1. In a speech recognition apparatus wherein speech units are each characterized by a sequence of template patterns, and having means for processing a speech input signal for repetitively deriving therefrom, at a frame repetition rate, a plurality of speech recognition acoustic parameters, and means responsive to said acoustic parameters for generating likelihood costs between said acoustic parameters and said speech template patterns, and for processing said likelihood costs for determining the speech units in said speech input signal, the method for generating said acoustic parameters comprising the steps of digitally sampling said speech input signal, processing said sampled signal for repetitively determining the discrete spectrum of time windowed durations of said signal, at a selected plurality of frequencies, said spectrum values corresponding to a vector of parameter components, reducing the number of parameter components, in said vector by performing a biased principal component transformation upon said vector optimizing the across class variance while maintaining a constant within class variance of said components, selecting a number of said components, less than the number of said parameters, as said acoustic parameters, and processing said selected components for generating a speech recognition decision identifying the speech units in said speech input signal.