#155 Spectrum view reports wrong Hz frequencies, if large frame

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nobody
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5
2010-08-03
2010-08-03
Dan Stowell
No

* Load an audio file (preferably one with some structured frequency content, e.g. with a strong tone at a known freq). In my case it was birdsong recordings, WAV, 44.1 kHz.
* Get a spectrum (not a spectrogram). Identify a notable feature of the spectrum at a short-ish resolution (in my case it was a dropoff due to a shelving filter at around 18 kHz, easily visible in an FFT of size 8192). I do this by moving my mouse over the feature, and looking at the visual readout of bin number and frequency.
* Change window size to 262144.
* Mouseover the feature again. The frequency is not reported correctly. For me the bin number was 111485--111616, which seemed about right, but the frequency was reported as 2370--2392 Hz (it should have been something around 18 kHz).
I can manually calculate what the real frequencies should have been reported as (assuming the bin indices are OK): 18754--18777 Hz. So about a factor of 8 wrong.

Discussion

  • Dan Stowell
    Dan Stowell
    2010-08-03

    Aha - it looks like the frequencies are correct as far as roughly 16384 (i.e. 2**14), after which point they wrap around.