Narrowband cancellation

Abstract

The present disclosure provides a noise-cancellation system (100) and method that generates an anti-noise signal configured to destructively interfere with noise in a cancellation zone (102). The system and method receive a signal representative of the noise in the cancellation zone. The signal is analyzed to identify frequencies to be reduced in the cancellation zone, and the signal is downconverted to place the identified frequencies at baseband. A baseband anti-noise signal is generated based on the downconverted signal. The baseband anti-noise signal is upconverted to the identified frequencies to produce an anti-noise signal having components at the identified frequencies, and the anti-noise signal is provided to be converted into an acoustic signal.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Patent Application Serial No. 62 / 981,315, filed February 25, 2020, entitled “NARROWBANDCAVITY RESONANCE CANCELLATION,” the contents of which are incorporated herein by reference in their entirety for all purposes. Background Technology

[0003] Active acoustic noise cancellation systems generate anti-noise signals that are converted into acoustic signals designed to cancel out unwanted acoustic noise, thereby reducing the unwanted noise. These systems can operate at a very personal level, such as in headphones, or in a broader noise reduction zone, such as in an area close to the user's head. Automotive systems can operate to reduce acoustic noise near the heads of one or more passengers and / or more generally throughout the vehicle interior. Some of these systems may include sensors to detect noise sources and, as in a feedforward system, provide a reference signal associated with the unwanted sound. Various systems include error sensors, such as microphones, to detect acoustic sounds generated in a region of interest and provide an error signal as feedback, allowing the system to be adjusted. Various noise cancellation systems may use one or more reference signals and / or error signals to adjust one or more anti-noise signals converted by various speakers to optimize noise reduction in that area. Summary of the Invention

[0004] The systems and methods disclosed herein relate to audio systems and methods that use one or more microphones to detect narrowband acoustic noise and generate one or more driver signals to be converted by one or more loudspeakers, thereby causing a reduction in the acoustic noise level in the region of the microphone. In various examples, narrowband noise may be associated with resonance in acoustic regions such as wheel cavities (e.g., standing waves within a car wheel) or the vehicle cabin.

[0005] In some examples, the audio system and method of this paper may selectively analyze the microphone signal to detect the presence of narrowband noise (such as that possibly related to resonance) and identify one or more frequency ranges of the frequency, phase, and width of the narrowband noise. In some examples, the frequency ranges in which various resonances or other narrowband noises occur may be known a priori to the system, and the system may analyze the spectrum of the microphone signal to find the resonant peaks within that frequency range. The system uses a portion of the signal near the peak as a feedback signal to actively generate one or more noise-resistant signals.

[0006] According to various aspects, noise cancellation systems and methods are provided that receive a signal representative of noise in a cancellation zone, identify frequencies within the signal to be reduced in the cancellation zone, downconvert the signal to place the identified frequency components at baseband, generate a baseband anti-noise signal based on the downconverted signal, upconvert the baseband anti-noise signal to the identified frequencies to produce an anti-noise signal having components at the identified frequencies, and provide the anti-noise signal to be converted into an acoustic signal.

[0007] In some examples, the signal representative of noise in the cancellation zone is a microphone signal.

[0008] According to various examples, identifying frequencies within the signal to be reduced in the cancellation zone can include analyzing the signal to identify frequencies having peaks in a frequency spectrum of the signal. In certain examples, identifying frequencies within the signal to be reduced in the cancellation zone can include downconverting the signal to baseband and analyzing the downconverted signal to identify one or more peaks in a frequency spectrum of the downconverted signal.

[0009] According to various examples, identifying frequencies within the signal to be reduced in the cancellation zone can include analyzing the signal within a preselected frequency range. In certain examples, the preselected frequency range can be associated with a cavity resonance. Further in particular examples, the cavity resonance can be associated with at least one of a wheel cavity and a vehicle cabin cavity.

[0010] In some examples, the anti-noise signal having components at the identified frequencies is a narrowband anti-noise signal having components at and near the identified frequencies. In various examples, the components at and near the identified frequencies can be limited to a frequency range that is 20 Hz below and 20 Hz above the identified frequencies. In certain examples, the components at and near the identified frequencies are limited to a frequency range that is 10 Hz below and 10 Hz above the identified frequencies.

[0011] According to various examples, the anti-noise signal includes a frequency component having amplitude and phase characteristics that destructively interfere with narrowband noise at or near the identified frequencies.

[0012] Some example noise cancellation systems can include a sensor to provide the signal representative of noise in the cancellation zone. The sensor can be a microphone.

