Noise Cancelling System

Abstract

To improve the effect of noise canceling in a hybrid noise canceling system. [Solution] The noise canceling system includes an input unit 10 that inputs a noise signal from a microphone that picks up external noise, a digital unit 20 that filters the noise signal using a digital filter circuit and outputs a first noise cancellation signal, an analog unit 30 that outputs a second noise cancellation signal obtained by filtering the noise signal, a synthesis unit 40 that outputs a third noise cancellation signal that synthesizes the first noise cancellation signal and the second noise cancellation signal, an output unit 70 that outputs an output signal that adds 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.

Description

[Technical field]

[0001] The present specification relates to a noise canceling system. [Background technology]

[0002] Active noise control (ANC) is a technology that uses phase interference to eliminate a sound to be reduced by generating a sound of an opposite phase from a separately prepared control sound source, and is widely used as a noise control function or a noise canceller function for earphones and headphones. For example, Patent Document 1 discloses a hybrid noise canceling system configured to complement the band in which noise reduction is possible and the level of noise reduction 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] JP 2013-238870 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a conventional hybrid noise canceling system, if the characteristics of the analog signal processing and the digital signal processing differ significantly from each other, the noise canceling effect decreases.

[0005] Therefore, the present specification has been made in consideration of the above-mentioned problems, and has an object to improve the effect of noise canceling in a hybrid type noise canceling system. [Means for solving the problem]

[0006] According to one or more embodiments of the present specification, there is provided a noise canceling system including: 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 an analog signal, a first noise cancellation signal; an analog unit that outputs a second noise cancellation signal obtained by filtering the noise signal; a synthesis unit that outputs a third noise cancellation signal obtained by synthesizing 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. Effect of the Invention

[0007] According to the present specification, it is possible to improve the effect of noise canceling in a hybrid noise canceling system.

[0008] Both the foregoing description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the disclosure as set forth in the appended claims.

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

[0010] [Figure 1] 1 is a block diagram showing an example of the overall configuration of a noise canceling system according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing an example of the configuration of a digital section in the first embodiment. [Diagram 3] FIG. 2 is a block diagram showing an example of the configuration of an analog section in the first embodiment. [Figure 4] 2 is a circuit diagram showing a configuration example of an analog unit in the first embodiment. FIG. [Figure 5A] FIG. 2 is a block diagram showing a first exemplary configuration of a feedback section in the first embodiment. [Figure 5B] FIG. 4 is a block diagram showing a second exemplary configuration of the feedback unit in the first embodiment. [Figure 5C] FIG. 13 is a block diagram showing a third exemplary configuration of the feedback unit in the first embodiment. [Figure 6] FIG. 2 is a diagram illustrating characteristics of the noise canceling system according to the first embodiment. [Figure 7] FIG. 4 is a diagram illustrating characteristics of the noise cancellation system according to the first embodiment. [Figure 8] FIG. 11 is a block diagram showing an example of the overall configuration of a noise canceling system according to a second embodiment. [Figure 9] FIG. 11 is a block diagram showing an example of the overall configuration of a noise canceling system according to a third embodiment. [Figure 10] FIG. 13 is a block diagram showing an example of the overall configuration of a noise canceling system according to a modified embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Reference will now be made in detail to the embodiments of the present specification, examples of which may be illustrated in the accompanying drawings. In the following description, if a detailed description of a well-known function or configuration unnecessarily obscures the gist of the present specification, the detailed description may be omitted for the sake of brevity. The progression of steps and / or operations described is exemplary, but the order of steps and / or operations is not limited to that described herein and may be modified, except that steps and / or operations necessarily occur in a particular order.

[0012] Unless otherwise specified, the same reference numerals may generally refer to similar components even if they are illustrated in different drawings. In one or more embodiments, the same components (or components having the same name) in different drawings may have the same or substantially the same functions and characteristics, unless otherwise specified. The names of the respective components used in the following description are selected for convenience and may differ from the actual products.

