Harmonic and frequency-locked loop pitch tracker and sound separ

Details Harmonic and frequency-locked loop pitch tracker and sound separ Harmonic and frequency-locked loop pitch tracker and sound separ

1995-01-09

1998-09-22

Knepper, David D.

395 218, G10L 904

Patent

active

058127372

ABSTRACT:
A quasi periodic signal is frequency warped by selectively frequency modulating it, thereby resulting in a signal that is stationary with a simplified spectrum which is more amenable to analysis. The resultant demodulated signal is low pass filtered resulting in an analytic signal whose phase winding rate is the frequency of the signal. The phase is differenced by multiplying the signal with a delayed version of itself creating an instantaneous autocorrelation. Thereafter the phase difference is measured with a complex arctangent to yield a resulting phase error. The resulting phase error is integrated by an integrator whose output value is the estimate of the frequency. This output frequency parameter is then used to update the demodulating signal thus closing the signal loop. In a second embodiment, a plurality of frequency locked loop trackers are servoed together centering each one of the trackers on a multiple of the fundamental frequency of the input signal. The resulting phase errors derived from the frequency lock loop trackers are weighted to improve system performance. The frequency corrections from each tracker are weighted with the inverse variance of its tracking performance. Accordingly, harmonics with low variance are weighted strongly, and harmonics in a noisy region of the spectrum and thus high variance will be weighted less strongly. The resulting fundamental frequency estimate is a minimum-variance, and is better than the best signal frequency locked loop estimate. The weighted phase error is then fed back to an integrator to yield a high resolution estimate of the target signal frequency. The amplitude envelopes for each partial signal can be easily extracted and used in conjunction with the fundamental estimate from each frequency lock loop tracker to resynthesize the signal in isolation from the mixture.

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