[iiwusynth-devel] Filter: Implemented, fixed

[Christian Nentwig]

Hello,

found it. I hadn't tested sounds, which change the filter frequency over
time: recalculating the filter coefficients produced some
'zipper'-noise. But please let me know, if it still misbehaves.

The updated version is again at
http://prdownloads.sourceforge.net/millisampler/Filterimplementation_tar.bz2
.
There is also a sound font test file, which sweeps the filter to the
limit.
Patch 00: Slow filter sweep
Patch 01: Fast filter sweep
Patch 02: Very fast filter sweep ('typewriter-sound')

Speaking of it, there is something odd about the fcenter-information
that is produced by iiwusynth: A linear sweep (cents per second) should
reduce the frequency on a logarithmic scale. But the frequency change
seems to be linear (it reaches 0, that's impossible when sweeping on a
logarithmic scale).

Currently the filter coefficient calculation happens every IIWU_BUFSIZE
(64) samples once for each voice, and it includes a sin(x) and cos(x).
Has anybody an opinion on how CPU-intensive those are? Does it make
sense in the days of FPUs everywhere to use lookup tables?

Regards

Markus

PS: Nice sound font. My current favourite: El-Cheapo Organ :-)




Josh Green schrieb:
> 
> On Mon, 2002-04-01 at 10:44, Markus Nentwig wrote:
> > Hello again,
> >
> > now the filter is implemented. I have put a tar file with the
> > implementation on sourceforge for discussion (+backup...):
> > http://prdownloads.sourceforge.net/millisampler/Filterimplementation_tar.bz2
> > Have a look at it, I'm happy about any any comments.
> > I have tested it using a high-Q 440 Hz setting and the key A3, it works
> > just fine (and it's rather obvious that pianos sound darker with the
> > filter).
> >
> > I can merge the code into an up-to-date file version some day.
> >
> > Regards
> >
> > Markus
> >
> > PS:I'll be offline for a day or two.
> >
> 
> I gave it a try, but didn't really like the result :( Seems like the
> filter effect that is currently in iiwusynth sounds closer to what would
> be heard on SB hardware, but I haven't compared them directly. It did
> cause a bunch of cool radio tuning feedback sounds when upping the Q
> though :) There is just not right with the parameters perhaps? I tested
> some instruments in the Vintage Dreams sound font (what I do a lot of
> testing with). Some of them don't sound right at all. Seems like you
> have a pretty good grasp on the math behind it though, so I'm sure its
> just something wrong with your parameters or ?? Its nice to see that
> there is some work being done with the filter though. I like the sound
> and all, but it seems a bit unstable (have you figured out anything with
> this Peter?) Cheers!
>         Josh Green
> 
> BTW I just checked in some new changes to libsoundfont and Swami. The
> sample viewer is now working again and I changed libsoundfont's sample
> management to keep track of multiple storage methods for the same sample
> data (a sound font file and RAM for instance).
> 
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