I don't think there's any issue - I just posted about the TrackSpacer plugin and the thread started up again. Actually what I've been trying to get across is that the Gibbs "nastiness' is ever present in both hardware and software implementations. It's just there in the underlying physics of sampling theory, even in the analog domain it seems :)
On Wed, Jun 24, 2020, 4:46 PM robert bristow-johnson < r...@audioimagination.com> wrote: > > is this the same thing we were discussing in March? wasn't that three > months ago? > > what, exactly, is the issue? > > there *are* some things in common between OLA phase vocoder and OLA fast > convolution. in fact, if you're willing to make your fast convolution less > fast than optimal, you can use a Hann or some other complementary window > but you *still* have to zero-pad it to prevent circular aliasing in the > time domain. the length of the FFT, N, must still be at least as large as > the non-zero length of the window, L, plus the length of the impulse > response, M, minus 1. > > N ≥ L + M - 1 > > the number of zero samples padded must be at least M-1 samples. > > the difference is, if a rectangular window is used for overlap-add fast > convolution, the processing frame advances by L samples every frame. but > if a Hann window is used (or another complementary window which requires > 50% overlap), then the frame advances only by L/2 samples, even though the > burden of computation involved in the frame is the same. but things will > look nicer in the frequency domain with the Hann window than they will with > the rectangular window (this Gibbs stuff). but the effect of any nastiness > is canceled if you're doing FIR fast convolution. but if you're doing > non-LTI stuff in the phase vocoder, then that friendly frequency-domain > behavior is more salient. > > -- > > r b-j r...@audioimagination.com > > "Imagination is more important than knowledge." > > > > On June 24, 2020 3:49 PM Zhiguang Zhang <ericzh...@gmail.com> wrote: > > > > > > Hi Russ, > > > > > > Yes. In the previous reference, there is no example for overlap-add. A > sine/cosine framework is a relatively simple one for OLA and fulfills the > necessary requirements. In the case of audio coding, various filterbanks > with different types of windows have been designed for 'perfect > reconstruction', and even window switching. Please refer to Bosi for a more > thorough treatment. > > > > > > Best, > > Eric Z > > > > > > On Wed, Jun 24, 2020, 3:44 PM Russell Wedelich <wedel...@gmail.com> > wrote: > > > Respectively Eric, I think you may be confusing two different use > cases for windows. Your recent reference is referring to constructing FIR > filters via the Windowing method of ideal brickwall filters. This is > different from a frequency domain convolution implementation of an FIR > filter (which may or may not explicitly apply a smooth window) which as far > as I can tell is the origin of this part of the discussion. > > > > > > -Russ > > > > _______________________________________________ > dupswapdrop: music-dsp mailing list > music-dsp@music.columbia.edu > https://lists.columbia.edu/mailman/listinfo/music-dsp
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