[0013] Some example noise cancellation systems can include a loudspeaker that receives the anti-noise signal and converts the anti-noise signal into an acoustic signal.

[0014] Some example noise cancellation systems can include a controller configured to perform the noise cancellation method. In various examples, the controller can include a processor and a memory.

[0015] These example aspects and other aspects, examples, and advantages of the examples are discussed in further detail below. The examples disclosed herein can be combined with any of the principles disclosed herein in any manner, and the references to “the example,” “some examples,” “an alternative example,” “various examples,” “one example” and the like are not necessarily to the same example. The appearance of the same or similar reference signs in various figures indicates similar or reciprocal aspects unless expressly stated otherwise. BRIEF DESCRIPTION OF DRAWINGS

[0016] Various aspects of at least one example are discussed in detail below with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings are included to provide an illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended as limitations on the claims. In the drawings, like or similar reference signs can be used to indicate like or similar parts throughout the various illustrations. For clarity, not every component can be labeled in every drawing. In the drawings:

[0017] Figure 1 is a schematic diagram of an example noise cancellation system;

[0018] Figure 2 is a schematic block diagram of example operation of the noise cancellation system of Figure 1

[0019] Figure 3 is a schematic block diagram of an example band selector of Figure 2

[0020] Figure 4 is a schematic block diagram of an example control algorithm of Figure 2 DETAILED DESCRIPTION

[0021] Aspects of the disclosure relate to noise cancellation systems and methods that use a microphone to provide a feedback signal and analyze the feedback signal for the presence of narrowband noise within a preselected frequency range. Such narrowband noise can be associated with a resonant noise source. In some examples, the resonant noise source can be associated with an acoustic volume or cavity, such as a wheel cavity (air space within a tire) or a cabin cavity. Such resonant cavities can be pre-determined to produce narrowband resonant noise within one or more frequency ranges.

[0022] ​​​The systems and methods herein are adapted to provide an anti-noise signal for transduction by one or more loudspeakers to interfere with the narrowband noise, thereby reducing the level of the narrowband noise in a listening area. In various examples, the noise-cancellation systems and methods herein can be integrated with various audio systems that also include audio for entertainment, communication, guidance, warning cues, etc. In various examples, the noise-cancellation systems and methods herein can provide the anti-noise signal to a separate audio system for inclusion in various driver signals to the loudspeakers, such as can also include other audio for entertainment, communication, guidance, warning cues, etc.

[0023] Figure 1 is a schematic diagram of an example noise-cancellation system 100. The noise-cancellation system 100 can be configured to destructively interfere with an undesired sound in at least one cancellation zone 102 within a predefined volume 104, such as a vehicle cabin. At a high level, examples of the noise-cancellation system 100 can include one or more microphones 108, one or more loudspeakers 110, and a controller 112. Some examples can include a reference sensor, such as can sense vibrations of one or more components. Some examples can include other reference inputs, such as for receiving information about vehicle speed, engine RPM, torque, etc., such as the controller 112 can determine information from which to analyze a frequency range of narrowband noise in the microphone signals.

[0024] One or more anti-noise signals can be generated by the controller 112 and provided to one or more loudspeakers 110 in the predefined volume, which transduce the anti-noise signals into acoustic energy (i.e., sound waves). The resulting acoustic energy from the anti-noise signals is approximately 180° out of phase with the undesired sound within the cancellation zone 102, and thus destructively interferes with the undesired sound. The combination of the sound waves generated from the anti-noise signals and the undesired noise in the predefined volume results in a reduction of the undesired noise as perceived by a listener in the cancellation zone 102.

[0025] The microphone 108 disposed within the predefined volume generates an error signal based on detecting residual noise (including the undesired noise) in the cancellation zone resulting from the combination of the sound waves. The error signal is provided as feedback to the controller 112, which at least partially represents the residual noise that was not cancelled by the anti-noise signal. The microphone 108 can be, for example, at least one microphone mounted within the vehicle cabin (e.g., the roof, headrest, pillar, or elsewhere within the cabin).

[0026] It should be noted that the cancellation zone can be located remote from the microphone 108. In this case, the error signal can be filtered to represent an estimate of the residual noise in the cancellation zone. In either case, the error signal will be understood to represent the residual undesired noise in the cancellation zone.

[0027] In various examples, the controller 112 can include a non-transitory storage medium 122 and a processor 124. In one example, the non-transitory storage medium 122 can store program code that, when executed by the processor 124, implements the various filters and algorithms described below. The controller 112 can be implemented in hardware and / or software. For example, the controller can be implemented by a SHARC floating point DSP processor, although it should be understood that the controller 112 can be implemented by any other processor, FPGA, ASIC, or other suitable hardware.

