Method and apparatus for detecting the presence of a speech signal on a voice channel signal

A method for detecting the presence of a speech signal in a voice channel signal, said method providing an active channel indication when said speech signal presence is detected in said voice channel signal and an idle channel indication when the absence of said speech signal presence is detected in said voice channel signal, said voice channel signal being capable of containing both said speech signal and background noise, said speech signal having an envelope associated therewith having a magnitude variable over time, said background noise having an envelope associated therewith having a magnitude substantially constant over time, said voice channel signal having an envelope associated therewith having a magnitude dependent on said magnitudes of said speech signal and said background noise envelopes;

• said method comprising the steps of making a first evaluation of said voice channel signal envelope magnitude over a first time domain to obtain a first resultant output signal, making a second evaluation of said voice channel signal envelope magnitude over a second time domain to obtain a second resultant output signal, said second time domain being different from said first domain, determining the difference in magnitude between said first and second evaluation resultant output signals, comparing said difference with at least a first predetermined value and providing an active channel conditon when said difference exceeds said predetermined value and an idle channel condition when said difference is less than said predetermined value, said active channel indication being provided when said active channel condition is present, said idle channel indication being provided when said idle channel condition is present.

In a system for detecting the presence of a speech signal in a voice channel signal, said system providing an active channel indication when said speech signal presence is detected in said voice channel signal and an idle channel indication when the absence of said speech signal presence is detected in said voice channel signal, said voce channel signal being capable of containing both said speech signal and background noise, said speech signal having an envelope associated therewith having a magnitude variable over time, said background noise having an envelope associated therewith having a magnitude substantially constant over time, said voice channel signal having an envelope associated therewith having a magnitude dependent on said magnitudes of said speech signal and said background noise envelopes;

• said system having first evaluating means for receiving said voice channel signal and evaluating said voice channel signal envelope magnitude over a first time domain for providing a first evaluated output signal, means for providing a first preset threshold level output signal, said first level being preset at a level higher than said background noise envelope magnitude and first comparator means operatively connected to said first preset threshold level providing means and said first evaluating means outputs for comparing the level of said first evaluated output signal with said first preset threshold level and providing an output signal indicative thereof;
• the improvement comprising second evaluating means for making a second evaluation of said voice channel signal envelope magnitude over a second time domain for providing a second evaluated output signal, said second time domain being different from said first time domain;
• second comparator means operatively connected to said first and second evaluating means outputs for comparing said first and second evaluated output signals, determining the difference in magnitude between said first and second evaluated output signals, and comparing said difference with at least a first predetermined value for providing an output signal indicative thereof;
• and condition responsive logic means operatively connected to said first and second comparator means outputs and being responsive thereto for providing a first active channel condition when said first comparator means output signal is indicative of said first evaluated output signal level exceeding said first preset threshold level, a second active channel condition when said second comparator means output signal is indicative of said difference in magnitude between said first and second evaluated output signals exceeding said first predetermined value, and a third idle channel condition when both said first comparator means output signal is indicative of said first evaluated output signal being less than said first preset threshold level and said second comparator means output signal is indicative of said difference in magnitude between said first and second evaluated output signals being less than said first predetermined value, said active channel indication being provided when either said first or second active channel conditions are present, said idle channel indication only being provided when said third idle channel condition is present and neither said first or second active channel conditions is present.