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[fluid-dev] Re: Tuning issues with FluidSynth and JACK @ 48kHz

From: Josh Green
Subject: [fluid-dev] Re: Tuning issues with FluidSynth and JACK @ 48kHz
Date: Sat, 18 Feb 2006 15:34:01 -0800

I'm CC'ing the FluidSynth list on this discussion, I hope you don't
mind.  Its pretty important issue that needs to be resolved.  Feel free
to also CC the list and ignore any emails about non-subscriber approval,
I'll approve the messages ;)

On Sat, 2006-02-18 at 22:27 +0100, Christoph Eckert wrote:
> Hi Josh,
> thanks for the reply.
> > I believe this is actually a problem with the JACK driver code in
> > FluidSynth.
> OK, it already is a step forward to know that it can be a fluidsynth 
> related problem.
> > I remember another user reporting this, but I have not 
> > yet gotten around to checking it out.  Seems like a rather major
> > issue though.  Will look into it today.

I now recall that this issue was reported on Swami, so I didn't make the
connection that this was an issue with FluidSynth in general.

> Cool. If there are any findings I'd be happy to know about it.
> > Again, thanks for reporting this.
> No prob. As I cannot code I always try to write manuals, GUI 
> translations or even bugreports/feature requests as a contribution to 
> various projects.

It seems that FluidSynth is unable to change the internal sample rate
after its initially created.  In the ALSA driver code I found that a
warning is printed if the sample rate being used does not match what is
actually obtained from ALSA, it looks like this:
The sample rate is set to %d, the synthesizer may be out of tune

There is no such warning in the JACK driver and there is a comment like
  /* FIXME: change the sample rate of the synthesizer! */

In the JACK sample rate callback routine.  So in short, currently the
FluidSynth instance must be initially created with the correct sampling
rate.  When using the command line FluidSynth shell, this can be
accomplished like so:
fluidsynth -a jack -o synth.sample-rate=48000

Ultimately, FluidSynth should be modified to allow for dynamic changing
of the sample rate.  I'm not sure what this entails, since I don't have
a very complete overview of the FluidSynth code base yet.  For now, I
think it would at least be a good idea to put a warning in the JACK
driver if the sampling rate does not match.

> Best regards
> ce

        Josh Green

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