[0028] Figure 2 An example operation of the noise cancellation system 100 is shown, including the processing performed by the controller 112. The physical device 210 represents the physical transfer function of the anti-noise signal through the speaker 110, the vehicle interior (e.g., the predetermined volume 104), and the response of the microphone 108. The microphone 108 provides a residual signal 220 produced by the anti-noise signal and the undesired noise in the cancellation zone 102. The residual signal 220 can also be referred to as the microphone signal. The band selector 230 receives the microphone signal and analyzes the signal for narrowband noise in one or more selected frequency ranges. The band selector 230 provides information to the control algorithm 240, and this information identifies one or more frequencies in the microphone signal at which narrowband noise is present. The control algorithm 240 receives the microphone signal and generates an anti-noise signal that is intended to reduce the narrowband noise at each of the one or more identified frequencies. In various examples, the anti-noise signal reduces the narrowband noise in a frequency range around the one or more identified frequencies.

[0029] Figure 3 An example band selector 230 is shown. The band selector can convert the signal to a frequency domain representation, such as via an FFT 232, and find peaks in the frequency spectrum at block 234. The band selector 230 identifies one or more identified frequencies 236 that have such peaks in the frequency spectrum. In some examples, block 234 can only look at selected portions of the frequency spectrum in which narrowband noise can be expected, such as a frequency range in which cavity resonances can be expected. In such examples, block 234 can analyze one or more pre-selected frequency ranges. In various examples, a down conversion can be performed prior to the FFT 232 to move one or more pre-selected frequency ranges to baseband, which can reduce the computational resources required to perform the FFT 232 and find peaks in the frequency spectrum at block 234. Other examples can identify one or more frequencies 236 that have peaks in the frequency spectrum from other narrowband sources (e.g., not necessarily related to cavity resonances). Thus, the frequencies 236 of any narrowband noise can be identified based on peaks in the signal frequency spectrum.

[0030] In some examples, the band selector 230 can operate to identify frequencies in the microphone signal. In other examples, the band selector 230 can also receive a speaker command signal, which represents the anti-noise signal transduced by the speaker. In such examples, block 238 can estimate the original signal at a location, e.g., the acoustic signal present at the location in the absence of the anti-noise signal, e.g., as if the noise cancellation system were not operating. For example, if the noise cancellation system 100 is operating quite well to reduce narrowband noise, so the signal directly from the microphone can not include a peak at the identified frequency, e.g., because the noise cancellation system 100 is effectively reducing the acoustic content at the identified frequency, this can be desirable.

[0031] Figure 4 One example of a control algorithm 240 is shown. The control algorithm 240 receives the identified frequencies 236 from the band selector 230. For each identified frequency, a down-converter 242 down-converts the spectrum of the microphone signal and the speaker command signal at (or near) the identified frequency to baseband. An estimator 244 receives the baseband microphone and speaker command signals and estimates a baseband version of the narrowband noise at the identified frequency (which can be an estimate at a particular location, such as at the location of a passenger’s ear). The estimated baseband noise can be processed through an inverse 246 of the physical device (at baseband), also referred to in some cases as an inverse of the secondary path, to generate a baseband anti-noise signal, which is up-converted by an up-converter 248 to provide the anti-noise signal (which is the speaker command signal).

[0032] Figure 3 And Figure 4 The example band selector 230 and example control algorithm 240 are each merely one example of components of their respective noise cancellation systems 100, and other suitable arrangements exist. Some examples can include one or more adaptive algorithms to adjust the anti-noise signal in response to a feedback (residual) signal from the microphone. For example, the inverse 246 can be implemented as a fixed filter or can be adaptive and “learn” the relationship between the speaker command and the resulting residual signal.

[0033] At least one benefit of the example noise cancellation system 100 and control algorithm 240 is that the described down-conversion to baseband can allow narrowband processing to be implemented with reduced requirements on the number of filter taps. For example, the inverse 246 can be implemented by a filter at baseband with fewer taps to implement the same narrowband operation as operating on the signal at the identified frequency.

[0034] Any suitable hardware and / or software (including firmware, etc.) can be configured to implement or realize the components of the aspects and examples disclosed herein, and various implementations of the aspects and examples can include components and / or functionality beyond those disclosed. Various implementations can include storage instructions for digital signal processors and / or other processing circuitry to cause the circuitry to perform at least in part the functionality described herein.

