1. A method for processing speech signals, comprising operations of: applying a primary transformation to a digital input speech signal to extract primary features therefrom; applying each of at least one secondary transformation to one of the input speech signal and the primary features to yield secondary features statistically dependant on the primary features; applying at least one predetermined function to form a combined signal comprising a combination of the primary features with the secondary features; generating a recognition answer by pattern matching the combined signal against predetermined voice recognition templates.