[Ardour-users] WAV files, xruns

Jack O'Quin joq at io.com
Sat Feb 21 10:14:28 PST 2004

Anthony DiSante <orders at nodivisions.com> writes:

> Input latency
> = period / rate
> = 512 / 48 kHz
> = 11 ms
> Output latency
> = n * period / rate
> = 2 * 512 / 48 kHz
> = 21 ms
> It's not 2ms, but it's considerably lower.

For most purposes these latency numbers are probably fine.  Low
latency is not an absolute goal.  What you generally want is the
highest latency that is "low enough" for your system to feel

This is subjective and depends on the kinds of applications and types
of input you use.  A soft synth needs rather low latency when
responding to MIDI commands from a keyboard.  Otherwise it feels balky
and unresonsive to the keyboard player.  In this case, a high variance
in the latency is even worse than a steady but longer delay.

For recording, you typically only need or want low latency when you
must monitor the material being recorded through the computer.  Often
that is not necessary, in which case you should probably record at
higher latencies to reduce the probability of xruns.

> Also... it seems interesting to me that if I use a lower sample rate,
> the latency goes up.  It would seem more intuitive to me that if it's
> sampling less often, working less hard, the latency would improve (go
> down).  But no? Where am I going wrong?

There's more time between frames, so a fixed number takes longer to
capture or play back.  Typically, the system can run with a
proportionately smaller period size if the sample rate is lower,
unless your card places restrictions on that.

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