this specification and the methods for achieving them will become apparent by referring to various examples described in detail hereinafter based on the accompanying drawings. However, this specification is not limited to the embodiment disclosed below and can be implemented in various different forms. An embodiment of this specification, etc. is only provided to complete the disclosure of this specification and to fully inform those with ordinary knowledge in the technical field to which the technical idea of this specification belongs of the scope of the technical idea.

[0014] When terms such as "including", "having", "consisting of", "comprising", "formed" are used in this specification, other parts can be added unless "only" or "solely" is used. The terms used in this specification are only used to describe a specific embodiment and are not intended to limit the scope shown in this specification. The terms used in this specification are only used to explain exemplary embodiments and are not intended to limit the scope shown in this specification. Terms expressing components in the singular include cases where they include a plurality unless otherwise explicitly stated. An "embodiment" can be an exemplary example. Any implementation described as an "embodiment" or "an example" in this specification does not necessarily have to be interpreted as being preferred and advantageous compared to other implementations.

[0015] In the case of the description of the time relationship, when the time sequence relationship is described by "after", "subsequent", "next", "before (or preceding or prior to)", etc., as long as "just", "immediate(ly)", or "direct(ly)" is not used, it can include both continuous and non - continuous cases.

[0016] Terms such as "first", "second", etc. are used to describe various components, but these components are not limited to these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below may also be the second component within the technical concept of this specification. Furthermore, the first element, the second element, etc. can be arbitrarily named according to the convenience of those skilled in the art without departing from the scope of this specification. Terms such as "first", "second", etc. can be used to distinguish components from each other, but the function or structure of the components is not limited by the ordinal number before the component or the name of the component.

[0017] When describing the components of this specification, terms such as "first", "second", "A", "B", "(a)", "(b)", etc. can be used. Such terms are for distinguishing the component from other components and are not used to define the essence, basis, order, or number of the component.

[0018] The term "at least one" should be understood to include all combinations that can be presented from one or more related items. For example, the meaning of "at least one of the first item, the second item, and the third item" can be understood to include not only combinations of two or more items presented from the first item, the second item, or the third item, but also any combination of the first item, the second item, and the third item.

[0019] The expression "a first component, a second component `and / or` a third component" shall be understood to mean one of the first, second, and third components, or any combination or all combinations of the first, second, and third components. For example, A, B, and / or C can be regarded as only A, only B, only C, any or some combination of A, B, and C, or all of A, B, and C. Further, the expression "component A / component B" shall be understood to mean component A and / or component B.

[0020] In one or more embodiments, the terms "between" and "among" may be used interchangeably for convenience unless otherwise specified. For example, the expression "between a plurality of components" can also be understood as "among a plurality of components". In other embodiments, the expression "among a plurality of components" can also be understood as "between a plurality of components". In one or more embodiments, the number of components can be 2. In one or more embodiments, the number of components may be more than 2.

[0021] In one or more embodiments, the expression "different from each other" can be understood such that any component is different from other components.

[0022] In one or more embodiments, the expressions "one or more of" and "one or more among" may be used interchangeably for convenience unless otherwise specified. For example, the expression "one or more of" can also be understood as "one or more among". For example, the expression "one or more among" can also be understood as "one or more of".

[0023] Each feature of one or more embodiments herein can be partially or wholly combined or combined with each other, enabling various technical linkages and drives, and each embodiment can be implemented independently of each other, or can also be implemented together in an associated relationship. In one or more embodiments, the components of each device according to various embodiments herein can be operably coupled or configured.

[0024] As used herein, terms (including technical and scientific terms) can have the same meaning as those understood by a person of ordinary skill in the art to which this specification pertains. Further, terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted as being idealized or having an overly formal meaning, unless otherwise specifically stated.

[0025] [First Embodiment] Hereinafter, embodiments according to this specification will be described in detail with reference to the drawings. Elements having the same function throughout the drawings are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0026] FIG. 1 is a block diagram showing an overall configuration example of a noise canceling system 1 according to this embodiment. The noise canceling system 1 is a feedback type noise canceling system. The feedback type is a control method that acquires the actual situation in real time and determines a control input based thereon.

[0027] The noise canceling system 1 performs signal processing on a noise signal obtained by picking up external noise such as noise generated by a noise source NS, and generates a noise canceling signal for canceling the noise signal. Then, the noise canceling system 1 outputs an output audio obtained by synthesizing the noise canceling signal and an audio signal such as music input from a sound source S. At this time, the output audio output by the noise canceling system 1 and the noise sound generated by the noise source NS enter the user's ear canal. Since the noise sound is canceled by the component of the noise canceling signal included in the output audio, the user can listen only to the audio based on the audio signal input from the sound source S.

