PVANA PVSYN

PVANA / PVSYN - phase vocoder I/O modules

Phase vocoder analysis.

Usage:

PVANA SIGIN L D I LFFT FMT TYPE WIN WTYPE

Inputs:

SIGIN

The input signal (the name of mono wave item).

L

The frame length in samples.

D

The decimation length in samples.

I

The interpolation length in samples

LFFT

The FFT length.

FMT

The spectrum format. The following values are supported:

0 - complex 1 - amplitude 2 - power Note that negative amplitudes are allowed for amplitude spectrum values (FMT==1).

TYPE

The algorithm type - 1..amplitude thresholding.

WIN

The window name: rectangle|hanning|hamming|blackman|kaiser|bartlett|taprectangle|nuttall|flattop|gaussian

WTYPE

The window type:

normal|dual|tight

Outputs:

A

The first part of the spectrum (depending on format FMT).

B

The second part of the spectrum (depending on the format FMT).

SR

The sampling rate.

Phase vocoder synthesis.

Usage:

PVSYN SIGOUT L D I LFFT FMT A B WIN WTYPE

Inputs:

SIGOUT

The name of the shell wave item for signal output (compatible with SIGIN).

See the above atom PVANA for a description of the other input parameters.

Outputs:

N

The number of frames.

I

-1

Function:

This atom implements the phase vocoder as published in the book "Elements of Computer Music" (R. F. Moore. Elements of Computer Music. Prentice-Hall, Englewood Cli#s, NJ. USA, 1990). The spectrum format (FMT) has to be set to 1 or 2 (amplitude or power) for this atom to truly represent a phase vocoder, for only then is phase-unwrapping and differentiation done. If the spectrum format is set to 0 (complex), this atom implements a channel vocoder. It can be used as an analysis or re-synthesis module for signal time-warping and/or signal modification methods in the frequency domain.

The advantage of the phase vocoder over other analysis/re-synthesis methods is the time and phase synchronicity of the input and output signals. For time-warping, the factor between the input and output timescales is defined by the ratio of the decimation to the interpolation length (D/I). If no timescale transformation should be performed, the values of D and I must be equal. In the current implementation, the "overlap-add" re-synthesis method is included, but not the "oscillator bank" method. This atom can therefore be used for time-warping, but not for frequency-warping.

Conditions for the parameters L, D and I:

L mod D = 0 and L mod I = 0 and L< LFFT

The example shows a filter circuit using PVANA/PVSYN for signal I/O. No timescale modification is performed (D=I):

Figure: Functional diagram of PVANA and PVSYN SPAtoms in the framework of the STx analysis-synthesis model.