Selected bin oscilation in STFT I am looking for a noisy signal using STFT. My window length is 128 and I am using 75% overlap. I am using a Hanning window before running the FFT process. I am using Quinn's 2nd estimator for interpolation after the fact.
What I observe is the detected signal jumping frequently between bins. In the picture below the red is the detected frequency (around 190Hz) the green is the detected bin (sampling rate is 1000Hz so bin size is 7.8Hz)



What I would like to know is - is this likely to be an artifact of the method I am using, or is it simply that the frequency is varying a lot. What would be a suitable way of coming up with a more reliable prediction without losing time resolution?
I am using a low pass filter at 20Hz to smooth the output, but it still does not remove this oscillation.

Here is a full FFT of the signal over a much long time period:



I guess that indicates that its simply the signal causing this.
I switched to using the normalized power spectrum and changed my output filtering from two-pass to one-pass. This appears to have made a massive difference:



It's difficult to tell from the picture but the response is actually much smoother and you can see that the selected bin is not jumping around in the same way. The two pass filtering I was using in particular caused a lot of ringing after sudden impulses and a one-pass filter was generally much, much better.