Apparatus And A Method For Audio Signal Processing

Abstract

An apparatus, such as a headset, configured to process audio signals from multiple microphones, comprising: a first pair of microphones ( 101, 102 ) outputting a first pair of microphone signals and a second pair of microphones ( 103, 104 ) outputting a second pair of microphone signals; a first beamformer ( 105 ) and a second beamformer ( 106 ) each configured to receive a pair of microphone signals and adapt the spatial sensitivity of a respective pair of microphones as measured in a respective beamformed signal (X L ; X R ) output from a respective beamformer ( 105; 106 ); wherein the spatial sensitivity is adapted to suppress noise relative to a desired signal; a third beamformer ( 107 ) configured to dynamically combine the signals (X L ; X R ) output from the first beamformer ( 105 ) and the second beamformer ( 106 ) into a combined signal (X C ); wherein the signals are combined such that signal energy in the combined signal is minimized while a desired signal is preserved; and a noise reduction unit ( 109 ) configured to process the combined signal (X C ) from the third beamformer ( 107 ) and output the combined signal such that noise is reduced.

1 . An apparatus, such as a headset, configured to process audio signals from multiple microphones, comprising:
 a first pair of microphones outputting a first pair of microphone signals and a second pair of microphones outputting a second pair of microphone signals; wherein the first pair of microphones are arranged with a first mutual distance and the second pair of microphones are arranged with a second mutual distance, and wherein the first pair of microphones are arranged at a distance from the second pair of microphones that is greater than the first mutual distance and the second mutual distance at least when the apparatus is in normal operation;   a first beamformer and a second beamformer each configured to receive a pair of microphone signals and adapt the spatial sensitivity of a respective pair of microphones as measured in a respective beamformed signal (X L ; X R ) output from a respective beamformer; wherein the spatial sensitivity is adapted to suppress noise relative to a desired signal;   a third beamformer configured to dynamically combine the signals (X L ; X R ) output from the first beamformer and the second beamformer into a combined signal (X C ); wherein the signals are combined such that noise energy in the combined signal is minimized while a desired signal is preserved;   a noise reduction unit configured to process the combined signal (X C ) from the third beamformer and output the combined signal such that noise is reduced.   
     
     
         2 . An apparatus according to  claim 1 ,
 wherein the noise reduction unit is configured to perform noise suppression on the combined signal (X C ) from the third beamformer in response to a noise suppression coefficient (A L ; A R ); and   wherein the noise suppression coefficient (A L ; A R ) is estimated from the microphone signals and/or a beamformed signal (X L ; X R ).   
     
     
         3 . An apparatus according to  claim 1 , wherein the apparatus comprises:
 a first control branch synthesizing a first noise suppression gain, A L , from the first pair of microphone signals and/or the first beamformer;   a second control branch synthesizing a second noise suppression gain, A R , from the second pair of microphone signals and/or the second beamformer;   a selector configured to dynamically select and/or output the first noise suppression gain, A L , or the second noise suppression gain, A R ;   
       wherein the noise reduction unit is configured to process the combined signal from the third beamformer in response to the selected and/or output noise suppression gain, A S , from the selector. 
     
     
         4 . An apparatus according to  claim 3 ,
 wherein the selector is configured to operate in response to a first signal quality indicator (P L ) and a second signal quality indicator (P R ); and   wherein the signal quality indicators (P L ; P R ) are synthesized from a respective beamformed signal (X L ; X R ) processed to reduce noise in response to respective noise reduction gains (A L ; A R ).   
     
     
         5 . An apparatus according to  claim 3 ,
 wherein a beamformed signal (X L ; X R ), processed to reduce noise in response to respective noise reduction gains (A L ; A R ), is input to an evaluator that is configured to output a control signal (P L ; P R ) to the selector and thereby control selection; and   wherein the evaluator evaluates the beamformed signal (X L ; X R ), processed to reduce noise in response to respective noise reduction gains (A L ; A R ), according to a criterion of least power during a time interval when voice activity is detected as not present.   
     
     
         6 . An apparatus according to  claim 2 , wherein the noise suppression coefficient is computed to reduce noise by a predetermined, fixed factor. 
     
     
         7 . An apparatus according to  claim 1 , wherein at least one of the first beamformer or second beamformer is configured to comprise:
 a first stage that generates a summation signal and a difference signal from the input signals, subject to at least one of the input signals being phase and/or amplitude aligned with another of the input signals with respect to a desired signal; and   a second stage that filters the difference signal and generating a filtered signal;   wherein the beamformed output signal is generated from the difference between the summation signal and the filtered signal; and   wherein the filter is adapted using a least mean square technique to minimize the power of the beamformed output signal.   
     
     
         8 . An apparatus according to  claim 1 , wherein the third beamformer is configured with a fixed sensitivity with respect to a predefined spatial position relative to the spatial position of the microphones. 
     
     
         9 . An apparatus according to  claim 1 , wherein the microphones output digital signals;
 wherein the apparatus performs a transformation of the digital signals to a time-frequency representation, in multiple frequency bands; and   wherein the apparatus performs an inverse transformation of at least the combined signal to a time-domain representation.   
     
     
         10 . An apparatus according to  claim 1 , wherein the microphones output analogue signals;
 wherein the apparatus performs analogue-to-digital conversion of the analogue signals to provide digital signals;   wherein the apparatus performs a transformation of the digital signals to a time-frequency representation, in multiple frequency bands; and   wherein the apparatus performs an inverse transformation of at least the combined signal to a time-domain representation.   
     
     
         11 . An apparatus according to  claim 1 , wherein the microphones of at least one pair of the set of microphones is arranged in an end-fire configuration oriented towards a position where a person's mouth is expected to be when the apparatus is used by the person. 
     
     
         12 . A method for processing audio signals from multiple microphones, comprising:
 receiving a first pair and a second pair of microphone signals from a first pair of microphones and a second pair of microphones, respectively; wherein the first pair of microphones are arranged with a first mutual distance and the second pair of microphones are arranged with a second mutual distance, and wherein the first pair of microphones are arranged at a distance from the second pair of microphones that is greater than the first mutual distance and the second mutual distance at least when the apparatus is in normal operation;   performing first beamforming and second beamforming on the first pair of microphone signals and the second pair of microphone signals to output respective beamformed signals (X L ; X R );   adapting the spatial sensitivity by a respective pair of microphones as measured in a respective beamformed signal (X L ; X R ) such that spatial sensitivity is adapted to suppress noise relative to a desired signal;   performing third beamforming to dynamically combine the signals (X L ; X R ) output from the first beamforming and the second beamforming into a combined signal (X C ); wherein the signals are combined such that noise energy in the combined signal is minimized while a desired signal is preserved;   performing noise reduction to process the combined signal (X C ) from the third beamformer and output the combined signal such that noise is reduced.   
     
     
         13 . A computer program product comprising program code means adapted to cause a data processing system to perform the steps of the method according to  claim 12 , when said program code means are executed on the data processing system. 
     
     
         14 . A computer program product according to  claim 13 , comprising a computer-readable medium having stored thereon the program code means. 
     
     
         15 . A computer data signal embodied in a carrier wave and representing sequences of instructions which, when executed by a processor, cause the processor to perform the steps of the method according to  claim 12 .