TECHNICAL FIELD

This disclosure generally relates to audio devices. More particularly, the disclosure relates to active noise reduction (ANR) in audio devices.

BACKGROUND

ANR devices can utilize one or more digital signal processors (DSPs) for implementing various signal flow topologies. Examples of such DSPs are described in U.S. Pat. Nos. 10,580,398; 8,073,150; and 8,073,151, each of which is incorporated herein by reference in its entirety.

Conventional feed forward (FF) ANR devices that use fixed controllers (i.e., having a fixed set of filter coefficients) have numerous benefits. For example, these fixed controller-type devices can quickly respond to changes in noise conditions without requiring excessive processing capabilities and/or power consumption. These conventional fixed controller-type ANR devices attempt to approximate an average FF noise response for a group of users. However, such devices can also suffer from performance degradation caused by variations in fit and use by distinct users. In certain form factors, such as in-ear audio devices, variations between users can be significant, thereby contributing to unacceptable performance degradation within a given group of users.

SUMMARY

All examples and features mentioned below can be combined in any technically possible way.

Various aspects include active noise reduction (ANR) devices and related audio devices and approaches for active noise reduction (ANR). In certain cases, the ANR device is gain-adaptive.

In some particular aspects, a method includes: receiving an input signal representing audio captured by a feedforward microphone of an active noise reduction (ANR) headphone; receiving an error signal representing audio captured by an error measurement sensor; generating an anti-noise signal configured to reduce a noise signal over a frequency range; and applying a gain to at least one of the input signal or the anti-noise signal over the frequency range based on the error signal, where the gain is calculated by: filtering the anti-noise signal over the frequency range to generate a filtered feedforward signal, and filtering the error signal over the frequency range to generate a filtered error signal; estimating a feedforward path contribution to the error signal; and determining the gain based on a correlation between the filtered error signal and the filtered feedforward signal with the assigned feedforward path contribution to the error signal.

In some particular aspects, an active noise reduction (ANR) device includes: a feedforward input for receiving an input signal representing audio captured by a feedforward microphone of an active noise reduction (ANR) headphone; a gain control block for receiving an error signal representing audio captured by an error measurement sensor; and an ANR filter for generating an anti-noise signal configured to reduce a noise signal over a frequency range, where the gain control block is configured to apply a gain to at least one of the input signal or the anti-noise signal over the frequency range based on the error signal, where the gain control block calculates the gain by: applying a bandpass filter to the anti-noise signal over the frequency range to generate a filtered feedforward signal, and applying the bandpass filter to the error signal over the frequency range to generate a filtered error signal; estimating a feedforward path contribution to the error signal; and determining the gain based on a correlation between the filtered error signal and the filtered feedforward signal with the assigned feedforward path contribution to the error signal.

Implementations may include one of the following features, or any combination thereof.

In certain implementations, estimating the feedforward path contribution to the error signal is performed with an estimator filter prior to determining the gain.

In particular cases, the estimate of the feedforward path contribution to the error signal is calculated using an estimated system transfer function (Gsd) applied to the anti-noise signal, where the anti-noise signal is generated by an ANR filter.

In some aspects, the estimated system transfer function (Gsd) is an estimate based on measured transfer function components.

In certain implementations, the filtering is performed using a bandpass filter.

In particular cases, the bandpass filter is applied across a frequency range that is predetermined and is equal to approximately 50 Hertz (Hz) to approximately 800 Hz.

In some aspects, a phase of the anti-noise signal and the error signal varies by less than a threshold.

In particular implementations, the method further includes modifying the gain based on at least one of: an overload control adjustment, a self-voice detection adjustment, a music playback mode adjustment, an aware mode adjustment, or a communication mode adjustment.

In certain cases, the anti-noise signal is generated by an ANR filter having a fixed set of filter coefficients for generating the anti-noise signal.

In some aspects, the ANR filter has a voltage limit for generating the anti-noise signal.

In particular cases, the gain has an upper limit based on an expected value of the input signal or the error signal.

In certain implementations, the method further includes: in response to the determined gain exceeding a threshold attributed to a fit of the ANR headphone, sending an indicator to a user of the ANR headphone to adjust the fit.

In some aspects, the method further includes: in response to the determined gain deviating from a threshold attributed to on-head usage of the ANR headphone, at least one of: powering down the ANR headphone or switching the ANR headphone to a standby mode.

In particular cases, the gain is calculated by a gain control block configured to calculate the gain over only the frequency range.

In some aspects, the gain control block down-samples the anti-noise signal and the error signal to mitigate power usage in the ANR headphone.

In particular cases, the error measurement sensor includes a feedback microphone at the ANR headphone, and the method further includes: adjusting, at the ANR filter, the gain based on a feedback signal detected by the feedback microphone.

In certain implementations, the ANR headphone is an in-ear audio device or an around-ear audio device.

In some cases, the ANR device further includes: an estimator filter configured to estimate the feedforward path contribution to the filtered error signal prior to determining the gain, where the estimate of the feedforward path contribution to the filtered error signal is calculated using an estimated system transfer function (Gsd) applied to the anti-noise signal generated by the ANR filter, and the magnitude of the system transfer function (Gsd) is an estimate based on measured transfer function components.

In particular implementations, the gain control block is configured to calculate the gain over only the frequency range and down-sample the anti-noise signal and the error signal to mitigate power usage.

In some aspects, the ANR device further includes a processor coupled with the ANR filter, the processor configured to perform at least one of: a) in response to the determined gain exceeding a threshold attributed to a fit of the ANR headphone, sending an indicator to a user of the ANR headphone to adjust the fit, or b) in response to the determined gain deviating from a threshold attributed to on-head usage of the ANR headphone, at least one of: powering down the ANR headphone or switching the ANR headphone to a standby mode.

Two or more features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects and advantages will be apparent from the description and drawings, and from the claims.

