Re: [iiwusynth-devel] Filter: Implemented, fixed

[Peter Hanappe]

On Thu, 2002-04-04 at 00:08, Josh Green wrote:
> On Tue, 2002-04-02 at 03:17, Christian Nentwig wrote:
>>
> > http://prdownloads.sourceforge.net/millisampler/Filterimplementation_tar.bz2
> > .
> 
> Tried it. Sounds much better now. Seems to be a little more CPU
> intensive than the older one (haven't tested this thoroughly though),

It does use a bit more CPU. The filter is on all the time. In the
previous version I erronously turned the filter of at Q=0 instead of
turning it into a non resonant filter. 

> but does sound more true to sound font standard. It would be nice to
> compare an SB Live! or something in windows to the sound of iiwusynth (I
> don't quite trust the Linux wavetable drivers). I did notice that very
> fast increases in filter cutoff (say in the modulation envelope release
> stage, with a sufficiently long volume release) causes a bit of filter
> instability (loud scratching sounds or noisy stuff) even when sample
> volume has completely died out, maybe thats whats supposed to happen?
> Probably not.

There was an error in the conversion of the center ferquency (my fault).
It's fixed in the CVS version. The filter still causes some clicks
sometimes but much less.

> > 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')
> > 
> 
> Cool, it was made with Smurf :)
> 
> > 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?
> > 
> 
> I haven't looked at the clock cycles consumed by FPU instructions for a
> while, but I do remember sin/cos being fairly costly. I'm not very
> familiar with iiwusynth's synthesis code, but it seems like it would be
> cool to make it somewhat pluggable. So you could choose different
> algorithms for the various effects for speed/quality trade offs. 

Anyway, I started profiling things a bit already. It'll be a fun job to
find the bottlenecks and try to optimize them.

> It
> would be real neat to have a non-realtime file rendering mode for
> iiwusynth. Then, once you get your MIDI files to your liking, use all
> the best effect modules and just render to a file :)

Should not be too hard to implement.

> Anyways, dreaming away. All this sounds good of course, but implementing
> it is another thing. I'm currently too busy with Swami to lend much
> support to iiwusynth, so..

I'll try to check out swami today.


I'm making progress with the chorus effect. I ripped it out of sox. I'm
tested it yesterday but it doesn't sound that good. Do any of you
actually use the chorus effect? I never liked it myself. 



> > Regards
> > 
> > Markus
> > 
> > PS: Nice sound font. My current favourite: El-Cheapo Organ :-)
> > 
> 
> Yeah its a nice sound font. I like how its all based on really simple
> waveforms, showing that soundfonts can be used for analog type stuff.

This brings me to another question. It would be nice if iiwusynth was
shipped with a default soundfont so that users always hear something
even if they didn't download a soundfont yet. It would be best to have a
GM soundfont so you can play the standard midi files you find on the
web. In that case iiwusynth could become a XMMS plugin. However, all the
GM soundfonts I tested were in general both huge in size and bad in
quality. Do you know of any that are acceptable and freely
distributable? We could use the patches that come with timidity.


Cheers!

Peter

> Cheers!
>       Josh Green
> 
> 
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