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

[Jan Newmarch]

Hi

Some things are getting clearer...

First off: it's only parts of nightsin.kar that distort badly - about 20
seconds worth, in different places. The rest plays fine. The bad bits
are when CPU usage hits impossible values - "top" says 99.9% and
"pidstat" says anything upto 380%! 

It isn't a universal issue:
        Files with no problems:
                Salsa.mid
                blowini.kar
        Files with problems:
                andwheni.kar
                awhiters2.kar - good test, errors occur early
                moneymon.kar
                ifeeltheearthmove.kar       
(Sorry, I don't know which ones are open content and which ones I
bought.)

Tools that give average values over the whole song, such as "prof",
aren't helping as much as they could, because the bad behaviour is
limited to small parts. For example, the interpolation takes a lot of
CPU, but changing that to linear (interp 1) or no interpolation (interp
0) made no difference to the bad bits.

The soundfonts used do not seem to affect things: memory usage is not
the issue, and there is no observable difference in sound quality
between General Sound (20% mem) and FluidR3 (40% mem).

QSynth is unusable out of the box on the RPi. It would be nice to use
it, but the sound is awful and CPU usage is up around 50% even when it
isn't playing anything! I'm testing with ALSA which is the layer below
Jack so that shouldn't be the difference.

I tried compiling with "cmake .. -Denable-floats" and without floats. No
observable difference in sound quality, so I would say that float vs
double is not the problem.

Okay, so what worked? First, you need the Raspbian image with FPU
support ("cat /proc/cpuinfo" shows "vfp"). Then set either of these
options:

1) polyphony=64 and reverb=false; or
2) rate=22050

Both of these options play all of my "bad" files okay. No need for
turning chorus off. But the peak CPU usage at the bad bits is still
hitting 80-99%, while the average usage is about 45%.  With the "good"
files, CPU usage stays in the range 20-60%. So I still don't know what
is the cause of the high CPU, but maybe this will help.

Cheers

Jan
-- 
Dr Jan Newmarch
Head of ICT and Commerce (Higher Education)

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