
{"publication_number": "US-6564184-B1", "abstract": "a digital filter design apparatus for noise suppression by spectral subtraction includes a first spectrum estimator for determining a high frequency resolution noisy speech power spectral density estimate from a noisy speech signal block . a second spectrum estimator determines a high frequency resolution background noise power spectral density estimate from a background noise signal block . averaging units form a piece - wise constant noisy speech power spectral density estimate and a piece - wise constant background noise power spectral density estimate . these averaging units are controlled by devices for adapting the length of individual segments to the shape of the high frequency - resolution noisy speech power spectral density estimate and for using the same segmentation in both piecewise constant estimates . a piece - wise constant digital filter transfer function is determined using spectral subtraction - based on the piece - wise constant noisy speech power spectral density estimate and the piece - wise constant background noise power spectral density estimate .", "application_number": "US-65629500-A", "description": "in some applications the filter is determined in the frequency domain . for example , in telephony applications noise suppression based on spectral subtraction is often used ( see [ 2 , 3 ]). in this case the filter is determined as a function h ( \u03c9 ) of frequency : h \ue89e ( \u03c9 ) = ( 1 - ( \u03b4 \ue89e ( \u03c6 ^ v \ue89e ( \u03c9 ) \u03c6 ^ v \ue89e ( \u03c9 ) ) ) \u03b1 ) \u03b2 where \u03b1 , \u03b2 , \u03b4 are constants and { circumflex over ( \u03c6 )