Re: [fluid-dev] problems with fluidsynth 1.1.6 on a raspberry pi

[Aere Greenway]

Jan & David:

In my opinion, limiting the polyphony (I presume that is what you mean by "limiting the voices") does not adversely affect the sound.  

What is using up the CPU, is voices still being 'sounded' that have long before faded to where they are inaudible.  

If Fluidsynth works similarly to the EMU10K1/2 (Soundblaster & Audigy) chip, it should 'take-out' the oldest voices first, though I don't know if that is actually the case.  

I think the Soundblaster and Audigy soundcards have a polyphony limit of 64 (I have also heard that the limit is actually 48).  And since the pieces sounded fine on my Soundblaster card, I tried setting the polyphony to 64, and it also sounded perfectly good, and cut down the processor load significantly.  

Trying that worked fine, with no detectable degradation in sound.  

Since I use Qsynth, I change this by changing the "Polyphony" parameter of the "Audio" tab (visible after clicking the "Setup" button.  I do not know how to make the same change using command-line parameters.  


- Aere

-----Original Message-----
From: David Henningsson <address@hidden>
Reply-to: FluidSynth mailing list <address@hidden>
To: FluidSynth mailing list <address@hidden>
Subject: Re: [fluid-dev] problems with fluidsynth 1.1.6 on a raspberry pi
Date: Sun, 18 Nov 2012 12:51:58 +0100

On 11/18/2012 11:07 AM, Jan Newmarch wrote:
> Thanks to Christian and Aere. Here are some more results on a file
> nightsin.kar of various choices using pidstat:
>
> Version 	flags 	sound font 	cpu % 	memory % 	comments
> 1.1.5 	none 	FluidR3_GM 	75% 	43% 	unlistenable
> 1.1.5 	-z 4096 	FluidR3_GM 	70% 	43% 	unlistenable
> 1.1.5 	-z 4096 	GeneralUser 	76% 	20% 	unlistenable
> 1.1.6 	none 	FluidR3_GM 	80% 	40% 	still distorting
> 1.1.6 	-z 4096 	FluidR3_GM 	75% 	40% 	distorts when usage > 90%
> 1.1.6 	-z 4096 	GeneralUser 	65% 	none shown 	distorts when usage > 90%

Thanks for providing a good test case. I'm not familiar with pidstat - 
could you state the command line do you use for this, for an accurate 
comparison?

It looks like the CPU % maybe does not differ that much.

Actually, I recently got hold of a Nexus 7 running Ubuntu [1], which has 
a Tegra 3 core. When running NIGHTSIN.KAR (found at [2]), it does indeed 
use a lot of CPU. It runs fine for the most part, but occasionally 
breaks up. (This is with -z 4096.)

Running a quick perf analysis of it, the top CPU using functions are:

30% - fluid_rvoice_dsp_interpolate_4th_order
27% - fluid_rvoice_buffers_mix
13% - fluid_iir_filter_apply
  9% - fluid_revmodel_processmix

The interpolation can be reduced, but only inside the shell it seems 
like, so that would help some (at the expense of quality, as usual).

Reducing the number of voices would be the first thing to try IMO, that 
is usually not that hearable hopefully.

But this is indeed an interesting optimisation problem. At least 
fluid_rvoice_buffers_mix should be able to run faster I believe. I'll do 
some experiments with it when I have some more time.

// David

[1] https://wiki.ubuntu.com/Nexus7

[2] http://www.swissdom.cc/midis/karaoke-internacional-1/n/

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Sincerely,
AereSincerely,
Aere

Sincerely,
Aere