[LAU] Estimating JACK latency

Fons Adriaensen fons at linuxaudio.org
Tue Apr 17 17:09:52 UTC 2012

On Mon, Apr 16, 2012 at 05:21:47PM -0400, S. Massy wrote:

> Okay, so for a standard 2 periods of 128 frames each, my nominal dddelay
> is 256 frames or 5.3ms at a sr of 48k, twice that for a round-trip.

No. The nominal roundtrip-delay (physical input to physical output
if you connect the corresponding ports directly) is period * nperiods.

1 * period occurs at the input, (nperiods - 1) * period at the output.

If you masure it using jack_delay you will in most cases find a value
that is a bit higher, this is due to delay in AD/DA converters etc. For
some types of soundcard (e.g. USB) the real latency can be significantly
higher than the nominal value. You can tell Jack about this using the 
-I and -O options.

The extra delay when making a loop such as Ardour -> jconvolver -> Ardour
is one period.



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