[LAU] Arch Wiki Professional_audio

[Len Ovens]

On Thu, 30 Mar 2017, Ralf Mardorf wrote:

> On Thu, 30 Mar 2017 11:07:35 -0400, Robert Edge wrote:
>> Latencies between 1ms and 5ms are ABSOLUTELY wide spread values in pro
>> audio.
>
> Not in my experiences, but ok, then we simply don't remove it from the
> Wiki. Should we stay with the Wiki as is, or are there at least a few
> other points we should edit?

Then people should be aware that using most USB audio interfaces on a PC 
originally made for windows is not a pro audio solution... at least not in 
a plug and play manner. Loading Linux on such a box will allow one to 
trouble shoot at least and adding an extra USB card in the right slot on a 
mother board without too many bells and whistles (always choose a MB with 
the full 7 slots to give lots of choices). So yes things can be tweaked to 
do well but in the end PCs are designed by people whos concept of "low 
latency" is 30 ms.

Also remember latency as given by qjackctl is only one way through jack. 
It does not include latency introduced by the ADC/DAC for example. My 
Delta66 spec is 1ms through the ADC and internal mixer either direction 
(no I haven't measured it). This means that even though I can (if I hold 
my mouth right) get it to run on jack with 16/2 (qjackctl calls this .66ms 
at 48k) the actual round trip time (mic to speaker) is at least 3.5ms. 
Very few audio interfaces can run at 16/2 though 32/2 is more common 
(> 4.66ms). When I say "can run at" in a pro audio context that means no 
xruns. So special kernel, cron off, hyperthread off, audio IF has it's own 
irq, no wifi, non-intel USB port (if using USB IF), stable cpu speed, no 
pulse-jack bridge...

In any case, in the Linux world as represented by the emails in this list 
and the few irc channels I watch, 64/2 with a round trip latency of over 
5ms (7.33ms on the delta44/66/1010 for example and I have a USB no mixing 
IF that claims .65ms codec delay so 6.65ms) is about the lowest people 
seem to achive in a stable manner. Many people run 128/2 and at least one 
of my internal HDA (not pro at all) will not run jack with 64/2 at all 
(jack crashes).

PCs are not designed for low latency audio, getting it means selecting 
each part of that PC with care and a willingness to buy another if the new 
one you just got has a problem. PCs are designed for high throughput and 
really so is the generic Linux kernel.

--
Len Ovens
www.ovenwerks.net