Noise reduction processing arrangement for microphone arrays

Apparatus for processing sounds of the type comprising:

• means for generating a signal defining a preferred location from which to receive wanted sounds;
• receiving means responsive to sounds from the preferred location and unwanted sounds from other changeable locations not including said preferred location for producing signals corresponding to said preferred location sounds and said chrageable location sounds including an array of microphone elements having a prescribed directional response pattern comprising a mainlobe and a plurality of sidelobes separated by minimum response points;
• means for defining successive time intervals, each for analyzing the preferred source sound signals and the plurality of other changeable location unwanted sound signals;
• means for forming a set of weighting signals in each analysis time interval, of the type used to adjust the directional response pattern of the array of microphone elements;
• and
• means for combining the received sound signals with said weighting signals to direct the mainlobe of the array directional response pattern toward the preferred location while directing minimum response points of the array directional response pattern toward the other changeable locations and to produce an output signal substantially representative of the sound signal from the preferred location in each analysis time interval;
• said apparatus being improved in that said weighting signal forming means includes;
• means responsive to the sound signals received from said preferred location and from said other changeable locations in a current analysis time interval for generating a signal representative of the input power of the received sound signals, and a signal representative of the power of an output signal of the current time interval;
• and
• means responsive to the weighting signals of a preceding anaylsis time interval, the current analysis time interval input power signal and the output power signal and the preferred location defining signal for producing a set of weighting signals for the current analysis time interval, including means for calculating from the preceding analysis time interval weighting signals and said defining signal a measure of distortion
• to modify the set of preceding time interval weighting signals according to the following criterion:
• said weighting signal forming means and the combining means iteratively decrease the output power signal towards a minimum while maintaining said calculated measure of distortion at a set value, whereby the result is to maintain the ratio of the output signal power to the power of the input signal of sound from the preferred location substantially at unity over a prescribed frequency range, while decreasing the signals from all other sources.

In a system having a visual monitor, apparatus for processing sound comprising:

• an array of spaced electroacoustic transducers integral with said monitor having a prescribed directional response pattern including a mainlobe and a plurality of sidelobes separated by minimum response points for receiving sound signals from a plurality of sound sources at other locations;
• means for generating a signal defining at least one preferred location sound source relative to said monitor;
• means for generating signals defining successively occurring repetitive sound analysis time intervals;
• means for forming a set of signals for weighting the transducer sound signals in each analysis time interval and;
• means for combining said received sound signals with said set of weighting signals to form an output signal substantially representative of the sound signal from the preferred location sound source in each analysis time interval without regard to silence periods of the sound sources;
• said weighting signal forming means including;
• means responsive to the sound signals received in a current analysis time interval for generating a signal representative of the input power of the received sound signal and a signal representative of the power of an output signal of the current time interval;
• and
• means responsive to the weighting signals of a preceding analysis time interval, the current analysis time interval input power and output power signals and the preferred location defining signal for producing a set of weighting signals for the current analysis time interval to direct the mainlobe of the array directional response pattern toward the sound signal from the preferred location while directing the minimum response points of the prescribed directional response pattern toward the sound signals from other locations, wherein said weighting signal producing means modifies a set of preceding time interval weighting signals in accordance with a calculated measure of distortion limited to a set non-zero value to decrease the aforesaid output power signal toward a minimum, whereby it approximates said signal from said preferred location over a prescribed frequency range.