US-12620400-B2 - Detection and suppression of howl speech signal

US12620400B2US 12620400 B2US12620400 B2US 12620400B2US-12620400-B2

Abstract

A system suppresses howl in a device including microphones and speakers, for example, an artificial reality headset. A speaker of the device presents audio content. The audio content presented by the speaker is received by a microphone of the device thereby creating a howl in certain situations. The system detects the presence of the howl in a region of the audio content using an adaptive notch filter. The system suppresses the howl by reducing gain of one or more frequencies of the audio content. The system may detect presence of the howl by monitoring flatness of the signal. The system may detect presence of the howl based on tonality detection based on linear prediction.

Inventors

Sarmad Aziz Malik
Syavosh ZADISSA
Xiaofei Chen

Assignees

META PLATFORMS TECHNOLOGIES, LLC

Dates

Publication Date: 20260505
Application Date: 20221221

Claims (20)

1 . A computer-implemented method for suppressing howl in a device comprising one or more microphones and one or more speakers, the computer-implemented method comprising: presenting audio content via a speaker of the device; receiving by a microphone of the device, the audio content presented via the speaker; detecting presence of a howl in a region of the audio content using linear prediction to determine a location of an adaptive notch filter; and suppressing the howl in the region of the audio content by reducing gain of one or more frequencies of the howl in the region of the audio content corresponding to the determined location of the adaptive notch filter.
2 . The computer-implemented method of claim 1 , wherein detecting presence of the howl comprises: monitoring flatness of signal; and responsive to detecting more than a threshold flatness of signal, determining that howl is present.
3 . The computer-implemented method of claim 1 , wherein the adaptive notch filter is one of a plurality of adaptive notch filters, wherein the audio content comprises signals of a plurality of frequency ranges, each adaptive notch filter from the plurality of adaptive notch filters associated with a frequency range from the plurality of frequency ranges, wherein the adaptive notch filter is associated with a particular frequency range, wherein suppressing the howl comprises: reducing gain of frequencies of the particular frequency range.
4 . The computer-implemented method of claim 1 , wherein suppressing the howl further comprises: responsive to reducing the gain of the one or more frequencies of the audio content, keeping the gain low for at least a threshold amount of time, thereby eliminating the howl.
5 . The computer-implemented method of claim 4 , further comprising: responsive to eliminating the howl, increasing gain for the one or more frequencies.
6 . The computer-implemented method of claim 1 , wherein the adaptive notch filter has two poles and two zeros.
7 . The computer-implemented method of claim 1 , wherein detecting presence of the howl comprises tonality detection based on the linear prediction.
8 . The computer-implemented method of claim 1 , wherein the device is an artificial reality headset.
9 . A non-transitory computer-readable storage medium storing instructions for suppressing howl in a device comprising one or more microphones and one or more speakers, the instructions when executed by a computer processor, cause the computer processor to perform steps comprising: presenting audio content via a speaker of the device; receiving by a microphone of the device, the audio content presented via the speaker; detecting presence of a howl in a region of the audio content using linear prediction to determine a location of an adaptive notch filter; and suppressing the howl in the region of the audio content by reducing gain of one or more frequencies of the howl in the region of the audio content corresponding to the determined location of the adaptive notch filter.
10 . The non-transitory computer-readable storage medium of claim 9 , wherein instructions for detecting presence of the howl comprise instructions that cause the computer processor to perform steps comprising: monitoring flatness of signal; and responsive to detecting more than a threshold flatness of signal, determining that howl is present.
11 . The non-transitory computer-readable storage medium of claim 9 , wherein the adaptive notch filter is one of a plurality of adaptive notch filters, wherein the audio content comprises signals of a plurality of frequency ranges, each adaptive notch filter from the plurality of adaptive notch filters associated with a frequency range from the plurality of frequency ranges, wherein the adaptive notch filter is associated with a particular frequency range, wherein instructions for suppressing the howl comprise instructions that cause the computer processor to perform steps comprising: reducing gain of frequencies of the particular frequency range.
12 . The non-transitory computer-readable storage medium of claim 9 , wherein instructions for suppressing the howl comprise instructions that cause the computer processor to perform steps comprising: responsive to reducing the gain of the one or more frequencies of the audio content, keeping the gain low for at least a threshold amount of time, thereby eliminating the howl.
13 . The non-transitory computer-readable storage medium of claim 12 , wherein the instructions further cause the computer processor to: responsive to eliminating the howl, increasing gain for the one or more frequencies.
14 . The non-transitory computer-readable storage medium of claim 9 , wherein detecting presence of the howl comprises tonality detection based on the linear prediction.
15 . A device comprising: one or more speakers configured to present audio content via a speaker of the device; one or more microphones configured to receive the audio content presented via the speaker; and a non-transitory computer-readable storage medium storing instructions for suppressing howl in a device comprising one or more microphones and one or more speakers, the instructions when executed by a computer processor, cause the computer processor to perform steps comprising: detecting presence of a howl in a region of the audio content using linear prediction to determine a location of an adaptive notch filter; and suppressing the howl in the region of the audio content by reducing gain of one or more frequencies of the howl in the region of the audio content corresponding to the determined location of the adaptive notch filter.
