Measuring the 'purity' of a sine wave using FFT (Matlab)

[SK1.618]

I have a range of sine waves I have obtained in an experiment.

I want to put a measure on the purity of these sine waves - how well the reproduce a theoretical sine wave.

Is there anyway I can analyse the FFT of the sine waves in Matlab and put a measure on the purity of the sine wave (e.g. by measuring the FWHM of the peak at the frequency of the sine wave)?

Thank you

 

[f95toli]

Yes, you could use the FFT function (see the examples in the documentation) or -if you have the right toolbox- estimate the PSD using e.g. Welch method (I recommend the latter if possible).

That said, if you have a range of sine-wave any lack of "purity" would not usually manifest itself as a wider fundamental peak in the spectrum; you are more likely to see other frequency components in the spectra; in particular harmonics which is why THD is such a popular measure of spectral purity.