MATLAB: Scales at continuous WT and wcoher

cwtscal2freqscaleswcoher

Hello, I still cant quite understand what scales should I choose to examine my signal. Lets say sampling frequency of my signal is 2048Hz and I want to analyze frequencies "pseudofrequencies" rom 1Hz to 60Hz. What scales should I use? According to scal2freq function it would be 16:1048 a but according to Matlab tutorial it is:

dt = 1/2048;
NumVoices = 32;
a0 = 2^(1/NumVoices);
wavCenterFreq = 5/(2*pi);
minfreq = 20;
maxfreq = 500;
minscale = wavCenterFreq/(maxfreq*dt);
maxscale = wavCenterFreq/(minfreq*dt);
minscale = floor(NumVoices*log2(minscale));
maxscale = ceil(NumVoices*log2(maxscale));
scales = a0.^(minscale:maxscale).*dt;

And that gives completly different results. Thank you for help!

Best Answer

Its the same. Error was in that in the second case scales must be devided by dt.

Related Solutions

MATLAB: Proper wavelet scaling / restricted frequency analysis

Yes, it is possible, but you have to remember that the CWT is not as localized in frequency as the Fourier basis, so you have to give yourself some wiggle room. A sine wave will not be localized at one scale in the CWT. The way to do it best depends on whether you are using cwt.m or cwtft.m.

I'll create a signal consisting of 100-Hz and 300-Hz sine waves in noise. The 100-Hz signal will occur over the first 500 msec, the 300-Hz sine wave over the interval from 500 msec to 1 second.

Here is cwt.m:

 fs = 2e4;
 t = 0:1/fs:2-1/fs;
 x = ...
 2*cos(2*pi*100*t).*(t<0.500)+3*cos(2*pi*300*t).*(t>0.500 & t <1)+randn(size(t));
 dt = 1/fs;
 minscale = centfrq('morl')/(300*dt);
 maxscale = centfrq('morl')/(100*dt);
 scales = minscale-10:maxscale+10;
 cfs = cwt(x,scales,'morl','plot');

Now for cwtft (using an analytic Morlet wavelet)

MorletFourierFactor = 4*pi/(6+sqrt(2+6^2));
s0 = (0.002*MorletFourierFactor);
smax = (1/100*MorletFourierFactor);
ds =0.2;
nb = ceil(log2(smax/s0)/ds+1);
scales = struct('s0',s0,'ds',0.5,'nb',nb,'type','pow','pow',2);
cwtS1 = cwtft({x,dt},'scales',scales,'wavelet','morl');
sc = cwtS1.scales;
freq = 1./(sc*MorletFourierFactor);
contour(t,freq,abs(cwtS1.cfs));
xlabel('Time'); ylabel('Pseudo-Frequency');

MATLAB: Wavelet display problem – marked difference in frequency content between ‘contour’ and ‘imagec’

Unfortunately I don't have a lot of time at the moment to look into this, but how about just using surf()

WaveT='morl';
fs = 2e4;
t = 0:1/fs:2-1/fs;
x =  2*cos(2*pi*100*t).*(t<0.500)+3*cos(2*pi*300*t).*...
     (t>0.500 & t <1)+randn(size(t));
dt = 1/fs;
figure 
subplot(3,1,1)
title('signal')
plot(t,x);
subplot(3,1,2)
fc = centfrq(WaveT);
dt=1/fs;
minscale = centfrq(WaveT)/(300*dt);
maxscale = centfrq(WaveT)/(100*dt);
scales = minscale-10:maxscale+10;
Coeffs = cwt(x,scales,WaveT);
F = scal2frq(scales,WaveT,1/fs);
contour(t,F,abs(Coeffs)); 
xlabel('Time'); ylabel('Frequency');
axis xy
title('contour')
subplot(3,1,3)
surf(t,F,abs(Coeffs),'EdgeColor','none'); view(0,90);
axis tight;

Or simply just view this and you'll see the axes are correct

surf(t,F,abs(Coeffs),'EdgeColor','none'); view(0,90);
axis tight; xlabel('Seconds'); ylabel('Pseudo-Frequency (Hz)');

Best Answer

Related Solutions

MATLAB: Proper wavelet scaling / restricted frequency analysis

MATLAB: Wavelet display problem – marked difference in frequency content between ‘contour’ and ‘imagec’

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