Should I trust Matlab FFT?

Thread Starter

Veracohr

Joined Jan 3, 2011
694
I wanted to measure the distortion of my function generator, and I discovered my oscilloscope seems to distort the signal slightly (always second and third harmonics around -40dB even after filtering). So I recorded the function generator as audio and tried two different FFT options to measure the distortion.

The first is an audio spectrum analyzer plugin which gave about 0.3% THD. This sort of thing isn't really intended for distortion analysis, but I figured FFT is pretty straight forward and there's not a lot of room for variation right?

Then I put the same audio file in Matlab and ran the FFT there, which gave me 0.06% THD. Now I wonder which to trust.
 
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