[LAD] JACK + PA Latency

[Fons Adriaensen]

On Sat, Sep 28, 2013 at 12:42:26AM +1000, Patrick Shirkey wrote:

> 1: Why PA is reporting 10ms for the stream buffer but jack_delay is giving
> the results below.
> 
> 2: Why PA is reporting 10ms for the stream buffer when I am running jack
> at 64 frames/period and ecasound too.
 
> 3: Where the fluctuating measurements from jack_delay are coming from in
> the graph as PA Stream Buffer is static at 10ms and ecasound is basically
> in pass through with a 64/48k buffer same as JACK. A back of the envelop
> estimation suggests latency should be stable well under 20ms including the
> 10ms set aside for the PA Stream buffer.

(1) and (2) you should really ask to the PA author(s).

Regarding (3):

* The results you included can't be consecutive outputs of jack_iodelay
  at least not as I wrote it. So what is the real timing of them ?

* How is ecasound taling to PA ? Some native PA interface ? ALSA ?
  Any ALSA 'plugs' in the chain ?

* Going from 65216 to 64 is just an overflow modulo 2^16 (which the
  maximum that jack_(io)delay can measure. Apart from that, the
  delay seems to be continuously increasing, but since you edited
  the result it's not possible to say how fast.

Either PA is adding more and more buffering as time goes on, or
it is resampling and doing a very bad job at it.


Hint: use jack_delay (on my website), it will output less clutter
(one line per value), and is also more resistant to abnormal
circumstances.


Ciao,

-- 
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)