[Ardour-users] WAV files, xruns

[Anthony DiSante]

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.

So...

Input latency
= period / rate
= 2048 / 48 kHz
= 43 ms

Output latency
= 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.

-Anthony
http://nodivisions.com/