Re: [LAU] Estimating JACK latency - Linux-audio-user

3 May 2012

On 05/03/2012 10:43 AM, Joel Roth wrote:
...
  On Thu, May 03, 2012 at 10:21:16AM +0200, Robin Gareus
wrote:
  Capture latency in above message is a wrong. It
was reported a while
 back: check jack-devel archive Dec 2010:  
 Thanks

  with jack2, there's also the difference of
sync (jackd --sync .. -d alsa
 ...) vs. async mode. The latter adds 1 period of output latency.  
 I'll need to read about this. --sync is listed in --help,
 but not in the man page. 
http://www.grame.fr/~letz/jackdmp.html

...
  I hope the difference shows up in
get_jack_port_latency_range()! 
It does. The output latency is one period longer in async mode.

...
   see also:
   http://wiki.linuxaudio.org/wiki/jack_latency_tests   
 And again. This is very helpful.

This wiki-page is a bit outdated (it's from before the new latency API
was introduced) but item (2) under
http://wiki.linuxaudio.org/wiki/jack_latency_tests#interpretation_and_analy…
describes the same bug that you stumbled over.

(1) was actually solved: The additional latency for USB devices comes
from ALSA's USB driver implementation. Clemens explained the details in
the same thread on jack-devel "Re: Differences in latency between USB
and internal audio interfaces"  December 9, 2010.

ciao,
robin