[0028] As shown in FIG. 1, the noise canceling system 1 includes an input unit 10, a digital unit 20, an analog unit 30, a first synthesizing unit 40, a feedback unit 50, a second synthesizing unit 60, and an output unit 70.

[0029] The input unit 10 includes a microphone and a microphone amplifier, and is configured to be able to pick up external noise and the sound emitted from the output unit 70. The input unit 10 outputs the sound picked up by the microphone as a noise signal. The feedback method attenuates external noise by feeding back the inverted-phase component (noise cancellation signal) of the signal (noise signal) picked up by the input unit 10.

[0030] The digital unit 20 sequentially performs A / D conversion processing, digital filtering, and D / A conversion processing on the noise signal to generate a first noise cancellation signal for reducing noise.

[0031] FIG. 2 is a block diagram showing a configuration example of the digital unit 20 in the present embodiment. The digital unit 20 includes an ADC 21, a DSP 22, and a DAC 23. The ADC 21 is an A / D conversion circuit that converts a noise signal into a digital signal. The DSP 22 is a type of microprocessor and is a digital filter circuit that filters the digital signal converted by the ADC 21. The DAC 23 converts the digital signal filtered by the DSP 22 into an analog first noise cancellation signal.

[0032] The analog unit 30 is an analog circuit that outputs a second noise cancellation signal obtained by filtering the noise signal.

[0033] FIG. 3 is a block diagram showing a configuration example of the analog unit 30 in the present embodiment. The analog unit 30 includes an analog filter 31 and an inversion circuit 32. The analog filter 31 filters the noise signal which is an analog signal. The inversion circuit 32 performs a phase inversion of the analog signal filtered by the analog filter 31 to generate a second noise cancellation signal.

[0034] The characteristics of the analog filter 31 (first analog filter) are controlled based on a control signal from a feedback unit 50 described later. The analog filter 31 includes a resistance element, a capacitance element, and an operational amplifier. At least one of the resistance value of the resistance element and the capacitance value of the capacitance element changes according to the control signal.

[0035] Examples of the analog filter 31 include a low-pass filter. The cut-off frequency of the low-pass filter is preferably set so that the noise cancellation effect is maximized. In the present embodiment, as will be described later, the cut-off frequency can be controlled based on a control signal.

[0036] Specific examples of the low-pass filter include a Bessel filter, a Chebyshev filter, a Butterworth filter, etc. The Bessel filter is a type of linear filter in electronics engineering and signal processing, and is characterized in that the group delay is maximally flat (linear phase response). The Bessel filter is often used in circuits that separate high and low frequency ranges. The Bessel filter is more preferable than other filters in that its group delay characteristic is the flattest. However, the Bessel filter is the worst in terms of attenuation in the stop band. Therefore, when applying the Bessel filter, it is important to appropriately adjust the relationship between the cut-off frequency and the group delay characteristic.

[0037] For example, when the setting of the cut-off frequency in the low-pass filter is inappropriate, the phase difference between the noise signal and the noise cancellation signal for the noise signal deviates from 180° near the cut-off frequency, and the noise signal and the noise cancellation signal reinforce each other. As a result, an increase in the noise signal triggers howling. In this case, it is preferable to lower the cut-off frequency in the analog unit 30.

[0038] FIG. 4 is a circuit diagram showing a configuration example of the analog unit 30 in the present embodiment. Here, the analog unit 30 includes resistor elements R1 to R2, capacitor elements D1 to D2, an operational amplifier OP, etc. The resistor elements R1 to R2, the capacitor elements D1 to D2, and the operational amplifier OP constitute an inverting amplification type low-pass filter circuit.

[0039] The resistor elements R1 to R2 are variable resistor elements such as a potentiometer, for example, and can change their resistance values according to the control signals CT-1 and CT-3.

[0040] The capacitor elements D1 to D2 are composed of variable capacitance diodes or the like, and the capacitance can be changed by the voltage between the terminals (control signals CT-2 and CT-4).

[0041] The operational amplifier OP is an operational amplifier. The operational amplifier includes a non-inverting input terminal (+), an inverting input terminal (-), and an output terminal.

