11 Aug
2004
11 Aug
'04
11:22 a.m.
On Wed, Aug 11, 2004 at 01:56:52 +0200, Alfons Adriaensen wrote:
Step 2. above. With "fs/n" a mean of course a ripple with a period
of n bins. But don't waste your time with this, unless you are
curious :-)
I am curious, but more busy than curious sadly.
With 8x overlap probably even the effect of "fs/4" and "fs/8" would
be attenuated if there is windowing after step 3. IMHO, this windowing
is necessary: there is no reason why, in the general case, the result
of the IFFT would start of and go back to zero amplitude. I'd use
a square root raised cosine before the FFT and after the IFFT.
OK, thanks I'l try that. I would have thought that the IFFT would go
to zero at both ends though, as it was windowed at input.
Ok, in that case there should be no pre-echo at all,
as you
verified. But what then is that blob around the main impulse,
and the echo at 4.5 ms ? (not that it matters much, I don't
think any of them can be detected by ear).
The point of my example was to show that even a nearly flat,
'inaudable' frequency response can give audible artefacts in
the time domain when the filter is forced to be linear phase.
Oh, I see, yes, so dont :) I supect that the small ammount of noise
arround the impulse is a result of rounding errors in the FFT, but I dont
really have time to test it, and FFTs with greater recision are just too
expensive in CPU.
If the ripple is at "fs/2", it would be
removed anyway by any windowing
that is apllied before overlapping parts are added together.
Could you try a cosine ripple at "fs/4" or "fs/8" ?
Applied where? BTW, when do you apply windowing : before step 1,
after step 3,
or both ? What is the FFT size ?
Before 1, the FFT is 2048 bins, 8x overlap. The 8x overlap seems extreme. IF your bandpass
responses are not
'brick wall', and the EQ curves are also smooth, 8x overlap should
not be necessary.
The EQ curves are often not smoth, expecailly in the low frequency range,
as users make aparently smooth adjustments in the low octaves that only
span a couple of bins. It brings the lantecy down a bit too, which isn't a
huge issue, but doesn't hurt.
The crossover band joins are curretly quite sharp (2 bins I think), maybe
I should try smoothing them out more, but I didn't hear any sonic artifacs
when sliding them up and down with the compressors bypassed.
- Steve