[SciPy-User] Accurate Frequency Measurement

Seth Nickell snickell@gmail....
Tue Nov 30 00:05:47 CST 2010


Well. That takes the cake. I had looked up the performance difference
between power of 2 vs. not on fftw and figured I could accept 20%
slower, but in this case it made the difference between "fft takes 1s"
and "fft hasn't yet returned after 5 hrs". I can now do a long enough
fft to find the frequency within a hundredth of a hz, and have found
that adequate for my purposes.

Thanks Charles!

On Mon, Nov 29, 2010 at 10:10 PM, Charles R Harris
<charlesr.harris@gmail.com> wrote:
>
>
> On Mon, Nov 29, 2010 at 3:19 PM, Seth Nickell <snickell@gmail.com> wrote:
>>
>> I'm trying to measure the frequency of several sin 'tones' in a signal
>> to within a hundredth of a Hz. I've made a 200s recording of the
>> signal (44100 Hz wav file), but find that I cannot reasonably take an
>> fft of the entire signal (takes 'forever'). The size of fft that seems
>> to not take forever only gives me a resolution of a tenth of a Hz. The
>> sin tones have the highest amplitudes by a long shot (i.e. the signal
>> isn't very noisy). I've considered using a sin tone generator and
>> using my ears+destructive interference to find the tones, but I'd like
>> to be able to re-run this procedure on hundreds of signals, and I
>> wouldn't be confident in the precision I could achieve.
>>
>
> Out of curiousity, did you use a power of two for the length of the
> transform?
>
> Chuck
>
>
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