Adaptive noise reduction filter with low modulation disabling

Details Adaptive noise reduction filter with low modulation disabling Adaptive noise reduction filter with low modulation disabling

1998-05-07

2000-04-25

Isen, Forester W.

Electrical audio signal processing systems and devices

Noise or distortion suppression

Spectral adjustment

381 711, 381 7111, 381 7112, 708322, H04B 1500

Patent

active

060553189

ABSTRACT:
An infinite impulse response (IIR) lowpass filter is placed in the audio path of an audio system wherein the upper cutoff frequency of the filter is adaptively controlled based on a comparison between the average audio signal entering the filter and the average audio signal leaving the filter. An adaptive LMS process is used to control the filter bandwidth so that the average output signal reaches a predefined percentage of the average input signal. An adaptation rate is selected depending on whether the filter bandwidth needs to increase or decrease. Adaptation is fastest for increasing bandwidth and slowest for decreasing filter bandwidth to prevent audible breathing and loss of high frequency information on sudden signal transients. Adaptation is disabled (at least to the extent that decreasing of the filter bandwidth is disabled) whenever low signal modulation is detected.

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