Audio signal processing method and system for echo mitigation using an echo reference derived from an internal sensor

An audio system comprising at least an internal sensor, an external sensor and a speaker unit, wherein the internal sensor is arranged to measure voice acoustic signals emitted by a user of the audio system which reach the internal sensor by propagating internally to a head of the user and the external sensor is arranged to measure voice acoustic signals emitted by the user which reach the external sensor by propagating externally to the user's head, wherein the internal sensor and the external sensor are configured to produce an internal audio signal and an external audio signal by measuring simultaneously acoustic signals reaching the internal sensor and acoustic signals reaching the external sensor, respectively, wherein said audio system further comprises a processing circuit configured to:

• convert the internal audio signal to frequency domain, thereby producing an internal audio spectrum, wherein the audio system is an earbud or headphone device,
• convert the external audio signal to frequency domain, thereby producing an external audio spectrum,
• estimate, based on the internal audio spectrum, an echo audio spectrum of an echo audio signal caused by the speaker unit in the external audio signal, wherein the echo audio spectrum is estimated for frequencies above a minimum frequency, wherein the minimum frequency is greater than or equal to 600 hertz, and wherein the internal audio spectrum, the external audio spectrum and the echo audio spectrum are complex spectra,
• correct the external audio spectrum for frequencies above the minimum frequency, based on the echo audio spectrum, including subtracting the echo audio spectrum from the external audio spectrum for frequencies above the minimum frequency, and
• combining the corrected external audio spectrum with the internal audio spectrum to produce an output audio spectrum.

A non-transitory computer readable medium comprising computer readable code to be executed by an audio system comprising at least an internal sensor, an external sensor and a speaker unit, wherein the internal sensor is arranged to measure voice acoustic signals emitted by a user of the audio system which reach the internal sensor by propagating internally to a head of the user and the external sensor is arranged to measure voice acoustic signals emitted by the user which reach the external sensor by propagating externally to the user's head, wherein said audio system further comprises a processing circuit, wherein said computer readable code causes said audio system to:

• produce an internal audio signal and an external audio signal by measuring simultaneously acoustic signals reaching the internal sensor and acoustic signals reaching the external sensor, respectively, wherein the audio system is an earbud or headphone device,
• convert the internal audio signal to frequency domain, thereby producing an internal audio spectrum,
• convert the external audio signal to frequency domain, thereby producing an external audio spectrum,
• estimate, based on the internal audio spectrum, an echo audio spectrum of an echo audio signal caused by the speaker unit in the external audio signal, wherein the echo audio spectrum is estimated for frequencies above a minimum frequency, wherein the minimum frequency is greater than or equal to 600 hertz, and wherein the internal audio spectrum, the external audio spectrum and the echo audio spectrum are complex spectra,
• correct the external audio spectrum for frequencies above the minimum frequency, based on the echo audio spectrum, including subtracting the echo audio spectrum from the external audio spectrum for frequencies above the minimum frequency, and
• combining the corrected external audio spectrum with the internal audio spectrum to produce an output audio spectrum.