[0013] The advantages and features of the present specification and methods for achieving them will become apparent from various examples described below in detail with reference to the accompanying drawings. However, the present specification is not limited to the embodiment disclosed below, and may be realized in various different forms, and the embodiment etc. of the present specification are provided only to complete the disclosure of the present specification and to fully inform those skilled in the art of the technical idea of ​​the present specification of the scope of the technical idea.

[0014] When the terms "comprise", "have", "consist", "comprise", "formed", etc. mentioned in this specification are used, other parts can be added unless "only" or "only" is used. The terms used in this specification are used only to describe a particular embodiment and are not intended to limit the scope of the specification. The terms used in this specification are used only to describe an exemplary embodiment and are not intended to limit the scope of the specification. Terms expressing elements in the singular include the plural unless otherwise expressly stated. An "embodiment" may be an illustrative example. Any implementation described in the "embodiment" or "example" described in this specification is not necessarily to be construed as preferred or advantageous over other implementations.

[0015] In describing a temporal relationship, when the temporal sequence is described using "after," "subsequent," "next," "before, preceding, or prior to," etc., it can also include consecutive or non-consecutive cases, since "just," "immediately," or "directly" are not used.

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

[0017] In describing components of this specification, terms such as first, second, A, B, (a), (b), etc. may be used. Such terms are used to distinguish the components from other components, and are not used to define the nature, basis, order, or number of the components.

[0018] The term "at least one" should be understood to include all possible combinations of one or more of the associated items. For example, the meaning of "at least one of the first, second, and third items" may include only any combination of the first, second, and third items, and not just combinations of items presented from two or more of the first, second, or third items.

[0019] The phrase "first component", "second component" and / or "third component" should be understood as one of the first, second and third components or any or all combinations of the first, second and third components. For example, A, B and / or C can be considered as A only, B only, C only, any or some combination of A, B and C, or all of A, B and C. Furthermore, the phrase "component A / component B" should be understood as component A and / or component B.

[0020] In one or more embodiments, the terms "between" and "in" may be used interchangeably for convenience only, unless otherwise specified. For example, the phrase "between multiple components" may also be understood as "among multiple components." In other embodiments, the phrase "among multiple components" may also be understood as "between multiple components." In one or more embodiments, the number of components may be two. In one or more embodiments, the number of components may be more than two.

[0021] In one or more embodiments, the term "different from each other" may be understood to mean that any component is different from the other component.

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

[0023] The features of one or more embodiments of the present specification may be combined or combined with each other in part or in whole, and various technical interlocking and operation may be possible, and each embodiment may be implemented independently of each other, or may be implemented together in a linked relationship. In one or more embodiments, the components of each device according to various embodiments of the present specification may be operably coupled or configured.

[0024] The terms used in this specification (including technical and scientific terms) may have the same meaning as that understood by a person having ordinary knowledge in the technical field to which this specification belongs. Furthermore, terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant technology, and should not be interpreted as idealized or overly formal unless otherwise specified.

[0025] [First embodiment] Hereinafter, embodiments of the present specification will be described in detail with reference to the drawings. Elements having common functions throughout the drawings will be designated by the same reference numerals, and duplicate descriptions may be omitted or simplified.

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

[0027] The noise canceling system 1 performs signal processing on a noise signal that picks up external noise such as noise generated by a noise source NS, and generates a noise cancellation signal that cancels the noise signal. The noise canceling system 1 then outputs an output sound that is a combination of the noise cancellation signal and an audio signal such as music input from a sound source S. At this time, the output sound output by the noise canceling system 1 and the noise sound generated by the noise source NS enter the user's ear canal. The noise sound is canceled by the components of the noise cancellation signal contained in the output sound, so the user can hear only the sound 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 section 10, a digital section 20, an analog section 30, a first synthesis section 40, a feedback section 50, a second synthesis section 60, and an output section .

