[LAU] latency - was - what is happening with RT kernel development?

[Len Ovens]

On Sat, March 30, 2013 3:33 pm, Brent Busby wrote:
> On Fri, 29 Mar 2013, Kaj Ailomaa wrote:
>
>> As long as you are not doing software monitoring (i.e. listening to
>> what you are recording through Ardour, while recording it), you don't
>> need low latency at all, and might not need anything beyond
>> linux-generic.
>
> Is this true in all cases, even when using plugins and soft-samplers?
> What about if you're sending some of your audio outboard through a mixer
> for processing in the hardware world?
>
> The reason I ask is because I am doing monitoring in hardware on an RME
> Multiface II, but I'm also sending some channels out to a mixer and
> bringing them back.  Also at the same time I'm using plugins.  I've got
> my Jack latency setup to show up in QJackCtl as about 5ms, but it'd be
> nicer for the computer if I could use a bigger buffer and not worry
> about it.

No matter what kernel you use, a hardware/bios audit makes a difference. I
have done better with just a low latency kernel after tweaking HW, and
bios than I ever did with an RT. (usable audio at 1/2 the latency with
moving the card to a slot with a free irq, another 1/4 the latency with
turning hyperthreading off, yes that is 1/8 all together from 128 f/p to
16 with guitarix running on top in a 10 year old 2.4Gh P4) Turning off
unneeded system services and unloading the kernel modules for unneeded HW
where the bios doesn't allow that also helps. For recording I also use a
higher latency than for live work. Things like ardour are pretty good at
compensating for latency from playback as compared to record. A softsynth
though also delayed before you hear it Is still in time with the audio
track by mixdown and in time with the delayed playback audio for tracking
against. Using outboard HW to modify sound to rerecord would depend on
what kind of modification, delays would not be a problem so long as the
direct sound was not part of it. Real time effects like eq or compression
would be ok for rerecording to it's own track where it could be aligned
before mixing. (I personally do not have any outboard equipment that is as
good as what I have for plugins, your lucky)

I don't know If I have covered your particular use, so the best answer is
to try it and see. If there are problems think if there is a way to fix it
without lowering latency (so long as it isn't more work than it's worth )
and then lower latency until it works.

I try to track with no effects or just use effects for monitoring at a
lower latency (64 or 128) and then move the latency up for mixdown when I
add effects.


-- 
Len Ovens
www.OvenWerks.net