[0042] In FIG. 4, when the input noise signal IN is filtered by the resistor elements R1 to R2, the capacitor elements D1 to D2, and the operational amplifier OP, a second noise cancellation signal is output. According to the control signals CT-1 to CT-4, the resistor elements R1 to R2 and the capacitor elements D1 to D2 change, and the cut-off frequency and phase of the low-pass filter can change. Note that the control target by the control signal may be not only the cut-off frequency and phase but also characteristics such as gain. Also, the control signals CT-1 to CT-4 may be the same signals as the control signals supplied from the feedback unit 50, or may be signals obtained by adding different bias voltages to the same control signal.

[0043] The first synthesizing unit 40 generates a third noise cancellation signal obtained by synthesizing the first noise cancellation signal and the second noise cancellation signal. The third noise cancellation signal is output to the feedback unit 50 and the second synthesizing unit 60. Here, the third noise cancellation signal is a signal obtained by adding the first noise cancellation signal and the second noise cancellation signal.

[0044] The feedback unit 50 filters the third noise cancellation signal input from the first synthesizing unit 40 and feeds back a control signal to the analog unit 30. The analog unit 30 of the present embodiment can change characteristics such as the cut-off frequency, phase, and gain of the above-described low-pass filter based on the control signal.

[0045] The second synthesizing unit 60 generates an output signal obtained by adding the third noise cancellation signal from the feedback unit 50 to the audio signal from the sound source S.

[0046] The output unit 70 includes a power amplifier, a driver circuit, and a speaker. The output unit 70 drives the speaker with the output signal synthesized by the second synthesizing unit 60. As a result, external noise is canceled in the user's ear, and the user can enjoy only the audio signal.

[0047] FIGS. 5A to 5C are block diagrams showing various configuration examples of the feedback unit 50 in the present embodiment. The feedback unit 50 is a circuit that blocks a signal having a predetermined frequency component among the input signals. The feedback unit 50 can be constructed by various circuits such as an analog circuit, a digital circuit, or a combination of an analog circuit and a digital circuit.

[0048] In the first configuration example shown in FIG. 5A, the feedback unit 50 is constituted by an analog circuit and includes an analog filter 51 and a level detection circuit 52.

[0049] The analog filter 51 is a second analog filter that filters the input third noise cancellation signal. Examples of the analog filter 51 include a low-pass filter and the like, similar to the analog filter 31.

[0050] The level detection circuit 52 includes an integration circuit, detects the level of the analog signal output from the analog filter 51, and generates a control signal according to the detected level.

[0051] In the second configuration example shown in FIG. 5B, the feedback unit 50 is constituted by a digital circuit and includes an ADC 53, a DSP 54, and a DAC 55. The ADC 53, the DSP 54, and the DAC 55 have the same functions as the above-described ADC 21, DSP 22, and DAC 23.

[0052] The ADC (second A / D conversion circuit) 53 performs A / D conversion on the third noise cancellation signal into a second digital signal. The DSP (second digital filter circuit) 54 filters the A / D-converted second digital signal. The DAC (second D / A conversion circuit) 55 outputs a control signal obtained by D / A converting the filtered digital data to the analog unit 30.

[0053] In the third configuration example shown in FIG. 5C, the feedback unit 50 is a hybrid circuit including an analog circuit (analog filter 51 / level detection circuit 52) and a digital circuit (ADC 53 / DSP 54 / DAC 55).

[0054] FIG. 6 is a diagram showing the characteristics of the noise cancellation system 1 in the present embodiment. The vertical axis represents the volume, and the horizontal axis represents time (seconds). Waveform A is the waveform of the output audio when the ANC function is OFF. On the other hand, waveform B is the waveform of the output audio when the ANC function is ON. FIG. 6 shows that a noise cancellation effect of 7.8 dB is produced when the ANC function is turned ON.

[0055] Figure 7 is a diagram showing the specification of the noise canceling system 1 in the present embodiment. The vertical axis represents the volume output with respect to the signal, and the horizontal axis represents the frequency (Hz) of the signal. The waveform of symbol P represents the frequency characteristics when the ANC function is OFF. On the other hand, the waveform of symbol Q represents the frequency characteristics when the ANC function is ON. Comparing the waveform P and the waveform Q, it can be seen that the noise canceling effect is particularly large in the frequency band of 10 to 1000 Hz.

[0056] As described above, the noise canceling system 1 according to the present embodiment feeds back a control signal based on the first noise canceling signal and the second noise canceling signal from the digital unit 20 to the analog unit 30. For this reason, the second noise canceling signal of the analog unit 30 can be dynamically controlled according to the processing of the digital unit 20. As a result, it is possible to reduce the deterioration of the noise canceling effect caused by the characteristic difference between the digital unit 20 and the analog unit 30, and improve the noise canceling effect.

