[time-nuts] Calculate spectral content from a series of zero crossing time stamps?

Magnus Danielson magnus at rubidium.dyndns.org
Thu Feb 10 18:53:09 UTC 2011


On 10/02/11 06:13, jimlux wrote:
> On 2/9/11 2:08 PM, Tijd Dingen wrote:
>>
>>
>>> The autocorrelation processing is O(N^2) while the DFT can be done in
>>> O(N log N) when using FFT. As usual these can be implemented in reversed
>>> order such that first the FFT is done to the phase jitter and
>>> auto-correlation
>>> can be found using O(N) post-processing.
>>
>> If it can be done in N log N that would be nice. :)
>
> autocorrelation:
> FFT of input sequence, multiply each bin by itself, inverse FFT
>
> So N(2logN+1) operations

Eh, no. In this case we wanted the frequency form, so no inverse FFT. 
You forgot to keep an eye on the big picture.

Cheers,
Magnus



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