Ultrasound mitigation in wearable devices
A wearable device may include a microphone configured to generate a microphone signal, a speaker configured to be driven by an audio signal, and one or more processors configured to process the microphone signal to determine an amount of ultrasound in the microphone signal; determine, based on the amount of ultrasound, a parameter to control a digital filter that attenuates energy in the microphone signal, in which the digital filter attenuates more when the amount of ultrasound is increasing and less when the amount of ultrasound is decreasing; and apply the digital filter to the microphone signal to generate a reference audio signal that is then processed in a path that produces the audio signal to drive the speaker.
1 . A wearable device, comprising:
a microphone configured to generate a microphone signal;
a speaker configured to be driven by an audio signal; and
one or more processors configured to:
determine an amount of ultrasound in the microphone signal;
dynamically apply a digital filter to the microphone signal to generate a reference audio signal, wherein the digital filter attenuates more energy in the microphone signal when the amount of ultrasound is increasing and attenuates less energy in the microphone signal when the amount of ultrasound is decreasing; and
drive the speaker using the reference audio signal, wherein a path to the speaker includes at least one of a feedforward filter of an acoustic noise cancellation (ANC) subsystem or a transparency filter of a transparency subsystem.
2 . The wearable device of claim 1 , wherein the digital filter attenuates ultrasound energy, or ultrasound-induced energy in an audible range, in the microphone signal to prevent saturation of the audio signal.
3 . The wearable device of claim 1 , wherein the reference audio signal is generated with less delay when less ultrasound is present.
4 . The wearable device of claim 1 , wherein a parameter disables the digital filter, and wherein the reference audio signal is generated with zero delay when no ultrasound is present.
5 . The wearable device of claim 1 , wherein a parameter indicates a weight that controls one or more filter controls of the digital filter.
6 . The wearable device of claim 1 , wherein the digital filter is configured to crossfade between a first filter and a second filter based on the amount of ultrasound.
7 . The wearable device of claim 1 , wherein the digital filter is configured to generate the reference audio signal by combining a first output signal from a first filter with a second output signal from a second filter.
8 . The wearable device of claim 1 , wherein the digital filter comprises a digital biquad filter configured to implement shelf filter.
9 . The wearable device of claim 1 , wherein the digital filter comprises a digital biquad filter configured to implement low pass filter.
10 . The wearable device of claim 1 , wherein the digital filter comprises a digital biquad filter configured to implement one or more notch filters or peak filters with a negative gain in an audible range.
11 . The wearable device of claim 1 , wherein the digital filter is configured to attenuate ultrasound-induced distortion in an audible range.
12 . The wearable device of claim 1 , wherein the microphone, the speaker, and the one or more processors are implemented in a first earbud, and further comprising:
a second earbud in communication with the first earbud, wherein the first earbud and the second earbud synchronize with one another to control the digital filter in each earbud.
13 . The wearable device of claim 1 , wherein the microphone is one of a plurality of microphones that generate a plurality of microphone signals, and the one or more processors determine the amount of ultrasound by determining an envelope of ultrasound for the plurality of microphone signals.
14 . The wearable device of claim 1 , wherein, in response to detecting a decrease in the amount of ultrasound, the digital filter initially maintains an attenuation for a period before reducing the attenuation.
15 . The wearable device of claim 1 , wherein the one or more processors are further configured to:
smooth a transition between more attenuation and less attenuation based on a time constant.
16 . The wearable device of claim 1 , wherein the one or more processors are further configured to:
determine an amount in which a playback signal is masking ultrasound induced distortion in an audible range and controlling the digital filter based on the amount.
17 . The wearable device of claim 1 , wherein the one or more processors are further configured to:
determine an amount in which ambient sound is masking ultrasound induced distortion in an audible range and controlling the digital filter based on the amount.
18 . The wearable device of claim 1 , wherein the digital filter dynamically enables or disables ultrasound filtering based on the amount of ultrasound.
19 . The wearable device of claim 1 , wherein the microphone signal is processed in an ANC mode to generate an ANC signal to destructively interfere with leaked ambient sound.
20 . A method, comprising:
determining an amount of ultrasound in a microphone signal;
dynamically applying a digital filter to the microphone signal to generate a reference audio signal, wherein the digital filter attenuates more energy in the microphone signal when the amount of ultrasound is increasing and attenuates less energy in the microphone signal when the amount of ultrasound is decreasing; and
driving a speaker using the reference audio signal, wherein a path to the speaker includes at least one of a feedforward filter of an acoustic noise cancellation (ANC) subsystem or a transparency filter of a transparency subsystem.