[PlanetCCRMA] little tome about the emi2|6

[Ryan Gallagher]

Mark,

As I understand things, the -p option is essentially
the buffer size (commonly found in asio control
panels, pt, dp, et al.).  For USB interfaces anyway
there is a strange relationship between sample rate
and buffer size.  The emagic and jackd default to a
sample rate of 48000 (good news).

Jackd documentation says;

"Due to the binary number system you should increase
the frames in multiples of 2 starting at 64.

For example: 64, 128, 256, 512, 1024, 2048, 4096,
8192"


BUT for some reason know only to Takashi (I know him
from email archives only), with USB interfaces like
the emagic and the quattro, sometimes buffer settings
that are (kinda) multiples of divisors of the sample
rate work better.  ie.

48, 96, 192, 384, 768,1536...

It's a bit of a mystery and it don't always seem right
but my experience proves it so.

Using a multiple of 64, the smalles buffer setting I
could make use of for PLAYBACK in ardour was 2048!

Using a multiple of 48 I can set buffersize to 480
with no (or few) xruns for playback.

(caveat: it seems some other jackd'ed applications
don't like the X/48 setting, ie freqtweak... but I
haven't researched it fully yet)

-ryan

--- Mark Knecht <markknecht@attbi.com> wrote:
> Ryan,
>    Did Takashi explain the use of '-p 480'? I've
> very curious about
> that.
> 
>    How does one make an informed choice? Maybe it's
> becasue I do not
> understand the 'emi's 48' comment? 
> 
> Clueless,
> Mark
> 
> 
> On Sat, 2002-12-28 at 17:51, Ryan Gallagher wrote:
> > Dear diary,
> > 
> > You know the setup;
> > 
> > pIII600 (overclocked a bit to 660)
> > ASUS P3B-F mobo 384mb
> > emagic emi 2|6 usb audio interface
> > RedHat 8.0 and CCRMA packages
> > 
> > Ardour jackd and I weren't getting along at all. 
> > Latency out of control, jackd -R -d alsa -d hw -p
> 2048
> > kinda helped but I still got xruns.
> > 
> > Thanks to  Mark Knecht, I changed the
> pci/usb/emagic
> > irq from 5 to 9.  Thanks to Takashi Iwai, I'm
> using a
> > multiple of the emi's 48 for the jackd
> > frames-per-period setting.
> > 
> > jackstart -R -d alsa -d hw -p 480
> > 
> > Now jackd, ardour and I are making great music
> > together.  I hope others can learn from my
> experience.
> > 
> > Next challenge; getting all 6 outs to work and
> > stopping xruns in xmms etc.
> > 
> > later-
> > -ryan
> > 
> > =====
> > --r--

=====
--r--

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