[0057] In particular, the analog unit 30 can change the characteristics of the analog filter 31, such as the cut-off frequency, gain, and phase, based on the control signal, and can improve the noise canceling effect.

[0058] Further, the analog filter 31 includes a resistance element and a capacitance element, and at least one of the resistance value of the resistance element and the capacitance value of the capacitance element is changed by the control signal. Thereby, the characteristics of the analog filter 31 can be changed.

[0059] [Second Embodiment] In the present embodiment, a modification of the noise canceling system 1 in the first embodiment will be described. The noise canceling system 2 in the present embodiment includes an input unit 10, a digital unit 20, an analog unit 30, a first combining unit 40, a feedback unit 50, a second combining unit 60, and an output unit 70, similarly to the first embodiment. Since the configuration of each unit is substantially the same as that of the first embodiment, the description of the overlapping parts will be omitted, and the differences will be described.

[0060] FIG. 8 is a block diagram showing an overall configuration example of the noise canceling system 2 in the present embodiment. In FIG. 8, unlike FIG. 1, an arrow indicating the direction of the control signal output from the feedback unit 50 to the digital unit 20 is described. However, the control signal fed back to the digital unit 20 may be different from the control signal fed back to the analog unit 30.

[0061] That is, the noise canceling system 2 of the present embodiment is different from the noise canceling system 1 of the first embodiment in that the feedback unit 50 further has a configuration in which a control signal based on the first noise canceling signal and the second noise canceling signal is fed back to the digital unit 20.

[0062] The digital unit 20 may include an adaptive digital filter that attenuates signal components other than noise based on a control signal.

[0063] As described above, according to the present embodiment, since the digital unit 20 can change the characteristics of the digital filter according to the control signal, it is possible to reduce the deterioration of the noise canceling effect caused by the characteristic difference between the digital unit 20 and the analog unit 30. Further, by including an adaptive digital filter that attenuates signal components other than noise based on a control signal in the digital unit 20, the effect of noise canceling can be further improved.

[0064] [Third Embodiment] In the present embodiment, a modification of the noise canceling system 1 in the first embodiment will be described. Since the configurations of the respective parts denoted by the same reference numerals are substantially the same as those in the first embodiment, the description of the overlapping parts will be omitted, and the differences will be described.

[0065] In the above-described first and second embodiments, the feedback unit 50 generated a control signal based on a third noise cancellation signal obtained by adding the first noise cancellation signal and the second noise cancellation signal. However, the control signal may be generated based on the difference between the first noise cancellation signal and the second noise cancellation signal.

[0066] FIG. 9 is a block diagram showing an overall configuration example of the noise canceling system 3 in the present embodiment. The noise canceling system 3 in the present embodiment includes a subtraction unit 80. The subtraction unit 80 outputs the difference between the first noise cancellation signal output from the digital unit 20 and the second noise cancellation signal output from the analog unit 30 to the feedback unit 50. That is, the feedback unit 50 in the present embodiment performs filtering and level detection on the difference between the first noise cancellation signal and the second noise cancellation signal, and feeds back the control signal to the analog unit 30.

[0067] As described above, according to the present embodiment, the control signal is generated based on the difference between the first noise cancellation signal and the second noise cancellation signal. Since the analog unit 30 is controlled so that the difference becomes small, the difference in characteristics between the digital unit 20 and the analog unit 30 can be further reduced. As a result, it is possible to reduce the deterioration of the noise canceling effect due to the difference in characteristics between the digital unit 20 and the analog unit 30, and improve the noise canceling effect.

[0068] [Modified Embodiment] In the above-described first to third embodiments, a feedback-type noise canceling system has been described. However, the system to which the present invention is applicable is not limited to the feedback type, but is also applicable to a feedforward-type noise canceling system. Further, the noise canceling system may have a system configuration that combines the feedforward method and the feedback method.

[0069] FIG. 10 is a block diagram showing an overall configuration example of a noise canceling system 4 in a modified embodiment. The noise canceling system 4 is a feedforward type noise canceling system. The feedforward method is a control method that determines a control input while predicting an operation based on a model of the system without acquiring an actual situation. The microphone of the input unit 10 of the noise canceling system 4 is configured to be able to pick up external noise without picking up the signal emitted from the speaker. As a result, at the user's ear, the external noise is canceled, and the user can enjoy only the audio signal.

[0070] The present specification described above is not limited to the above-described embodiments and the attached drawings, and it is obvious to those having ordinary knowledge in the technical field to which the present specification belongs that various substitutions, modifications, and changes are possible without departing from the technical idea of the present specification. Therefore, the scope of the present specification is indicated by the claims described later, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present specification.

