Detecting a divergence in an adaptive system includes the steps of determining a power of a component of an error signal at a first frequency, the component being correlated to a noise-cancellation signal, the noise-cancellation signal being produced by an adaptive filter and being configured to cancel noise within a predetermined volume when transduced into acoustic signal, wherein the error signal represents a magnitude of a residual noise within the predetermined volume; determining a time gradient of the power of the component of the error signal; and comparing a metric to a threshold, wherein the metric is based, at least in part, on a value of the time gradient of the power of the component of the error signal over a period of time.

An active noise control device includes an updated value table operating unit that writes initial values of an initial value table into an updated value table as updated values and writes updated coefficients of a secondary path filter C{circumflex over ( )} updated in a secondary path filter coefficient updating unit during active noise control, into the updated value table as updated values. The secondary path filter coefficient updating unit reads the updated value corresponding to a frequency from the updated value table before updating the coefficients of the secondary path filter C{circumflex over ( )}, and updates the coefficients of the secondary path filter C{circumflex over ( )}, using the read updated values as the pervious values.

The technology described in this document can be embodied in a method that includes receiving an input signal representing audio captured by a microphone of an active noise reduction (ANR) headphone, processing, by one or more processing devices, a portion of the input signal to determine a noise level in the input signal, and determining that the noise level satisfies a threshold condition. The method also includes, in response to determining that the noise level satisfies the threshold condition, generating an output signal in which ANR processing on the input signal is controlled in accordance with a target loudness level of the output signal, and driving an acoustic transducer of the ANR headphone using the output signal.

A computer-implemented method for determining whether the noise floor of a sensor is deviated from an expected value, comprising the steps of: receiving a sensor signal from a sensor; determining a plurality of power spectral densities from a plurality of successive frames of samples of the sensor signal, each of the plurality of power spectral densities being determined from a respective frame of the plurality of successive frames, each power spectral density being comprised of a plurality of frequency bins, each frequency bin being associated with a power of the respective frame at the frequency of the respective frequency bin, wherein each successive frame of the plurality of successive frames differs by at least one sample; identifying a minimum power of the plurality of power spectral densities; and determining whether the minimum power exceeds a threshold value.

An active noise control unit generates a noise canceling sound of a single frequency that cancels engine sound heard by an occupant and outputs the noise canceling sound to a speaker through an amplifier. A second harmonic detector and a third harmonic detector detect a magnitude of a harmonic component of the noise canceling sound included in sound collected by a microphone. A controller controls a frequency of the noise canceling sound generated by the active noise control unit to a fundamental frequency of the engine sound based on a rotation frequency of the engine, and in addition, causes an output level control unit to control a level of the noise canceling sound to be output to the amplifier so that the level of the noise canceling sound becomes higher when the magnitude of the harmonic component exceeds a predetermined threshold value.

An active noise control device includes an updated value table operating unit that writes initial values of an initial value table into an updated value table as updated values and writes updated coefficients of a secondary path filter C{circumflex over ( )} updated in a secondary path filter coefficient updating unit during active noise control, into the updated value table as updated values. The secondary path filter coefficient updating unit reads the updated value corresponding to a frequency from the updated value table before updating the coefficients of the secondary path filter C{circumflex over ( )}, and updates the coefficients of the secondary path filter C{circumflex over ( )}, using the read updated values as the pervious values.

Sound reduction includes producing an error signal representative of sound present in a target space, producing a reference signal corresponding to undesired sound present in the target space, and producing, based on the reference signal and the error signal a cancelling output signal representative of the undesired sound present in the target space. The method further includes producing, based on the cancelling output signal, sound to destructively interfere with the undesired sound present in the target space, and limiting the amplitude or power of at least one of the reference signal, the error signal and the cancelling output signal if a first condition is met, the at least one signal under examination is at least one of the reference signal, the error signal and the cancelling output signal, and fully or partially suspending the active noise controller update mechanism if a second condition is met.

Adaptive noise cancellation systems and methods comprise a reference sensor operable to sense environmental noise and generate a corresponding reference signal, an error sensor operable to sense noise in a noise cancellation zone and generate a corresponding error signal, a noise cancellation filter operable to receive the reference signal and generate an anti-noise signal to cancel the environmental noise in the cancellation zone, an adaptation module operable to receive the reference signal and the error signal and adaptively adjust the anti-noise signal, and a transient activity detection module operable to receive the reference signal, detect a transient noise event and selectively disable the adaptation module during the detected transient noise event.

An active noise control unit generates a noise canceling sound of a single frequency that cancels engine sound heard by an occupant and outputs the noise canceling sound to a speaker through an amplifier. A second harmonic detector and a third harmonic detector detect a magnitude of a harmonic component of the noise canceling sound included in sound collected by a microphone. A controller controls a frequency of the noise canceling sound generated by the active noise control unit to a fundamental frequency of the engine sound based on a rotation frequency of the engine, and in addition, causes an output level control unit to control a level of the noise canceling sound to be output to the amplifier so that the level of the noise canceling sound becomes higher when the magnitude of the harmonic component exceeds a predetermined threshold value.

A headphone having a speaker, a feedforward microphone, a feedback microphone, and an OED processor. The speaker is configured to transmit an audio playback signal based on a headphone audio signal. The feedforward microphone is configured to sense an ambient noise signal and transmit a feedforward microphone signal based at least in part on the ambient noise signal. The feedback microphone is configured to sense a total audio signal and transmit a feedback microphone signal based at least in part on the total audio signal, in which the total audio signal is the sum of the audio playback signal and at least a portion of the ambient noise level. The OED processor is configured to determine whether the headphone is off ear or on ear, based at least in part on the headphone audio signal, the feedforward microphone signal, and the feedback microphone signal.