Abstract: A telephone includes at least two microphones and a circuit for processing audio signals coupled to the microphones. The circuit processes the signals, in part, by providing at least one statistic representing maximum normalized cross-correlation of the signals from the microphones, doaEst, dirGain, or diffGain and comparing the at least one statistic with a threshold for that statistic. At least one of noise reduction and speech enhancement is controlled by an indication of near-field sounds in accordance with the comparison. Indication of near-field speech can be further enhanced by combining statistics, including a statistic representing inter-microphone level difference, each of which have their own threshold. dirGain and diffGain are derived from signals incident upon the microphones such that the desired near-field signal is not suppressed.

Abstract: Test apparatus measuring relative frequency response of first and second microphones includes a rotatable carrier. First and second microphones are sealingly clamped against a mounting surface of the carrier aligned with first and second apertures therein, such apertures lying equidistant from, and on opposite sides of, the carrier's axis of rotation. The carrier initially positions the first microphone closest to an audible signal source, and the responses of the microphones to an audible excitation signal are measured. The carrier is rotated 180 degrees, and the measurements are repeated. Elongated strips of gasket material are used to align the microphones and to form a seal with the carrier. When microphones are mounted deep within an audio device, the audio device is sealingly clamped against a mounting plate, sequentially aligning the mounting plate aperture with first and second apertures of the audio device housing corresponding to first and second microphones disposed therein.

Abstract: Test apparatus measuring relative frequency response of first and second microphones includes a rotatable carrier. First and second microphones are sealingly clamped against a mounting surface of the carrier aligned with first and second apertures therein, such apertures lying equidistant from, and on opposite sides of, the carrier's axis of rotation. The carrier initially positions the first microphone closest to an audible signal source, and the responses of the microphones to an audible excitation signal are measured. The carrier is rotated 180 degrees, and the measurements are repeated. Elongated strips of gasket material are used to align the microphones and to form a seal with the carrier. When microphones are mounted deep within an audio device, the audio device is sealingly clamped against a mounting plate, sequentially aligning the mounting plate aperture with first and second apertures of the audio device housing corresponding to first and second microphones disposed therein.

Abstract: Test apparatus measuring relative frequency response of first and second microphones includes a rotatable carrier. First and second microphones are sealingly clamped against a mounting surface of the carrier aligned with first and second apertures therein, such apertures lying equidistant from, and on opposite sides of, the carrier's axis of rotation. The carrier initially positions the first microphone closest to an audible signal source, and the responses of the microphones to an audible excitation signal are measured. The carrier is rotated 180 degrees, and the measurements are repeated. Elongated strips of gasket material are used to align the microphones and to form a seal with the carrier. When microphones are mounted deep within an audio device, the audio device is sealingly clamped against a mounting plate, sequentially aligning the mounting plate aperture with first and second apertures of the audio device housing corresponding to first and second microphones disposed therein.

Abstract: A noise suppression system includes plural microphones, a fixed beam former, a blocking matrix, plural adaptive filters, and a direction of arrival circuit coupled to the adaptive filters that prevents the filters from adapting in the presence of a signal in the look direction. The direction of arrival circuit causes the filters to adapt more quickly in the absence of a signal in the look direction. A pair of adjustable gain circuits is coupled to each microphone. A first adjustable gain circuit from each pair is calibrated during the presence of a desired signal and a second adjustable gain circuit from each pair is calibrated during the presence of an interfering signal. A fixed null-forming circuit is coupled to a first pair of variable gain circuits and an adaptive null forming circuit is coupled to a second pair of adjustable gain circuits. The ratio of the gains of the null forming circuits is used as a control signal.

Abstract: A noise suppression system includes plural microphones, a fixed beam former, a blocking matrix, plural adaptive filters, and a direction of arrival circuit coupled to the adaptive filters that prevents the filters from adapting in the presence of a signal in the look direction. The direction of arrival circuit causes the filters to adapt more quickly in the absence of a signal in the look direction. A pair of adjustable gain circuits is coupled to each microphone. A first adjustable gain circuit from each pair is calibrated during the presence of a desired signal and a second adjustable gain circuit from each pair is calibrated during the presence of an interfering signal. A fixed null-forming circuit is coupled to a first pair of variable gain circuits and an adaptive null forming circuit is coupled to a second pair of adjustable gain circuits. The ratio of the gains of the null forming circuits is used as a control signal.

Abstract: An audio signal is divided among exponentially related subband filters. The spectral flatness measure in each subband signal is determined and the measures are weighted and combined. The sum is compared with a threshold to determine the presence of music or noise. If music is detected, the noise estimation process in the noise reduction circuitry is turned off to avoid distorting the signal. If music is detected, residual echo suppression circuitry is also turned off to avoid inserting comfort noise.

Abstract: A background noise estimate based upon a modified Doblinger noise estimate is used for modulating the output of a pseudo-random phase spectrum generator to produce the comfort noise. The circuit for estimating noise includes a smoothing filter having a slower time constant for updating the noise estimate during noise than during speech. Comfort noise is smoothly inserted by basing the amount of comfort noise on the amount of noise suppression. A discrete inverse Fourier transform converts the comfort noise back to the time domain and overlapping windows eliminate artifacts that may have been produced during processing.

Abstract: In a noise suppresser, an input signal is converted to frequency domain by discrete Fourier analysis and divided into Bark bands. Noise is estimated for each band. The circuit for estimating noise includes a smoothing filter having a slower time constant for updating the noise estimate during noise than during speech. The noise suppresser further includes a circuit to adjust a noise suppression factor inversely proportional to the signal to noise ratio of each frame of the input signal. A noise estimate is subtracted from the signal in each band. A discrete inverse Fourier transform converts the signals back to the time domain and overlapping and combined windows eliminate artifacts that may have been produced during processing.

Abstract: A combination of noise suppression using a Bark band modified Weiner filter and linear noise reduction improves elimination of noise in a telephone. A detector for detecting long, non-speech intervals is coupled to the output of the noise suppresser and controls selection of noise suppression or noise reduction. A gain smoothing filter has a long time constant when noise reduction is used and provides a gradual transition from one level of gain to another. Comfort noise is smoothly inserted by updating the data for generating comfort noise only during detected long, non-speech intervals.

Abstract: A bulk delay estimating circuit matches time intervals representing a signal with time intervals representing an echo of the signal to identify the echo and estimate bulk delay. Bulk delay is estimated by computing (1, 2, . . . n) intervals representing the signal, computing (1, 2, . . . n) intervals representing an echo of the signal, computing absolute differences between corresponding intervals to produce n absolute differences, summing the n absolute differences, and providing an output indicating whether or not the sum is less than a predetermined amount. The intervals are determined by defining a plurality of numbered frames, comparing the energy of a signal during each frame with at least one threshold, storing the numbers of the frames in which the threshold is exceeded, and defining an interval as the period from one frame in which the threshold is exceeded to the next frame in which the threshold is exceeded.

Abstract: A bulk delay estimating circuit correlates time intervals representing a signal with time intervals representing an echo of the signal to identify the echo and estimate bulk delay. Bulk delay is estimated by computing (1, 2, . . . n) intervals representing the signal, computing (1, 2, . . . n) intervals representing an echo of the signal, computing absolute differences between corresponding intervals to produce n absolute differences, summing the n absolute differences, and providing an output indicating whether or not the sum is less than a predetermined amount. The intervals are determined by defining a plurality of numbered frames, comparing the energy of a signal during each frame with at least one threshold, storing the numbers of the frames in which the threshold is exceeded, and defining an interval as the period from one frame in which the threshold is exceeded to the next frame in which the threshold is exceeded.