Patent Document ID: 5388182
Application ID: 08017192
Patent Flag: 1

Claim One:
1. A method of encoding acoustic signals for data compression and noise suppression comprising the steps of: (1) utilizing a bank of acoustic filters modeled on the mechanical characteristics of the mammalian cochlea such that the amplitude of the frequency response of the filter in the frequency domain is a smoothed ramp function, also generically referred to as a "shark fin" shape, with tails that guarantee that the acoustic filter is causal because the filter transform function satisfies the Hilbert transform relationships, said filters being established by the substeps comprising: (a) establishing the basic filter function by taking the convolution of a linear ramp filter transfer function frequency response amplitude in the frequency domain with a second function, said ramp function comprising a straight line sloping from zero amplitude at a lower cutoff frequency upward to an upper amplitude at a higher cutoff frequency and having a zero amplitude outside the frequency range from the lower cutoff frequency to the higher cutoff frequency, said second function being a very narrow symmetric single peak distribution so as to produce a ramp function frequency response amplitude with smooth corners such that the response amplitude varies smoothly throughout its frequency range; (b) piecing smooth small amplitude frequency response tails to the said convolution below a second lower cutoff frequency and above a second higher cutoff frequency in such a manner that the frequency response amplitude is continuous and has a defined logarithm for all frequencies and satisfies the Paley-Wiener logarithmic integral condition so that a frequency response phase angle can be ascertained for all frequencies using the Hilbert transform relations, whereby it is assured that the filter is causal; and (c) using the fundamental wavelet relationship to construct a filter bank comprising a plurality of filter impulse responses for a plurality of scales from said basic filter function by scaling said basic filter function according to the wavelet transform relationship, each scale corresponding to a fundamental frequency of a scaled filter, and the entire plurality of scaled filters comprising the filter bank; (2) transforming a finite duration electric signal representing an acoustic signal into a wavelet representation in time and scale of said electric signal by processing the electric signal through the scaled filters in the filter bank; and (3) obtaining the wavelet coefficients ##EQU25## at the zero crossings of the time derivative of the wavelet transform; and (4) truncating the set of wavelet coefficients according to the data capacity and rate of the system to which the coefficients are sent.