3 May
2012
3 May
'12
10:21 a.m.
On 05/03/2012 04:26 AM, Joel Roth wrote:
On Tue, Apr 17, 2012 at 05:09:52PM +0000, Fons
Adriaensen wrote:
Capture latency in above message is a wrong. It was reported a while
back: check jack-devel archive Dec 2010:
http://old.nabble.com/jack-%281-and-2%29-latency-reporting-td30420262.html
On Mon, Apr 16, 2012 at 05:21:47PM -0400, S.
Massy wrote:
Thanks for clarifying this.
I understand that the round trip delay for the soundcard is the sum
of capture port latency and playback port latency, plus whatever
additional delay is associated with the AD/DA converters.
However I see what appears to be a discrepency for
the latencies reported by jackd (2 + 2 periods roundtrip)
and by jack_lsp -l (1 + 2 periods round trip).
This is for jackd2.
jackd says:
configuring for 44100Hz, period = 1024 frames (23.2 ms), buffer = 2 periods
ALSA: final selected sample format for capture: 32bit integer little-endian
ALSA: use 2 periods for capture
ALSA: final selected sample format for playback: 32bit integer little-endian
ALSA: use 2 periods for playback 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. However, jack_lsp -l says:
system:capture_1
port latency = 1024 frames
port playback latency = [ 0 0 ] frames
port capture latency = [ 1024 1024 ] frames
system:capture_2
port latency = 1024 frames
port playback latency = [ 0 0 ] frames
port capture latency = [ 1024 1024 ] frames
system:playback_1
port latency = 2048 frames
port playback latency = [ 2048 2048 ] frames
port capture latency = [ 0 0 ] frames
system:playback_2
port latency = 2048 frames
port playback latency = [ 2048 2048 ] frames
port capture latency = [ 0 0 ] frames
Is this inconistent, or is there some other explanation?
with jack2, there's also the difference of sync (jackd --sync .. -d alsa
...) vs. async mode. The latter adds 1 period of output latency.
see also:
http://wiki.linuxaudio.org/wiki/jack_latency_tests
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.
Great to have these details available for unschooled
developers as myself!
Regards,
Joel
> Ciao,
>
> --
> FA