Re: a question about phase vocoder

Hi,Jim and everyone!

Please pardon me. Maybe I didn't make myself understood.

If explainiing STFT as linear filtering, then its hop size

must be set according to the type of analysis window and

widow length so that the original signal can be restored from the time

downsampled STFT. It is exactly right!

My question is:

The outputs of phase vocoder are time-variable ampltitude

(or say, instantaneous amplitude) and instantaneous frequency.

In the discrete-time case, instantaneous frequency have to be

computed as difference of phase or as given by

(J. L. Flanagan and R. M. Golden, ¡°Phase vocoder,¡±).

In the first case, phase must be extended beyond

the principal value interval [-pi,pi]. If the hop size

is 1, this job is easy. If not, how to do then?

In the latter case, differential of STFT's real part and

imaginary part have to be estimated by discrete-time

filtering of them, for example, the first order for ward or backward

difference. If the hop size is not 1, differential can still be replaced

by difference? The real part and imaginary part of STFT are

band-limited in what extent? How to set a reasonable hop size?

Best

Regards!

Superk (Kun She)

intel_ghost@xxxxxxxx

2005-12-29