How can I find a threshold of amplitude and (in the same time) of frequency inside a spectrogram?
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I am analyzing 2 vectors of acceleration, ax, az in the frequency domain. They are vectors with sample frequency of 5 ms and gone through a pass band filter of 40 Hz.
My aim is to detect the spectrogram and identify the index of vector ax and/or az that has a certain threshold in amplitude and frequency both in the final spectrogram. I would like to put an alarm (identified with an asterisk) when I have a threshold of the power in a certain range of frequency.
Acc=[ax,az];
Fs=1/0.005;
N=length(az);
%p = nextpow2(N)
figure
nfft=80;
win=hamming(nfft);
nOvl=nfft*0.95;
[s,f,t,pxx] = spectrogram(az,win,nOvl,nfft,Fs,'psd');
waterfall(f,t,pxx')
xlabel('frequency(Hz)')
ylabel('time(sec)')
zlabel('PSD')
5 Comments
Mathieu NOE
on 20 Jan 2021
hello again
I wonder why we do it so complicated...
why not simply apply the band pass filter (10 - 30 hz) to your time data and look at the positive and negative spikes ?
this would be certainly sipmler and more accurate in time than going through the spectrogram stuff
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