linuxaudio.org

On Tue, Apr 17, 2012 at 05:09:52PM +0000, Fons Adriaensen wrote:

quoted text
> 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.

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
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?
> If you masure it using jack_delay you will in most cases find a value

quoted text
> 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,

quoted text
>

> --

> FA

--

Joel Roth

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