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

From: S. Christian Collins
Subject: Re: [fluid-dev] problems with fluidsynth 1.1.6 on a raspberry pi
Date: Fri, 23 Nov 2012 21:51:23 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0

Sorry to keep repeating this, but have you tried switching FluidSynth to
linear interpolation yet? It seems a lot of your CPU usage is tied up in
the 4-point interpolation that FluidSynth defaults to.

On 11/23/2012 07:27 PM, Jan Newmarch wrote:
> On Wed, 2012-11-21 at 16:26 +0100, David Henningsson wrote:
>> That is a very valid point; we might not strive to eliminate the average 
>> CPU as much as the worst-case CPU, even if both are important.
>> Maybe you could run "perf top -d 1" and monitor that, to see if anything 
>> special happens while the CPU maxes out?
> No luck :-(. The output looked the same for good and bad bits
>> I have another idea too; maybe we're trashing the L1 cache? If so, 
>> running with -z 1024 or -z 512 might give better result (combined with 
>> using floats instead of doubles). Here, -z 1024 gave better results, but 
>> not by much. The Raspberry Pi does not seem to have a L2 Cache (for CPU 
>> usage), so it might diff more for you.
> Just setting -z to either 512 or 1024 and floats instead of doubles
> didn't work by itself.
>> If we do an extremely rough calculation: We have a computer of 1 GHz, a 
>> sample rate of 50 kHz, and 100 voices; that gives us only 200 cycles per 
>> voice and sample. And we still have to do several floating point 
>> calculations every sample. So this leads me to believe that maybe there 
>> is no holy grail solution to this problem, nothing obvious we're missing 
>> that causes this CPU usage. Maybe it's more of trying one thing here and 
>> another thing there.
> Sorry to pull in the "competition" here... Timidity gives CPU usage of
> around 70-90% on nightsin.kar. But it doesn't have the blowouts to above
> 100%, and plays okay (just). I don't know what the default settings are
> for Timidity though. Maybe it is just fine tuning, although Aere is
> getting good results on a slower CPU.
> On another tangent, running Fluidsynth as a server to the ALSA MIDI
> sequencer alsa_seq plays okay with rate set to 22050.

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