Adaptive equalizer preprocessor for mobile telephone speech code

Details Adaptive equalizer preprocessor for mobile telephone speech code Adaptive equalizer preprocessor for mobile telephone speech code

1997-10-17

1999-06-22

Hudspeth, David R.

Data processing: speech signal processing, linguistics, language

Speech signal processing

Recognition

704203, G10L 302

Patent

active

059152354

ABSTRACT:
The present invention teaches an equalizer preprocessor for a mobile telephone speech coder that adapts to the characteristics of its input transducer. The equalizer determines the frequency response of the input transducer by measuring the long term characteristics of the input signal and estimating the spectral envelope of that signal. The equalizer then adapts so that the output signal has a spectral response closer to a perceptually ideal response in accordance with the calculated spectral envelope. In a first embodiment of the present invention, the adaptive equalizer is implemented using digital filtering techniques. The equalizer determines a set of long term autocorrelation coefficient values and from these values generates a set of filter taps which serve to whiten or flatten the spectral response of the input signal. This whitened signal is then passed through a target filter which impresses upon the whitened signal the target spectral response. In an alternative embodiment, the equalizer is realized by using a bank of variable gain control elements to adjust the energy of subbands of the input signal. A subband filter bank divides the input signal into frequency subbands. Each of the subbands is then provided to a corresponding variable gain stage element and the energy of the subband is amplified or reduced depending upon a corresponding subband gain signals. The subband gain signals are determined in accordance with the long term subband energy and a target subband energy.

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