Subject: Re: [linux-audio-dev] more about iiwusynth
From: Juan Linietsky (coding_AT_reduz.com.ar)
Date: Thu Jun 06 2002 - 07:14:26 EEST
On 05 Jun 2002 20:11:55 -0600
Josh Green <jgreen_AT_users.sourceforge.net> wrote:
> On Wed, 2002-06-05 at 17:11, Juan Linietsky wrote:
> > On 05 Jun 2002 05:09:17 -0600
> > Josh Green <jgreen_AT_users.sourceforge.net> wrote:
> >
> > > To LAD list members:
> > > I'm aware that there is a new Linux Audio Announce list, but I
> > > thought that since this is an initial release announcement, all
> > > would be forgiven :)
> > >
> > > Swami 0.9.0pre1 has been released. Swami is the new name of the
> > > Smurf Sound Font Editor. Along with the name change comes an
> > > entire object oriented source code re-write based on GObject
> > > with supporting libraries. Some of the most notable new features
> > > include:"iiwusynth" software SoundFont synthesizer support,
> > > removing the requirement of specialized hardware for SoundFont
> > > synthesis and delivering real time effects and SoundFont 2.01
> > > modulators for controlling generators via MIDI controls and more
> > > multi-item operations.
> > >
> > > Swami website: http://swami.sourceforge.net
> > >
> > > Developers wanted :)
> > >
> >
> > hey Josh! congratulations on this release! I've been waiting for
> > it for a while now ;) The only thing i still dislike is iiwusynth
> > being so incredibly slow :( Well, I'm downloading it!
> >
>
> Yes. This is something that is starting to be discussed again on the
> iiwusynth list, and is also my only gripe about it. Its gotten
> better though, a lot of it has to do with figuring out when voices
> have become perceptibly silent so they can be turned off or
> re-assigned. I'm not really doing much work on iiwusynth directly,
> since I've been pretty busy with Swami but I do manage to keep up on
> their discussions though. I think the synth sounds so good though
> that it somewhat out weighs the CPU consumption :) I'm certain it
> will get speedier though (like I said, it already has).
>
Well, after my previous mail i've got the latest iiwusynth tarball,
compiled it, tried it and found out that it was as slow as allways..
so i went into the code and found the critical zone (dsp mixer)
I tried to fix it, but handt have much success since i dont know the
input/output ranges of the vars. I dont know if peter hanappe reads
lad, but here's the list of things that i think that need to be done
in order to gain way more speed.
1-Change iiwu_voice_run_dsp macro to an inlined function, because it's
just too anoying to code ;) And I dont think there's performance loss
since the critical zone is INSIDE the loop.
2 - Get rid of the iiwu_phase_t and replace it for a 64 bit integer
(long long) which represents a 32.32 fixed point value. This way you
can take advantage of using the ADC instruction in the cpu
Peter said in there that he took the code from mozilla, which i think
it's perfect from mozilla since probably by the time that such code
was written, many compilers didnt support 64 bit int vars. gcc is
smart enough. Also, the index/frac vars seemed to me to be pointed to
a global sample pool buffer. Something sucky about this is that you
cant use 32 bit fixed point vars for smaller samples (or most of them
id say ;).
3 - Convert the code for the volume ramp (amp/amp_incr) to fixed point
4 - Convert the filter code to fixed point, that code is just eating
badly the cpu
5 - Convert the buffers to integers and only convert them to float
when mixing them too freverb.
6- basically, the less floats, the faster the mixer.. floats are
slow, and will _never_ be faster than integers for addition,
substraction and multiplication.
6-About the design of the filter/reverb/interpolation model...
I understand that peter is seeking an accurate player, but accuracy
depend on certain things...
First, about using hermite curves for interpolation...
I personally think that this is pointless, because in multisampled
instruments, linear interpolation works the same and uses way less
CPU. Cubics in interpolation are known to smooth the sound a bit when
downsampling, which is good, except for the point that downsampling is
a bad idea when you work with multisamples. Also, when you create
multisamples you usually filter high freqs out of them so the mix
better at the end.. Thats why i think, cubic isnt that better than
linear...so it should be given as an option (besides linear) if you
want a bit more overall quality in exchange of CPU. Also, it's good if
you want to write your song using linear (To take advantage of the
cpu) and then switch to cubic for the final mix.
Second, about chourus and reverb... I notice that they are mono
buffers... but still your reverb implementation (i didnt check it well
but looks like freevrb) supports reverb width.. this is a bit odd to
have if the reverb buffer is mono. Also with a chorus buffer you cant
do stereo chorus either (where you can specify an opposite direction
for chorus to be mixed at, i did this in cheesetracker and sounds
really nice)
Also, i noticed that pitch events dont work in iiwusynth?
well, that's all for now!
cheers
Juan Linietsky
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