Importance

Loading Importance Indicators...

Abstract

The pitch frequency of voice signals in successive time frames at a voice coder may be determined as by (1) Cepstrum analysis (time between successive peak amplitudes in each time frame), (2) harmonic gap analysis (amplitude differences between peaks and troughs of the peak amplitude signals in the frequency spectrum) (3) harmonic matching, (4) filtering of the frequency signals in successive pairs of time frames and the performance of (1)-(3) on the filtered signals to provide pitch interpolation on the first frame in the pair and (5) pitch matching. The amplitude and phase of the pitch frequency and harmonic signals are determined by refined techniques to provide amplitude and phase signals with enhanced resolution. Such amplitudes are simplified digitally by (a) taking the logarithm of the frequency signals, (b) selecting the signal with the peak amplitude, (c) offsetting the amplitudes of the logarithmic signals relative to such peak amplitude, (d) companding the offset signals, (e) reducing the number of harmonics to a particular limit by eliminating selective harmonics, (f) taking a discrete cosine transform of the remaining signals and (g) digitizing the transformed signals. If the pitch frequency has a continuity within particular limits in successive time frames, the phase difference of the signals between successive time frames is provided. At a displaced voice decoder, the signal amplitudes are determined by performing, in order, the inverse of steps (g) through (a). These signals and the signals representing pitch frequency and phase are processed to recover the voice signals.

Loading the Abstract Image...

First Claim