Voice Detection and Discrimination
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
This invention relates to the dynamic detection and discrimination between voiced and ringback signals in a telephone system. Ringback signals have characteristic 440 and 480 Hertz spectral peaks, whereas voiced signals consist of three or more frequencies. Responsive to a signal's presence, a signal is treated as voiced if it is not the spectral twin of the ringback signal. A cascade of feed forward comparison networks implements the detector and discriminator. Fig. 1 shows the ringback detector circuit, and Fig. 2 shows the second part of the voice detection circuit. In the ringback detector circuit all signals are bandpassed to between 350 and 600 Hertz. Because of the formant frequency characteristics of voice, a signal will always be available at the output of the bandpass filter whenever voice occurs.