[Ardour-users] WAV files, xruns
orders at nodivisions.com
Fri Feb 20 19:42:58 PST 2004
Jack O'Quin wrote:
>>So can I tell what latency I've achieved based on those numbers? I've
>>seen people on this list say, "I get X ms latency," etc. Is there a
>>formula? I assume it's something divided by the sample rate (in kHz)
>>in order to get a result in ms.
> Right. Check `man jackd'...
> -p, --period int
> Specify the number of frames between JACK process()
> calls. The default is 1024. If you need low
> latency, set -p as low as you can go without seeing
> xruns. A larger period size yields higher latency,
> but makes xruns less likely. The JACK input
> latency in seconds is --period divided by --rate.
> -n, --nperiods int
> Specify the number of periods in the hardware
> buffer. The default is 2. The period size (-p)
> times --nperiods times four is the JACK buffer size
> in bytes. The JACK output latency in seconds is
> --nperiods times --period divided by --rate.
= period / rate
= 2048 / 48 kHz
= 43 ms
= n * period / rate
= 2 * 2048 / 48 kHz
= 85 ms
So that's pretty bad, right? Since I see docs saying that latencies of 2ms
are possible? So it's a tradeoff between high(ish) latency, and xruns.
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