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Formant Tracking

IP.com Disclosure Number: IPCOM000097182D
Original Publication Date: 1962-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Bakis, R: AUTHOR

Abstract

This circuit continually adjusts the resonant frequency of a tunable filter to the frequency of an input signal. The circuit is useful for frequency tracking and, particularly, for formant tracking in speech recognition applications.

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Formant Tracking

This circuit continually adjusts the resonant frequency of a tunable filter to the frequency of an input signal. The circuit is useful for frequency tracking and, particularly, for formant tracking in speech recognition applications.

An input signal is applied to fixed band-pass filter 1. This removes undesired frequencies outside the range which the desired frequency is expected to traverse. The signal is then applied to tunable filter 2. The outputs from filters 2 and 1 are applied to a phase discriminator circuit. This includes adder 3, subtractor 4 and 5, and rectifiers 6 and 7. When the input frequency and the resonant frequency of filter 2 differ, a phase difference proportional to the frequency difference occurs.

The phase difference is determined by the phase discriminator circuit which produces a signal proportional to the frequency difference. This signal is fed back to filter 2 through integrator 8 to adjust the resonant frequency of filter 2 to the desired value. An output voltage indicative of the relationship of the resonant frequency with desired value is obtainable at output 9. If the resonant frequency equals the desired one, there is no output from subtractor 5. The output from integrator 8 and, consequently, the feedback signal are constant.

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