Patent ID: 9369798
Filing Date: 2016-06-14
CPC Classification: G10K,H04R

Claim Text:
1. A personal audio device, comprising: a personal audio device housing; a transducer mounted on the housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer; at least one microphone mounted on the housing for providing at least one microphone signal indicative of the ambient audio sounds; a delta-sigma modulator for quantizing the at least one microphone signal at an oversampled rate substantially higher than a baseband audio rate of the audio signal; and a processing circuit that generates the anti-noise signal using an adaptive filter operating at the oversampled rate to reduce the presence of the ambient audio sounds heard by the listener in conformity with the at least one microphone signal, wherein a wideband response of an output of the adaptive filter includes a first lowest-frequency image and multiple higher-frequency images at multiples of the oversampled rate, wherein the processing circuit further implements a digital low-pass filter having an input coupled to an the output of the adaptive filter to remove at least some of the higher-frequency images of the quantized microphone signal that appear in the output of the adaptive filter to reduce the dynamic range required by the output of the adaptive filter, and wherein the digital low-pass filter has a corner frequency greater than a maximum frequency of an the first lowest-frequency image in the output of the adaptive filter.