Finding multiple x-intercepts for a dataset

I have a 2-D dataset that crosses the x-axis multiple times.

I would like help making a function that will return all the x values at which y = 0.

Any help for a day 1 newbie would be much appreciated!

Possibly helpful background: I'm analyzing sound spectra. I would like to find the peaks of the signal by finding where the 1st derivative crosses the x-axis.

Answer 1

[William Rose]

@Jacob Hohsfield,

Matlab has a very nice peak finding function, findpeaks(), help here: It has nice options, including threshold, minimum peak prominence, minimum horizontal (i.e. time or frequency, in your case) separation, etc.

[William Rose]

findpeaks() returns the peak amplitudes and the peak locations (i.e. frequencies, if analyzing a spectrum).

[Jacob Hohsfield]

I think this is what I need. Thank you!

[William Rose]

@Jacob Hohsfield, you;re welcome, and good luck on your work.

Answer 2

[William Rose]

@Jacob Hohsfield,

You said you have a 2D dataset. If you mean the spectrogram, the time dependent Fourier transform, then findpeaks() is not the right answer since it is for 1D signals.

See this quesiton and answer: https://www.mathworks.com/matlabcentral/answers/399125-how-can-i-find-the-peaks-of-a-surface-i-e-2-d-data-instead-of-1-d