Microphone apparatus and headset
View Patent ↗The present invention relates to a microphone apparatus ( 10 ) with a main beamformer (F, BF) that provides a directional audio output (S F ) by combining microphone signals (X, Y) from multiple microphones ( 11, 12 ). The quality of beamformed microphone signals normally depends on the individual microphones having equal sensitivity characteristics across the used frequency range. The invention enables automatic adaptation of the main beamformer (F, BF) to variations in microphone sensitivity and to changes in the alignment of the microphone apparatus ( 10 ) with respect to the user's mouth ( 7 ). This is achieved by having the microphone apparatus ( 10 ): estimate a suppression filter (Z) for an optimum voice-suppression beamformer (Z, BZ) based on the microphone signals (X, Y); estimate a candidate filter (W) for a candidate beamformer (W, BW) as the complex conjugate of the suppression filter (Z); estimate the performance of the candidate beamformer (W, BW); and replace a main filter (F) in the main beamformer (F, BF) with the candidate filter (W) if the candidate beamformer (W, BW) is estimated to perform better than the current main beamformer (F, BF). The invention may be used to enhance speech quality and intelligibility in headsets 1 and other audio devices that pick up user voice.
1. A microphone apparatus configured to provide an output audio signal (S F ) in dependence on voice sound (V) received from a user of the microphone apparatus, the microphone apparatus comprising:
a first microphone unit configured to provide a first input audio signal (X) in dependence on sound received at a first sound inlet;
a second microphone unit configured to provide a second input audio signal (Y) in dependence on sound received at a second sound inlet spatially separated from the first sound inlet;
a linear main filter (F) with a main transfer function (H F ) configured to provide a main filtered audio signal (FY) in dependence on the second input audio signal (Y);
a linear main mixer (BF) configured to provide the output audio signal (S F ) as a beamformed signal in dependence on the first input audio signal (X) and the main filtered audio signal (FY); and
a main filter controller (CF) configured to control the main transfer function (H F ) to increase the relative amount of voice sound (V) in the output audio signal (S F ),
characterized in that the microphone apparatus further comprises:
a linear suppression filter (Z) with a suppression transfer function (Hz) configured to provide a suppression filtered signal (ZY) in dependence on the second input audio signal (Y);
a linear suppression mixer (BZ) configured to provide a suppression beamformer signal (Sz) as a beamformed signal in dependence on the first input audio signal (X) and the suppression filtered signal (ZY);
a suppression filter controller (CZ) configured to control the suppression transfer function (Hz) to minimize the suppression beamformer signal (S Z );
a linear candidate filter (W) with a candidate transfer function (Hw) configured to provide a candidate filtered signal (WY) in dependence on the second input audio signal (Y);
a linear candidate mixer (BW) configured to provide a candidate beamformer signal (S W ) as a beamformed signal in dependence on the first input audio signal (X) and the candidate filtered signal (WY);
a candidate filter controller (CW) configured to control the candidate transfer function (Hw) to be congruent with the complex conjugate of the suppression transfer function (H Z ); and
a candidate voice detector (AW) configured to use a voice measure function (A) to determine a candidate voice activity measure (Vw) of voice sound (V) in the candidate beamformer signal (Sw), and in that the main filter controller (CF) further is configured to control the main transfer function (H F ) to converge towards being congruent with the candidate transfer function (Hw) in dependence on the candidate voice activity measure (Vw).
2. A microphone apparatus according to claim 1 , wherein the suppression filter controller (CZ) further is configured to:
accumulate a first auto-power spectrum (Pxx) based on the first input audio signal (X);
accumulate a second auto-power spectrum (Pyy) based on the second input audio signal (Y);
accumulate a first cross-power spectrum (Pxy) based on the first input audio signal (X) and the second input audio signal (Y); and
control the suppression transfer function (Hz) based on the first auto-power spectrum (Pxx), the second auto-power spectrum (Pyy) and the first cross-power spectrum (Pxy).
3. A microphone apparatus according to claim 2 , wherein the suppression filter controller (CZ) further is configured to control the suppression transfer function (Hz) using a finite impulse response Wiener filter computation based on the first auto-power spectrum (Pxx), the second auto-power spectrum (Pyy) and the first cross-power spectrum (Pxy).
4. A microphone apparatus according to claim 1 , and further comprising a residual voice detector (AZ) configured to use the voice measure function (A) to determine a residual voice activity measure (Vz) of voice sound (V) in the suppression beamformer signal (Sz), and wherein the main filter controller (CF) further is configured to control the main transfer function (H F ) to converge towards being congruent with the candidate transfer function (Hw) in dependence on the candidate voice activity measure (Vw) and the residual voice activity measure (Vz).
5. A microphone apparatus according to claim 4 , wherein the main filter controller (CF) further is configured to:
determine a candidate beamformer score (E) in dependence on the candidate voice activity measure (Vw) and the residual voice activity measure (V Z );
control the main transfer function (H F ) in further dependence on the candidate beamformer score (E) exceeding a first threshold (E B ); and
increase the first threshold (E B ) in dependence on the candidate beamformer score (E).
6. A microphone apparatus according to claim 5 , wherein the main filter controller (CF) further is configured to provide a user-voice activity signal (VAD) in dependence on a beamformer score (E, E F ) exceeding a second threshold (Ev).
7. A microphone apparatus according to claim 6 , wherein the main filter controller (CF) further is configured to provide a no-user-voice activity signal (NVAD) in dependence on a beamformer score (E, E F ) not exceeding a third threshold (E N ), wherein the third threshold (E N ) is lower than the second threshold (Ev).
8. A microphone apparatus according to claim 1 , wherein the voice measure function (A) correlates positively with an energy level or an amplitude of a signal (S W , Sz) to which it is applied.
9. A microphone apparatus according to claim 1 , wherein the first microphone unit comprises a first delay unit configured to delay the first input audio signal (X) and/or the second microphone unit comprises a second delay unit adapted to delay the second input audio signal (Y).
10. A headset ( 1 ) comprising a microphone apparatus ( 10 ) according to claim 1 .