It's not exactly Cooley-Tukey. In Cooley-Tukey you take two _interleaved_ DFT's (that is, the DFT of the even-numbered samples and the DFT of the odd-numbered samples) and combine them into one longer DFT. But here you're talking about taking two _consecutive_ DFT's. I don't think there's any cheap way to combine these to exactly recover an individual bin of the longer DFT.
Of course it's possible you'll be able to come up with a clever frequency estimator using this information. I'm just saying it won't be exact in the way Cooley-Tukey is. -Ethan On Mon, Nov 5, 2018 at 12:28 AM, gm <g...@voxangelica.net> wrote: > > > Am 05.11.2018 um 01:56 schrieb gm: > >> so you do the "radix 2 algorithm" if you will on a subband, and now what? >> the bandlimits are what? the neighbouring upper and lower bands? >> >> how do I get a frequency estimate "in between" out of these two real >> values that describe the upper and lower limit of the band but have no >> further information? >> >> thank you. >> > The way I see it: > > If you do that 2 point transform on a band you get 2 data points instead > of one (or rather instead of two sucsessive ones of course), representing > the upper and lower bandwith limit of the band, but not very well seperated. > But if you take the result of the previous frame also into account you now > get 4 points representing the corner of a bin > of the original spectrum so to say, however in bewteen spectra, and you > now can do bilinear interpolation between these 4 points. > > But in the end this is just crude averaging between two sucessive spectra, > and I am not sure if it sounded better > or worse. It's hard to tell a difference, it works quite well on a sine > sweep though. > > But there must be a better way to make use of these 2 extra data points. > > In the end you now have the same amount of information as with a spectrum > of double size. > So you should be able to obtain the same quality from that. > That was my way of thinking, however flawed that is, I'd like to know. > > > > _______________________________________________ > dupswapdrop: music-dsp mailing list > firstname.lastname@example.org > https://lists.columbia.edu/mailman/listinfo/music-dsp > >
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