Description of Reference Numerals

[0071] 1, 2, 3, 4 Noise canceling system 10 Input unit 20 Digital unit 21 ADC 22 DSP 23 DAC 30 Analog unit 31 Analog filter 32 Inverting circuit 40 First synthesizing unit 50 Feedback unit 51 Analog filter 52 Level detection circuit 53 ADC 54 DSP 55 DAC 60 Second synthesizing unit 70 Output unit 80 Subtraction Unit NS Noise Source S Sound Source

Claims

1. An input unit that inputs a noise signal from a microphone that picks up external noise, A digital unit including an A / D conversion circuit that converts the noise signal into a digital signal, a digital filter circuit that filters the digital signal, and a D / A conversion circuit that converts the filtered digital signal into a first noise cancellation signal of an analog signal, An analog unit that outputs a second noise cancellation signal obtained by filtering the noise signal, A combining unit that outputs a third noise cancellation signal obtained by combining the first noise cancellation signal and the second noise cancellation signal, An output unit that outputs an output signal obtained by adding the third noise cancellation signal to an audio signal from a sound source, A feedback unit that feeds back a control signal based on the first noise cancellation signal and the second noise cancellation signal to the analog unit, A noise cancellation system comprising the above.

2. The analog unit includes a first analog filter, The characteristics of the first analog filter are controlled based on the control signal, The noise cancellation system according to Claim 1.

3. The first analog filter includes a resistance element and a capacitance element, At least one of the resistance value of the resistance element and the capacitance value of the capacitance element is changed by the control signal, The noise cancellation system according to Claim 2.

4. The capacitance element is a variable capacitance diode, The noise cancellation system according to Claim 3.

5. The resistance element is a potentiometer, The noise cancellation system according to Claim 3.

6. The first analog filter is a low-pass filter, The cut-off frequency of the low-pass filter changes based on the control signal, The noise cancellation system according to Claim 2.

7. The gain of the first analog filter changes based on the control signal, The noise cancellation system according to Claim 2.

8. The phase of the first analog filter changes based on the control signal, The noise cancellation system according to Claim 2.

9. The first analog filter is a Bessel filter, The noise cancellation system according to Claim 2.

10. The feedback unit is A second analog filter that filters the third noise cancellation signal; A level detection circuit that detects the level of the signal output from the second analog filter and generates the control signal according to the level; comprising The noise cancellation system according to claim 1.

11. The feedback unit A second A / D conversion circuit that converts the third noise cancellation signal into a second digital signal; A second digital filter circuit that filters the second digital signal; A second D / A conversion circuit that converts the filtered second digital signal into the control signal; comprising The noise cancellation system according to claim 1.

12. The feedback unit generates the control signal by performing analog filtering and digital filtering on the third noise cancellation signal in parallel. The noise cancellation system according to claim 1.

13. The feedback unit further feeds back the control signal to the digital unit. The noise cancellation system according to claim 1.

14. The characteristics of the digital filter circuit of the digital unit are controlled based on the control signal converted into digital. The noise cancellation system according to claim 13.

15. The digital unit includes an adaptive digital filter that attenuates frequency components other than the external noise based on the control signal. The noise cancellation system according to claim 13.

16. The control signal is generated based on the third noise cancellation signal. The noise cancellation system according to claim 1.

17. The control signal is generated based on the difference between the first noise cancellation signal and the second noise cancellation signal. The noise cancellation system according to claim 1.

18. The output unit includes a speaker driven by the output signal, The microphone is configured to be able to pick up the signal emitted from the speaker and the external noise. The noise cancellation system according to claim 1.

19. The output unit includes a speaker driven by the output signal, The microphone is configured to not pick up the signal emitted from the speaker and to be able to pick up the external noise. The noise canceling system according to claim 1.

20. An input unit for inputting a noise signal from a microphone that picks up external noise, A digital unit including an A / D conversion circuit that converts the noise signal into a digital signal, a digital filter circuit that filters the digital signal, and a D / A conversion circuit that converts the filtered digital signal into a first noise canceling signal of an analog signal, A control method for a noise canceling system having an analog unit that outputs a second noise canceling signal obtained by filtering the noise signal, Outputting a third noise canceling signal obtained by synthesizing the first noise canceling signal and the second noise canceling signal; Outputting an output signal obtained by adding the third noise canceling signal to an audio signal from a sound source; Feeding back a control signal based on the first noise canceling signal and the second noise canceling signal to the analog unit; A control method for a noise canceling system comprising the steps of:

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