Patent US4081607A : Keyword detection in continuous speech using continuous asynchronous correlation

A system for detecting one or more keywords in continuous speech is disclosed wherein a speechprocessor extracts a plurality of analog speech parameters from the input continuous speech, an STV (Spectral Time Vector) generator circuit selectively converts the plurality of analog speech parameters into digitized spectral parameters, an asynchronous correlation circuit continuously correlates sequences of the digitized spectral parameters with stored reference mask templates representative of subelements (dyads or triads) of one or more desired keywords in order to produce continuous correlation data, and a decision function circuit is responsive to the correlation data for developing an occurrence decision output for each desired keyword that is detected.