[0035] Examples disclosed herein can be combined with any of the other examples disclosed herein in any manner consistent with at least one of the principles disclosed herein, and references to “an example,” “some examples,” “an alternate example,” “various examples,” “one example” etc. do not necessarily refer to the same example or to an identical example, but can refer to different or even mutually exclusive examples. It is understood that the examples disclosed herein are only examples and not intended to limit the scope of the application.

[0036] Furthermore, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, components, elements, acts, or functions of the system and method herein indicated as being implemented via a “means” for performing or comprising a “structure” for performing should be understood in

[0037] Having described at least one aspect of at least one example, it will be apparent that modifications and variations are possible without departing from the scope of the disclosure. Such modifications and variations are not to be regarded as a departure from the scope of the application, and applications are intended to be encompassed by the following claims and their equivalents. It is understood that the preceding description and attached drawings are merely exemplary and are therefore specifi cally intended to be only illustrative in nature and not restrictive.

Claims

1. A method of reducing noise, comprising: receiving a signal representing noise in a cancellation zone, wherein the signal representing noise in the cancellation zone is a microphone signal; identifying a frequency within the signal to be reduced in the cancellation zone, wherein the identifying comprises analyzing the signal for the presence of narrowband noise associated with a resonant noise source within a preselected frequency range; downconverting the signal to place the identified frequency at baseband; downconverting a speaker command signal to place the identified frequency at baseband; generating a baseband anti-noise signal based on the downconverted signal and the downconverted speaker command signal; upconverting the baseband anti-noise signal to the identified frequency to produce an anti-noise signal having a component at the identified frequency; and providing the anti-noise signal to be converted into an acoustic signal.

2. The method of claim 1, wherein the preselected frequency range is associated with a cavity resonance.

3. The method of claim 2, wherein the cavity resonance is associated with at least one of a wheel cavity and a vehicle cabin cavity.

4. The method of claim 1, wherein the anti-noise signal having a component at the identified frequency is a narrowband anti-noise signal having components at and near the identified frequency.

5. The method of claim 4, wherein the components at and near the identified frequency are limited to a frequency range 20 Hz below and 20 Hz above the identified frequency, or a narrower range.

6. The method of claim 4, wherein the components at and near the identified frequency are limited to a frequency range 10 Hz below and 10 Hz above the identified frequency, or a narrower range.

7. The method of claim 1, wherein the anti-noise signal includes a frequency component having amplitude and phase characteristics that destructively interfere with narrowband noise at or near the identified frequency.

8. The method of claim 1, wherein identifying a frequency within the signal comprises analyzing the signal to identify a frequency having a peak in a frequency spectrum of the signal.

9. A noise cancellation system, comprising: a sensor configured to provide a signal representing noise in a cancellation zone, wherein the sensor is a microphone and the signal representing noise in the cancellation zone is a microphone signal; and a controller coupled to the sensor and configured to: receive the signal from the sensor, identify a frequency within the signal to be reduced in the cancellation zone, wherein the identifying comprises analyzing the signal for the presence of narrowband noise associated with a resonant noise source within a preselected frequency range, downconvert the signal to place the identified frequency at baseband, downconvert a speaker command signal to place the identified frequency at baseband generate a baseband anti-noise signal based on the downconverted signal and the downconverted speaker command signal, upconvert the baseband anti-noise signal to the identified frequency to produce an anti-noise signal having a component at the identified frequency, and provide the anti-noise signal to be converted into an acoustic signal. The anti-noise signal is provided to be converted into an acoustic signal.

10. The noise cancellation system of claim 9, wherein the preselected frequency range is associated with a cavity resonance.

11. The noise cancellation system of claim 10, wherein the cavity resonance is associated with at least one of a wheel cavity and a vehicle cabin cavity.

12. The noise cancellation system of claim 9, wherein the anti-noise signal having a component at the identified frequency is a narrow-band anti-noise signal having components at and near the identified frequency.

13. The noise cancellation system of claim 12, wherein the components at and near the identified frequency are limited to a frequency range 20 Hz below and 20 Hz above the identified frequency, or a narrower range.

14. The noise cancellation system of claim 12, wherein the components at and near the identified frequency are limited to a frequency range 10 Hz below and 10 Hz above the identified frequency, or a narrower range.

15. The noise cancellation system of claim 9, wherein the anti-noise signal includes a frequency component having amplitude and phase characteristics that destructively interfere with narrow-band noise at or near the identified frequency.

16. The noise cancellation system of claim 9, further comprising a speaker coupled to the controller, the speaker receiving the anti-noise signal and converting the anti-noise signal into an acoustic signal.

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