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tfrcw

Choi-Williams time-frequency distribution

Calling Sequence

[TFR,T,F] = tfrcw(X
[TFR,T,F] = tfrcw(X, T)
[TFR,T,F] = tfrcw(X, T, N)
[TFR,T,F] = tfrcw(X, T, N, G)
[TFR,T,F] = tfrcw(X, T, N, G, H)
[TFR,T,F] = tfrcw(X, T, N, G, H, SIGMA)
[TFR,T,F] = tfrcw(X, T, N, G, H, SIGMA)
[TFR,T,F] = tfrcw(...,'plot')

Parameters

X :

A Nx elements vector (auto-CW) or a Nx by 2 array signal (cross-CW).

T:

a real Nt vector with elements in [1 Nx] : time instant(s) (default: 1:NX).

N:

a positive integer: the number of frequency bins (default:NX). For faster computation N should be a power of 2.

G:

a real vector with odd length: the time smoothing window, (default :Hamming(N/10)).

It will be normalized such as the middle point equals 1 to preserve signal energy.

H :

real vector with odd length: the frequency smoothing window,(default: Hamming(N/4)).

It will be normalized such as the middle point equals 1 to preserve signal energy.

SIGMA :

a positive scalar: the kernel width (default : 1).

TRACE :

A boolean (or a real scalar) if true (or nonzero),the progression of the algorithm is shown (default : %f).

'plot':

if one input parameter is 'plot', tfrqview is called and the time-frequency representation will be plotted.

TFR :

A real N by Nt array: the time-frequency representation.

F :

A N vector of normalized frequencies.

Description

tfrcw computes the Choi-Williams distribution of a discrete-time signal X, or the cross Choi-Williams representation between two signals.

Examples

Interactive use

N=128;
sig=fmlin(N,0.05,0.3)+fmlin(N,0.15,0.4);
g=window("kr",9,3*%pi); h=window("kr",27,3*%pi);
t=1:N; tfrcw(sig,t,N,g,h,3.6,1,'plot');

Non interactive use

N = 128;
sig = fmlin(N,0.05,0.3) + fmlin(N,0.15,0.4);
g = window("kr",9,3*%pi);
h = window("kr",27,3*%pi);
t = 1:N; 
[TFR,T,F] = tfrcw(sig,t,N,g,h,3.6);
clf; gcf().color_map = jetcolormap(128);
grayplot(T,F,TFR');

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