[PD] latency issue

[Roman Haefeli]

On Mon, 2009-10-19 at 19:30 +0200, Bjørn Nielsen wrote:

> So Babsycos original question still goes unanswered (besides the
> really good advice about jack): can you decrease the latency with
> improving you hardware?

considering, that i am running pd 0.42 on jackd on ubuntu on a t61 with
a rme rpm soundcard attached and i can run pd with 7ms (real) latency -
i measured the roundtrip - this question can be answered with yes. the
bad thing is, that i cannot tell anything about why this is. i can only
assume, that probably rme soundcards perform well, linux performs well,
jack performs well (?).  

this latency i can get when setting the jackd buffer to 2x64 samples,
which introduces 2.9ms (@44100Hz) only for jackd. the rest seems to go
on the account of pd, which makes me think, that with current
implementation of pd, it's unlikely to reach values lower than 4ms
(again, i mean 'roundtrip' here, not the displayed value in whatsoever
software), no matter what hardware you use. 

even if it is possible to run pd at this low latency, i almost never do
it. this is mainly because you need to be so damn careful in order to
avoid drop outs. every little action, that might block pd only for a few
ms causes a drop out. and there are so many "don't"s when caring about
drop outs: no dynamic patching, no networking, no redrawing of arrays
(no moving of arrays), avoid too much logic in 0 logical time (or
distribute it over time), avoid any peaks in cpu load, etc. but yeah, if
you have a straight-forward fx patch and you don't touch it too much, pd
runs well also at low latencies.

coming back to the original question of babsycos: i'd really try another
OS. this has the advantage of trying a quite different setup without
having to spend more money on more hardware. if the mentioned soundcard
is supported by linux, i'd burn a copy of the pure:dyne live distro. it
has pd already installed and you don't need to alter the existing
installation - just boot from cd - and it is free (as in beer and as in
freedom). last time i tried it (which is quite a while ago) i was
impressed how well everything works.  

roman

 




	

	
		
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