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Frequency Measuring

IP.com Disclosure Number: IPCOM000097183D
Original Publication Date: 1962-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Bakis, R: AUTHOR

Abstract

Mean frequency measurement is one technique used in determining formant frequencies for speech recognition. One method for performing this technique is to amplify and clip the speech signal to obtain a series of constant amplitude pulses which are then differentiated, rectified and filtered. A disadvantage of this method is that details of the waveform of the speech signal are removed by the clipper, possibly removing formant information.

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Frequency Measuring

Mean frequency measurement is one technique used in determining formant frequencies for speech recognition. One method for performing this technique is to amplify and clip the speech signal to obtain a series of constant amplitude pulses which are then differentiated, rectified and filtered. A disadvantage of this method is that details of the waveform of the speech signal are removed by the clipper, possibly removing formant information.

This circuit replaces the amplifier and clipper by providing a variable gain amplifier 1 with a square law detector 2 and integrator 3 in the feedback loop. Amplifier 1 with control apparatus 2 and 3 establishes a constant RMS signal independent of variations of the input signal, while still retaining the waveform of the signal. Equalizer 4 is utilized to weight the frequency components of the output signal of amplifier 1. A square law detector 5 determines the level of the signal after weighting. For example, if the equalizer provides a 3db/octave high frequency boost over the entire frequency range, then the output is proportional to the mean frequency.

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