[0029] The input unit 10 includes a microphone and a microphone amplifier, and is configured to be able to pick up external noise and 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 the external noise by feeding back the reverse phase component (noise cancellation signal) of the signal (noise signal) picked up by the input unit 10.

[0030] The digital section 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 that reduces noise.

[0031] 2 is a block diagram showing an example of the configuration of the digital unit 20 in this 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 a first noise cancellation signal that is an analog signal.

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

[0033] 3 is a block diagram showing an example of the configuration of the analog unit 30 in this embodiment. The analog unit 30 includes an analog filter 31 and an inversion circuit 32. The analog filter 31 filters a noise signal, which is an analog signal. The inversion circuit 32 inverts the phase 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, which will be described later. The analog filter 31 includes a resistive element, a capacitive element, and an operational amplifier. At least one of the resistance value of the resistive element and the capacitance value of the capacitive element changes according to the control signal.

[0035] The analog filter 31 may be a low-pass filter. The cutoff frequency of the low-pass filter is preferably set so as to maximize the noise canceling effect. In this embodiment, the cutoff frequency can be controlled based on a control signal, as described later.

[0036] Specific examples of low-pass filters include the Bessel filter, Chebyshev filter, and Butterworth filter. The Bessel filter is a type of linear filter used in electronics and signal processing, characterized by a maximally flat group delay (linear phase response). Bessel filters are often used in circuits that separate high and low frequencies. The Bessel filter is preferable to other filters in that it has the flattest group delay characteristics. However, the Bessel filter is the poorest in terms of attenuation in the cutoff range. Therefore, when applying a Bessel filter, it is important to properly adjust the relationship between the cutoff frequency and the group delay characteristics.

[0037] For example, if the cutoff frequency of the low-pass filter is not set appropriately, the phase difference between the noise signal and the noise cancellation signal for the noise signal will deviate from 180° near the cutoff frequency, and the noise signal and the noise cancellation signal will reinforce each other. As a result, the increase in the noise signal may trigger feedback. In this case, it is preferable to lower the cutoff frequency in the analog section 30.

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

[0039] The resistance elements R1 and R2 are variable resistance elements such as potentiometers, and the resistance value can be changed according to the control signals CT-1 and CT-3.

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

[0041] An operational amplifier (OP) is an operational amplifier that has 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 resistive elements R1-R2, the capacitive elements D1-D2, and the operational amplifier OP, a second noise cancellation signal is output. The resistive elements R1-R2 and the capacitive elements D1-D2 change in response to the control signals CT-1-CT-4, and the cutoff frequency and phase of the low-pass filter may change. Note that the object of control by the control signal may be not only the cutoff frequency and phase, but also characteristics such as gain. Also, the control signals CT-1-CT-4 may be a common signal with the control signal supplied from the feedback unit 50, or may be signals obtained by adding different bias voltages to a common control signal.

[0043] The first combiner 40 generates a third noise cancellation signal by combining the first noise cancellation signal and the second noise cancellation signal. The third noise cancellation signal is output to the feedback section 50 and the second combiner 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 synthesis unit 40, and feeds back the control signal to the analog unit 30. The analog unit 30 of the present embodiment can change characteristics such as the cutoff frequency, phase, and gain of the above-mentioned low-pass filter based on the control signal.

[0045] The second synthesis unit 60 generates an output signal 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 synthesis unit 60. This allows the user to enjoy only the audio signal, with external noise being cancelled at the user's ear.

[0047] 5A to 5C are block diagrams showing various configuration examples of the feedback section 50 in this embodiment. The feedback section 50 is a circuit that blocks signals having a predetermined frequency component from among input signals. The feedback section 50 can be constructed using 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 section 50 is configured with 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. As with the analog filter 31, the analog filter 51 may be a low-pass filter or the like.

[0050] The level detection circuit 52 includes an integrating 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] 5B, the feedback section 50 is configured with digital circuits, 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 ADC 21, the DSP 22, and the DAC 23 described above.