16 . The device of claim 15 , wherein instructions for detecting presence of the howl comprise instructions that cause the device to perform steps comprising: monitoring flatness of signal; and responsive to detecting more than a threshold flatness of signal, determining that howl is present.
17 . The device of claim 15 , wherein the adaptive notch filter is one of a plurality of adaptive notch filters, wherein the audio content comprises signals of a plurality of frequency ranges, each adaptive notch filter from the plurality of adaptive notch filters associated with a frequency range from the plurality of frequency ranges, wherein the adaptive notch filter is associated with a particular frequency range, wherein instructions for suppressing the howl comprise instructions that cause the computer processor to perform steps comprising: reducing gain of frequencies of the particular frequency range.
18 . The device of claim 15 , wherein instructions for suppressing the howl comprise instructions that cause the computer processor to perform steps comprising: responsive to reducing the gain of the one or more frequencies of the audio content, keeping the gain low for at least a threshold amount of time, thereby eliminating the howl.
19 . The device of claim 18 , wherein the instructions further cause the computer processor to: responsive to eliminating the howl, increasing gain for the one or more frequencies.
20 . The device of claim 15 , wherein detecting presence of the howl comprises tonality detection based on the linear prediction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/357,495, filed on Jun. 30, 2022, which is incorporated by reference in its entirety. FIELD OF THE INVENTION This disclosure relates generally to speech signal processing, and more specifically to a detection and suppression of howling speech signal in devices. BACKGROUND Howl or howling speech signal is formed when there is audio feedback such that an acoustic path exists between an audio input (e.g., microphone) and an audio output (e.g., speaker). For example, a signal received by a microphone is amplified and output by the speaker, and the sound from the loudspeaker again is received by the microphone, amplified, and output by the loudspeaker, and so on. As a result, the system forms a positive feedback loop that results in a howl. The frequency of the resulting howl depends on various factors such as the resonance frequencies of the microphone, amplifier, and speaker. Howl is a problem in conventional wearable devices that include a microphone and speaker that are close to each other. Howl significantly degrades the sound quality of the device and creates a sound that is uncomfortable to the user wearing the device and provides poor user experience. A system may use adaptive feedback cancellers (AFCs) to mitigate howl. However, AFCs only provide stability in a steady state. In the presence of path changes and/or other system variations, an AFC fails to react fast enough to effectively suppress howl. SUMMARY A system, for example, an audio system suppresses howl in a device including microphones and speakers. A speaker of the device presents audio content. The audio content presented by the speaker is received by at least a microphone of the device. This may create a positive feedback loop resulting in a howl. The system detects the presence of the howl in a region of the audio content using an adaptive notch filter. The system suppresses the howl by reducing gain of one or more frequencies of the audio content. According to an embodiment, the system detects presence of the howl by monitoring flatness of the signal. If the system detects more than a threshold flatness of signal, the system determines that howl is present. The system may suppress the howl further by reducing the gain of the one or more frequencies of the audio content and keeping the gain low for at least a threshold amount of time thereby eliminating the howl. Once the howl is eliminated, the system may increase gain for the one or more frequencies again to provide better quality sound. According to an embodiment, the adaptive notch filter is one of multiple adaptive notch filters. The audio content includes signals of multiple frequency ranges. Each adaptive notch filter is associated with a frequency range such that the adaptive notch filter that detects the howl is associated with a particular frequency range. The audio system reduces gain of frequencies of the particular frequency range to reduce the howl. Thereby the system does not reduce gain of all frequencies. According to an embodiment, the system detects presence of the howl based on tonality detection based on linear prediction. According to an embodiment, the device is an artificial reality headset. Embodiments include methods for howl suppression as described herein, systems such as audio systems that implement the methods and computer readable non-transitory storage systems that store instructions for causing a computer system to perform steps of the methods disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a perspective view of a headset 100 implemented as an eyewear device, in accordance with one or more embodiments. FIG. 1B is a perspective view of a headset 105 implemented as an HMD, in accordance with one or more embodiments. FIG. 2 is a block diagram of an audio system 200, in accordance with one or more embodiments. FIG. 3 shows the overall process flow illustrating how the system manages howl according to an embodiment. FIG. 4 illustrates the state machine used by the system to manage howl according to an embodiment. FIG. 5 illustrates a second order adaptive notch filter with two poles and two zeros, according to an embodiment. FIG. 6 illustrates an adaptive graph based on terms of the notch filter, according to an embodiment. FIG. 7 illustrates monitoring of flatness of the signal to determine the howl frequencies according to an embodiment. FIG. 8 illustrates a process for determining howl frequency by measuring flatness of the signal, according to an embodiment. FIG. 9 shows a graph illustrating tonality detection in a sub-band using linear prediction in frequency domain according to an embodiment. FIG. 10 is a system that includes a headset, in accordance with one or more embodiments. The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the follo