Method and apparatus for cancelling room reverberation and noise pickup

A method of generating nonreverberant sound signals adapted for monaural operation comprising the steps of:

• receiving a signal x(t) of a first microphone and a signal y(t) of a second microphone which is spatially separated from said first microphone;
• converting said x(t) signal to a frequency domain signal X(.omega.) and said y(t) signal to a frequency domain signal Y(.omega.);
• multiplying said frequency domain signal X(.omega.) by a unity magnitude phasor A(.omega.) having a phase angle at each frequency .omega. equal to the phase angle difference at said frequency .omega. between said X(.omega.) and Y(.omega.) signals to form a product signal A(.omega.)X(.omega.);
• adding to each frequency element of said Y(.omega.) signal corresponding frequency elements of said A(.omega.)X(.omega.) signal to form a co-phased and added signal;
• multiplying said co-phased and added signal by a gain factor related to the cross-spectrum function R.sub.xy (.omega.) of the component signals X(.omega.) and Y(.omega.) to form a gain factor multiplied signal;
• and
• converting said gain factor multiplied signal to form a single nonreverberant time domain signal.

A method for generating nonreverberant sound signals from a sound source located in a reverberant room comprising the steps of:

• receiving a signal x(t) of a first microphone and a signal y(t) of a second microphone which is spatially separated from said first microphone;
• sampling said x(t) and y(t) signals at D second intervals to form sampled signals x(nD) and y(nD), where n is a running variable;
• forming short-term Fourier spectra signals X(mF) and Y(mF) of signals x(nD) and y(nD), respectively, where F is a frequency spacing and m is a running variable;
• multiplying said X(mF) spectrum signal by a phasor signal A(mF) having a phase angle at each frequency element mF equal to the phase angle difference between X(mF) and Y(mF) signals, forming thereby a product signal A(mF)X(mF);
• adding said Y(mF) signal to said product signal A(mF)X(mF) to form a co-phased and added signal;
• multiplying said co-phased and added signal by a gain factor related to the cross-spectrum function of said X(mF) and Y(mF) signals to form a gain factor multiplied signal;
• and
• combining said gain factor multiplied signal to form a single nonreverberant time domain signal.

A method for generating a nonreverberant signal in response to sounds generated in a reverberant room comprising the steps of:

• receiving a signal x(t) from a first microphone located in said reverberant room and a signal y(t) from a second microphone located in said reverberant room, said second microphone being spatially separated from said first microphone;
• low-pass filtering of said x(t) and y(t) received signals;
• sampling at D second intervals said x(t) and y(t) signals to form signal sequences x(nD) and y(nD);
• low-pass filtering said x(nD) and y(nD) sampled signals;
• transforming to frequency domain successive fixed length subsequences of said x(nD) and y(nD) sequences;
• multiplying the transformed signal of said x(nD) sequence by a unity magnitude phasor whose angle is proportional to the cross-spectrum function of said transformed signals;
• adding the transformed signal of said y(nD) sequence to the phasor multiplied signal of said step of multiplying the transformed signal of said x(nD) sequence;
• multiplying the output signal developed by said step of adding with a gain control factor proportional to the normalized average magnitude of said cross-spectrum function;
• and
• transforming to time domain the signals developed by said step of multiplying with a gain factor.

A reverberation reduction apparatus responsive to a first signal developed by a first signal pick-up device and a second signal developed by a second signal pick-up device comprising:

• an all-pass filter for imparting a phase angle to said first signal in accordance with a delay control signal;
• first processor means responsive to said first and second signals for developing said delay control signal in proportion to the angle of the cross-spectrum of said first and second signals;
• adder means for combining said second signal with the output signal of said all-pass filter;
• second processor means responsive to said first and second signals for developing a gain control signal proportional to an averaged magnitude of the cross-spectrum of said first and second signals;
• and
• gain control means for modifying the output signal of said adder means in response to said gain control signal.

Apparatus for developing a nonreverberant noise free signal in response to sounds developed in a room capable of sustaining uncorrelated signals comprising:

• a first signal pick-up means;
• a second signal pick-up means in spatial proximity to said first signal pick-up means;
• means for subdividing the signal generated by said first pick-up means into narrow frequency bands;
• means for subdividing the signal generated by said second pick-up means into narrow frequency bands corresponding to said narrow frequency bands of said first pick-up means;
• means for combining said corresponding narrow frequency bands of said first and second pick-up means under control of a delay determining signal, to form combined narrow frequency bands;
• means for modifying the amplitude of said combined narrow frequency bands under control with a gain determining signal;
• and
• processor means responsive to said narrow frequency bands of said first pick-up means and to said narrow frequency bands of said second pick-up means for developing said delay determining signal and said gain determining signal.

Apparatus for developing a nonreverberant signal including a first microphone and a second microphone, both situated in a reverberant room and in proximity to one another comprising:

• first means for sampling the output signals of said first microphone and said second microphone to develop sampled signals x(nD) and y(nD). respectively;
• second means for transforming successive and overlapping fixed length sequences of said x(nD) and y(nD) signals into the frequency domain to form signals X(mF,kT) and Y(mF,kT), respectively;
• third means for combining said X(mF,kT) and Y(mF,kT) signals to form co-phased and added signals;
• fourth means for modifying the gain of said co-phased and added signals to form a gain modified signal;
• and
• fifth means for transforming said gain modified signal to a nonreverberant time sample sequence.

Apparatus for developing a nonreverberant signal in response to sounds produced in a reverberant room, including a first sound pick-up device developing a first input signal and a second sound pick-up device developing a second input signal comprising:

• first processor means for developing sample sequences of successive and overlapping fixed length segments of said first input signal;
• second processor means for developing frequency sample sequences of successive and overlapping fixed length segments of said second input signal which correspond to said successive and overlapping fixed length segments of said first input signal;
• third processor means for combining said frequency sample sequences of said first and second processor means;
• and
• fourth processor means responsive to said third processor means for developing said nonreverberant signal.

A method for generating nonreverberant sound signals adapted for monaural operation comprising the steps of:

• receiving the signals of a first signal pick-up device and of a second signal pick-up device which is spatially separated from said first signal pick-up device;
• separating the signals of said first and second pick-up devices into a plurality of frequency band signals;
• multiplying each frequency band signal of said first pick-up device by a unity magnitude phasor having a phase angle equal to the phase angle difference between each frequency band signal of said first pick-up device and a corresponding frequency band signal of said second pick-up device;
• adding to each of said multiplied frequency band signals of said first pick-up device said corresponding frequency band signals of said second pick-up device to form a plurality of combined frequency band signals;
• multiplying each of said combined frequency band signals by a gain factor related to the late echo affects in the frequency band signals forming each of said combined frequency band signals, to form gain factor multiplied frequency band signals;
• and
• combining the gain factor multiplied frequency band signals of said step of multiplying each of said combined frequency band signals to form a single nonreverberant signal.

A reverberation reduction apparatus responsive to a first signal developed by a first signal pick-up device and a second signal developed by a second signal pick-up device comprising:

• an all-pass filter for imparting a phase angle to said first signal in accordance with a delay control signal;
• first processor means responsive to said first and second signals for developing said delay control signal in proportion to the angle of the cross-spectrum of said first and second signals;
• adder means for combining said second signal with the output signal of said all-pass filter;
• second processor means responsive to said first and second signals for developing a gain control signal related to the cross-spectrum of said first and second signals;
• and
• gain control means for modifying the output signal of said adder means in response to said gain control signal.