[0052] The ADC (second A / D conversion circuit) 53 converts 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 converts the filtered digital data into a control signal and outputs it to the analog unit 30.

[0053] In the third configuration example shown in FIG. 5C, the feedback section 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 canceling system 1 in this embodiment. The vertical axis represents volume, and the horizontal axis represents time (seconds). Waveform A is the waveform of the output sound when the ANC function is OFF. Meanwhile, waveform B is the waveform of the output sound when the ANC function is ON. Fig. 6 shows that turning on the ANC function produces a noise canceling effect of 7.8 dB.

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

[0056] As described above, the noise canceling system 1 according to this embodiment feeds back to the analog section 30 a control signal based on the first noise cancellation signal and the second noise cancellation signal from the digital section 20. Therefore, the second noise cancellation signal of the analog section 30 can be dynamically controlled according to the processing of the digital section 20. As a result, it is possible to reduce deterioration of the noise canceling effect caused by the characteristic difference between the digital section 20 and the analog section 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 cutoff frequency, gain, and phase, based on the control signal, thereby improving the noise cancellation effect.

[0058] The analog filter 31 includes a resistive element and a capacitive element, and at least one of the resistance value of the resistive element and the capacitance value of the capacitive element is changed by a control signal, thereby making it possible to change the characteristics of the analog filter 31.

[0059] [Second embodiment] In this embodiment, a modified example of the noise canceling system 1 in the first embodiment will be described. As in the first embodiment, the noise canceling system 2 in this embodiment includes an input section 10, a digital section 20, an analog section 30, a first synthesis section 40, a feedback section 50, a second synthesis section 60, and an output section 70. Since the configuration of each section is almost the same as in the first embodiment, a description of the overlapping parts will be omitted and differences will be described.

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

[0061] That is, the noise canceling system 2 of this embodiment differs from the noise canceling system 1 of the first embodiment in that the feedback section 50 further has a configuration for feeding back a control signal based on the first noise canceling signal and the second noise canceling signal to the digital section 20.

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

[0063] As described above, according to this embodiment, the digital section 20 can change the characteristics of the digital filter in response to the control signal, thereby reducing deterioration of the noise canceling effect caused by the difference in characteristics between the digital section 20 and the analog section 30. Furthermore, the digital section 20 can further improve the noise canceling effect by including an adaptive digital filter that attenuates signal components other than noise based on the control signal.

[0064] [Third embodiment] In this embodiment, a modified example of the noise canceling system 1 in the first embodiment will be described. Since the configurations of the parts with the same reference numerals are almost the same as those in the first embodiment, the description of the overlapping parts will be omitted and only the differences will be described.

[0065] In the first and second embodiments described above, the feedback section 50 generates the control signal based on the 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] 9 is a block diagram showing an example of the overall configuration of the noise canceling system 3 in this embodiment. The noise canceling system 3 in this 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 this embodiment performs filtering and level detection on the difference between the first noise cancellation signal and the second noise cancellation signal, and feeds back a 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 section 30 is controlled so that the difference is small, the difference in the characteristics of the digital section 20 and the analog section 30 can be further reduced. As a result, it is possible to reduce the deterioration of the noise canceling effect caused by the difference in characteristics between the digital section 20 and the analog section 30, and improve the noise canceling effect.

[0068] [Modified embodiment] In the above-mentioned first to third embodiments, a feedback type noise canceling system has been described. However, the present invention can be applied not only to feedback type noise canceling systems, but also to feedforward type noise canceling systems. The noise canceling system may be configured to use both feedforward and feedback types.

[0069] FIG. 10 is a block diagram showing an example of the overall configuration of a noise canceling system 4 in a modified embodiment. The noise canceling system 4 is a feedforward type noise canceling system. The feedforward type 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 not to pick up a signal emitted from a speaker, but to be able to pick up external noise. As a result, the external noise is cancelled at the user's ear, and the user can enjoy only the audio signal.

