Improved Vector Quantization Approach for Discrete HMM Speech Recognition System

A method and apparatus for monitoring the resonant frequency and absorption level at resonance of an absorption type resonant cavity which involves providing a voltage controlled oscillator, applying to the control input of the voltage controlled oscillator a control signal having a main component Vm and a dither component Vd, splitting the output signal from the voltage controlled oscillator into a portion directed along a test path and a portion directed along a reference path, the reference path including an attenuator controlled by a voltage signal Vk, directing the signal in the test path through the resonant cavity, splitting the signal emerging from the resonant cavity into a portion directed along a frequency detection path and a portion directed along a level detecting path, using the signal directed along the frequency detection path for generating a signal for changing the amplitude of Vm until the center frequency of the output signal of the voltage controlled oscillator is at the resonant frequency fr of the cavity, and using the signal directed along the level detection path for changing Vk until the level of the signal in the reference path is equal to the depth of the null of the signal in the level detection path.

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