11 Aug
2004
11 Aug
'04
9:19 a.m.
On Wed, Aug 11, 2004 at 12:24:36 +0200, Alfons Adriaensen wrote:
On Wed, Aug 11, 2004 at 09:32:11AM +0100, Steve Harris
wrote:
Its a full JAMin running with a flat freq response. I was testing it to see
how bad the pre-echo was.
I just checked jamin, and there is some ripple
around the impulse (as you
would expect), but it peaks at around -56dB, and I couldn't find traces of
a pre echo visibly, or audibly when amplified. There is what looks like
post echo though (at around -66dB, 4.5ms after), which is odd, I would
have expected the response to be symmetrical?
Yes, that's odd.
The wave which makes up the ripple looks like a
fs/2 sinewave.
It's not clear to me what exactly you did to obtain these results. I assume it's of the form
1. input --> FFT --> complex x(f)
2. y(f) = x(f) * r(f), with r(f) a real symmterical function
3. y(f) --> IFFT ---> real output
Note that for symmetry, r(f) must be of the form
1 + a * cos (b * f), not 1 + a * sin (b * f)
In this example r(f) = 1, its just a flat response.
Using a sine 'ripple' would only show up in
the imaginary component
the output, which is probably not even computed.
Yes, its a half-complex FFT.
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.
- Steve