# US 10,319,361 B2 · Digital circuit arrangements for ambient noise-reduction

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- Number: US 10,319,361 B2
- Document ID: US10319361B2
- Status: Granted
- Kind: B2
- Application number: 15/383,839
- Filed: 2016-12-19
- Published: 2017-04-13
- Granted: 2019-06-11
- Earliest claimed: 2012-03-09
- Assignees: Cirrus Logic, Inc.
- Applicants: Cirrus Logic International Semiconductor Ltd.
- Inventors: Richard Clemow
- Web page: https://patentgrep.com/patent/US10319361B2

## CPC

- H04R 1/1083: {Reduction of ambient noise (active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06)}
- G10K 11/16: Methods or devices for protecting against, or for damping, noise or other acoustic waves in general (G10K11/36 takes precedence)
- G10K 11/178: by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K 11/17853: {of the filter}
- G10K 11/17855: {for improving speed or power requirements}
- G10K 11/17873: {using a reference signal without an error signal, e.g. pure feedforward}
- G10K 11/17875: {using an error signal without a reference signal, e.g. pure feedback}
- G10K 11/17885: {additionally using a desired external signal, e.g. pass-through audio such as music or speech}
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- G10K 2210/1081: Earphones, e.g. for telephones, ear protectors or headsets
- G10K 2210/3051: Sampling, e.g. variable rate, synchronous, decimated or interpolated
- G10K 2210/3217: Collocated sensor and cancelling actuator, e.g. "virtual earth" designs
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)
- G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR

## Abstract

A digital circuit arrangement for an ambient noise-reduction system affording a higher degree of noise reduction than has hitherto been possible. The arrangement converts the analog signals into N-bit digital signals at sample rate f0, and then subjects the converted signals to digital filtering. The value of N in some embodiments is 1 but, in any event, is no greater than 8, and f0 may be 64 times the Nyquist sampling rate but, in any event, is substantially greater than the Nyquist sampling rate. This permits digital processing to be used without incurring group delay problems that rule out the use of conventional digital processing in this context. Furthermore, adjustment of the group delay can readily be achieved, in units of a fraction of a micro-second, providing the ability to fine tune the group delay for feed forward applications.

## Claims

### Claim 1

A listening device, comprising:
a loudspeaker, positioned to direct sound in a forward direction towards a listener;
a microphone, positioned in front of the loudspeaker, to detect sounds generated by the loudspeaker and ambient noise reaching the listener, wherein the microphone is adapted to generate an analog signal; and
a noise reduction processing system, for generating a noise reduction output signal to be applied to the loudspeaker, in response to the analog signal, the system comprising:
an input, for receiving the analog signal;
an analog-digital converter, for generating a digital signal from the analog signal representing ambient noise;
a decimating filter, for generating a decimated digital signal from the digital signal generated by the analog-digital converter;
a digital signal processing filter, for receiving the decimated digital signal as an input, for filtering the decimated digital signal, and for outputting the filtered decimated digital signal as a noise cancellation signal;
an interpolating filter, for generating an interpolated noise cancellation signal from the noise cancellation signal; and
a digital-analog converter for generating an output noise cancellation signal from the interpolated noise cancellation signal,
wherein the digital-analog converter is coupled to the loudspeaker in order to supply the output noise cancellation signal to the loudspeaker.

### Claim 2 (depends on 1)

A listening device according to claim 1, wherein the decimating filter comprises:
a low-pass filter; and
a downsampler.

### Claim 3 (depends on 1)

A listening device according to claim 1, wherein the interpolator comprises:
an upsampler; and
a low-pass filter.

### Claim 4 (depends on 1)

A listening device according to claim 1, wherein the analog-digital converter comprises a delta-sigma modulator.

### Claim 5 (depends on 1)

A listening device according to claim 1, wherein the digital-analog converter comprises a delta-sigma modulator.

### Claim 6 (depends on 5)

A listening device according to claim 5, wherein the digital-analog converter further comprises a 1-bit digital-analog converter connected to an output of the delta-sigma modulator.