Comb-like peaks in frequency spectrum I am currently working on a project which involves measuring the sound produced by the onset of a vapour bubble in boiling water. All the experiments went perfectly well and I'm now trying to obtain a frequency spectrum from the signal. 

The sound-pulses produced by the bubbles only last about 40 ms max, simply too short to obtain a decent frequency resolution. That is why I'm measuring a numerous amount of almost identical pulses over a period of 5 seconds. The signal is being sampled at a rate of 100 kHz, which results in 500.000 samples. The interval between the sound-pulses is 95 ms ish as can be seen in the figure of the signal below:



EDIT: Added an additional figure of the signal:


When I create the frequency spectrum of the entire signal, I get this comb-like frequency spectrum with an interval of about 10 Hz between the peaks (which corresponds to the 95 ms time interval, but I would then rather expect a peak at 10 Hz in the spectrum):



I can't really get much information from this spectrum. I do know for instance that there should be a peak at around 167 Hz by looking at the time-domain (there's a small sine wave visible with about 6 ms peak to peak). The envelope of the spectrum does resemble the spectrum of a single sound pulse as shown below (but way less accurate):



The matlab code I used for the fourier transform was:

y_fft = abs(fft(y-mean(y)));
y_fft = y_fft(1:Nsamps/2);
f = Fs*(0:Nsamps/2-1)/Nsamps;    %Prepare freq data for plot

Does anyknow how to get a usefull spectrum in this situation or please tell me what I'm doing wrong?

Thanks in advance,

Marc
Your signals look quite similar to vowel signals - in which a periodic pulse train is filtered by a resonant filter.

I suggest you to look into AR modelling to decompose your signal into a residual, and a set of AR coefficients. The spectrum of the residual will give you the "pulse train" component of your signal (a sharp peak every time a bubble is produced) ; while the frequency response of the all-pole filter associated with the set of AR coefficients will contain information about the sound of each bubble. The 167 Hz peak you are looking will be easy to spot on the later.