[0070] The present specification described above is not limited to the above-mentioned embodiment and the attached drawings, and various substitutions, modifications and changes are possible within the scope of the technical idea of ​​the present specification, which is obvious to those who have ordinary knowledge in the technical field to which the present specification belongs. Therefore, the scope of the present specification is indicated by the claims described below, and all modifications or variations derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present specification. [Explanation of symbols]

[0071] 1,2,3,4 Noise Cancelling System 10 Input section 20 Digital Department 21 ADC 22 DSP 23 DAC 30 Analog section 31 Analog Filters 32 Inverting circuit 40 First synthesis section 50 Feedback section 51 Analog Filters 52 Level detection circuit 53 ADC 54 DSP 55 DAC 60 Second synthesis section 70 Output section 80 Subtraction section NS Noise Source S sound source

Claims

1. 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 cancellation signal that is an analog signal; an analog unit that outputs a second noise cancellation signal obtained by filtering the noise signal; a synthesis unit that outputs a third noise cancellation signal obtained by synthesizing 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 cancelling system.

2. the analog section includes a first analog filter; A characteristic of the first analog filter is controlled based on the control signal.

2. The noise cancelling system of claim 1.

3. the first analog filter includes a resistive element and a capacitive element; At least one of the resistance value of the resistive element and the capacitance value of the capacitive element is changed by the control signal.

3. The noise cancelling system of claim 2.

4. the capacitance element is a variable capacitance diode; 4. The noise cancelling system of claim 3.

5. The resistive element is a potentiometer.

4. The noise cancelling system of claim 3.

6. the first analog filter is a low pass filter, The cutoff frequency of the low-pass filter is changed based on the control signal.

3. The noise cancelling system of claim 2.

7. The gain of the first analog filter is varied based on the control signal.

3. The noise cancelling system of claim 2.

8. The phase of the first analog filter is varied based on the control signal.

3. The noise cancelling system of claim 2.

9. the first analog filter is a Bessel filter; 3. The noise cancelling system of claim 2.

10. The feedback unit is a second analog filter for filtering the third noise cancellation signal; and a level detection circuit that detects a level of a signal output from the second analog filter and generates the control signal according to the level; Including, 2. The noise cancelling system of claim 1.

11. The feedback unit is a second A / D conversion circuit that converts the third noise cancellation signal into a second digital signal; a second digital filter circuit for filtering the second digital signal; a second D / A conversion circuit for converting the filtered second digital signal into the control signal; Including, 2. The noise cancelling system of claim 1.

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

2. The noise cancelling system of claim 1.

13. The feedback unit further feeds back the control signal to the digital unit.

2. The noise cancelling system of claim 1.

14. The characteristics of the digital filter circuit of the digital section are controlled based on the control signal converted into a digital signal.

14. The noise cancelling system of 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; 14. The noise cancelling system of claim 13.

16. The control signal is generated based on the third noise cancellation signal.

2. The noise cancelling system of claim 1.

17. The control signal is generated based on a difference between the first noise cancellation signal and the second noise cancellation signal.

2. The noise cancelling system of claim 1.

18. the output section includes a speaker driven by the output signal; The microphone is configured to be capable of collecting the signal emitted from the speaker and the external noise.

2. The noise cancelling system of claim 1.

19. the output section includes a speaker driven by the output signal; The microphone is configured not to pick up the signal emitted from the speaker and to be able to pick up the external noise.

2. The noise cancelling system of 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 cancellation signal that is an analog signal; and an analog unit that outputs a second noise cancellation signal obtained by filtering the noise signal, outputting a third noise cancellation signal obtained by combining the first noise cancellation signal and the second noise cancellation signal; outputting an output signal obtained by adding the third noise cancellation signal to an audio signal from a sound source; feeding back a control signal based on the first noise cancellation signal and the second noise cancellation signal to the analog unit; A method for controlling a noise canceling system comprising:

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