![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/184381/image.jpeg)
Code for signal analysis
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Thiago Petersen
on 13 Aug 2016
Commented: Thiago Petersen
on 14 Aug 2016
I trying to analyse some electric signal data but I'm still a Matlab beginner and need help. I use the code bellow just to plot time and signal, but i want to stract the repetition rate of the signal (Hz/number of pulses per second). I think this is possible if i delimite a threshold for the start. Other problem is: i have two signals together in the same file (one big, other little, a example in the figure). Its possible to calculate the repetition rate for each signal? Follow a example of my data.
Thanks for reading
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/155714/image.jpeg)
file = 'filename';
signal=wavread(file); % signal
fs = 48000; % sample rate
t=[1/fs:1/fs:length(signal)/fs];
plot(t,signal);
2 Comments
John BG
on 14 Aug 2016
Thiago
You are not supplying enough information.
the signal.mat is not a signal, but 2, without time reference, without the time reference you keep the readers doing guesswork, let me explain:
s=load('signal.mat');
y1=s.signal(:,1);y2=s.signal(:,2);Y=[y1 y2];
now listen to them
Fs=40000;signalObj_Y1=audioplayer(y1,Fs);play(signalObj_Y1)
Fs=55000;signalObj_Y1=audioplayer(y1,Fs);play(signalObj_Y1)
Fs=155000;signalObj_Y1=audioplayer(y1,Fs);play(signalObj_Y1)
As you can hear, attempting to find the Pulse Repetition Frequencies (PRF1 and PRF2) without timebase, is pointless.
Then one may consider that from the graph above:
10 pulses (the larger amplitude signal), 8 intervals, of 50ms, this makes PRF1 ~ 25Hz
14 pulses of the smaller amplitude signal, on same really short 8 intervals of 50ms each, this is, PRF2 ~ 35Hz
So, where are the 50Hz (Euroland) or 60Hz (US) ?
If you are analysing conducted signals along an electric line you should take a frequency scan well above the audio limits, because just with ADSL and car engine spark plugs, and the whole lot of mobile phone towers around, if not any wired Ethernet plugged to a nearby mains, you really have a lot of noise and interference that is not present in the above graph,
So could you please be so kind to supply the time base of the audio signal?
Question: why do you supply 2 signals in the signal.mat?
Observation:
Y_fft1=fft(y1);plot(abs(Y_fft1));
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/184381/image.jpeg)
the short graph with 50ms intervals looks like the signal with slower PRF, this is PRF1~25Hz is has stronger amplitude, yet out of the fft of the complete signal supplied in signal.mat it appears to be the other way around, doesn't it?
So the signal with 2 clear tones, or buch of tones, seems to have both wide variations of amplitude and frequency along the supplied sample, would it make sense to also ask for f1_min f1_max f2_min and f2_max?
Awaiting answer
Accepted Answer
Image Analyst
on 13 Aug 2016
I'd take the absolute value of the signal (to flip the bottom part up), then I'd threshold at 0.3 and 0.06 to get the two parts of the signal - the high spikes and the shorter spikes. Then use bwlabel to give an ID number to each spike and use regionprops to compute the centroid of each thresholded spike. Once you know that, you can get the average time between spikes, or whatever other information you might want. Untested code (because you didn't include your data) is below:
bigSpikes = abs(signal) > 0.3;
[labeledSpikes, numberOfSpikes] = bwlabel(bigSpikes);
props = regionprops(labeledSpikes, 'Centroid');
allCentroids = [props.Centroid];
xCentroids = allCentroids(1:2:end)
meanSpacingTall = diff(xCentroids)
Do the same for shortSpikes
shortSpikes = abs(signal) > 0.06;
[labeledSpikes, numberOfSpikes] = bwlabel(shortSpikes);
props = regionprops(labeledSpikes, 'Centroid');
allCentroids = [props.Centroid];
xCentroids = allCentroids(1:2:end)
meanSpacingShort = diff(xCentroids)
3 Comments
Image Analyst
on 14 Aug 2016
How about smoothing with a Savitzky-Golay filter to get rid of oscillations then filtering out spikes that are too narrow (are noise)?
![](https://www.mathworks.com/matlabcentral/images/broken_image.png)
s = load('signal.mat')
signal = abs(s.signal(1:4500));
smoothedSignal = sgolayfilt(signal, 2, 101);
plot(signal);
hold on
plot(smoothedSignal, 'r-', 'LineWidth', 2);
grid on;
% Get all spikes, tall and short.
allSpikes = smoothedSignal > 0.03;
% Get rid of spikes less than 50 elements wide.
allSpikes = bwareaopen(allSpikes, 50);
[labeledSpikes, numberOfSpikes] = bwlabel(allSpikes);
props = regionprops(labeledSpikes, smoothedSignal, 'Centroid', 'MaxIntensity');
allCentroids = [props.Centroid];
xCentroids = allCentroids(1:2:end)
% Get the max intensity in each spike.
maxIntensities = [props.MaxIntensity];
% Find tall spikes
tallSpikes = maxIntensities > 0.1;
% Find short spikes
shortSpikes = ~tallSpikes;
% Plot a B at the top of every big spike
for k = 1 : length(xCentroids)
thisX = xCentroids(k);
thisY = smoothedSignal(round(thisX))+0.02;
if tallSpikes(k)
% It'a a tall spike.
text(thisX, thisY, 'Tall', 'Color', 'r', 'FontSize', fontSize);
else
% It'a a short spike.
text(thisX, thisY, 'Short', 'Color', 'r', 'FontSize', fontSize);
end
end
meanSpacingTall = mean(diff(xCentroids(tallSpikes)))
meanSpacingShort = mean(diff(xCentroids(shortSpikes)))
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