[PD] Re: [PD-ot] how low (latency) can you go?

Tim Blechmann tim at klingt.org
Sat Dec 16 16:52:43 CET 2006


On Sat, 2006-12-16 at 16:21 +0100, Patco wrote:
> IOhannes m zmoelnig a écrit :
> > Hans-Christoph Steiner wrote:
> >   
> >> Apple puts good audio hardware in their laptops.  I can get 14ms of
> >> latency on Mac OS X with Pd without really trying (I just set it to
> >> 14ms).  I can get down to 11ms if I don't mind clicks when I
> operate the
> >> menus and switch to other applications.
> >>     
> >
> > as always when it comes to latency and people tell numbers, i have
> to
> > ask my question: have you measured this? how? or was it just
> "putting a
> > number somewhere and assuming that it's the real latency"?
> > how much load do your settings allow?

from my experience, pd's audio backend is the bigger latency problem
than the audio hardware, especially on osx/windows, where vanilla pd is
using portaudio with pablio, which is unable to get below around 25 ms
of round-trip latency (i guess, hans was referring to one-way latencies)

> hello, the lowest latency i could get is with the CCRMA low latency 
> kernel patch.
> On a cheap internal audio card and an USB midi sport 2*2,
> connecting midi in to midi out gives me a latency measure on [timer] 
> between 15 and 25 ms with the lowest affordable buffers (about 5ms)
> as 

on linux, it's a bit better, but even with wini's alsa implementation,
the least round-trip latency it can produce without audio dropouts is
around 10ms. using it with smaller buffersizes there are severe timing
problems. 

with the callback-driven scheduler and the portaudio implementation from
devel, it's possible to get below 5 ms on all supported platforms,
though.

as for linux, it probably doesn't make any sense to use the rt kernel
patches with vanilla pd, as it's internal bottlenecks are a bigger
problem than the kernel.
and of course, these numbers are without _any_ gui interaction.

hth, tim

--
tim at klingt.org    ICQ: 96771783
http://www.mokabar.tk

I must say I find television very educational. The minute somebody
turns it on, I go to the library and read a good book.
  Groucho Marx
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