Patent US 4,829,574

The disclosed system for extracting desired information from a speech signal includes means for taking overlapping samples of an utterance, computer means programmed to test each sample to determine whether it is voiced or unvoiced and for performing the following operations on each voiced sample: applying a 30 ms. Hamming window to smooth the edge of the signal and to ensure that false artifacts will not be present in the following processing stage, obtaining a magnitude spectrum using at least 1024 points Fast Fourier transform, obtaining the log of the magnitude spectrum, compressing the spectrum, performing a three-point filter algorithm a suitable number of times, expanding the spectrum so obtained and locating the dominant peaks in the resulting spectrum to give the information content contained in said speech signal. The specification also discloses the time equivalent of the above method. The transformed spectrum is smoothed to suppress low amplitude peaks at harmonics of the pitch frequency.