[LAU] (Ardour) How to get rid of delay when recording ?

[Len Ovens]

On Sat, 13 Feb 2016, jonetsu at teksavvy.com wrote:

> The system is Linux Mint 17.  A 'ps aux' shows:

sudo apt-get install linux-lowlatency for a start. (I would imagine you 
have linux-generic right now) also install rtirq.

As you are running a delta1010 (I think), sudo edit /etc/default/rtirq... 
the line that says:
RTIRQ_NAME_LIST="something something"
to:
RTIRQ_NAME_LIST="snd_ice1712"

Never run jackd as root. (you may not be able to run as a user after 
wards which, as someone else already said, you have to do in order to use it)

speaking of jackd... if you used Software Centre to install it... sudo mv 
/etc/security/limits.d/audio.conf.disabled /etc/security/limits.d/audio.conf
and probably add yourself to the audio group before loggin out and back 
in. (Software center does not install jackd correctly)

If you have more than one PCI slot, and cat /proc/interrupts shows 
snd_ice1712 sharing an interrupt with something else you might try moving 
it to another slot (sharing with fasteoi* is ok it seems).

people say it is worth while building a true realtime kernel by patching 
the mainline and rebuilding, but I have not done that, I do turn cron off 
while recording though as that seems to help... with a RT kernel that 
shouldn't be needed.

Do change your CPU governor from OnDemand to Performance. Even running the 
cpu at the lowest speed possible (800Mhz normally) seems to work better 
than the faster OnDemand. So if you have trouble with heat (you shouldn't 
as you should not be doing 100% cpu load while doing audio) it is better 
to set the CPU governor to UserSpace and set the speed to a steady lower 
speed where temperature is ok.

Do find out how to change "swappiness" to 10 rather than 60 so the kernel 
doesn't start preemptive swapping even though it is using less than half 
your RAM  :P

If you want to run Jack really low (16/2 or 32/2) it may be worthwhile 
turning hyperthreading off. I have found a difference at those latencies, 
but not at 64/2 which is normally good enough.

That is the short list, I may have missed something.

Finally, the ice1712 based AIs like you have are able to do 1-2ms 
monitoring. If you are hearing delay, you are not using HW monitoring. 
Some of the input signal is going through your recording chain as well. Or 
to put it another way you are not _just_ using HW monitoring. I have made 
this mistake often enough to know :)

--
Len Ovens
www.ovenwerks.net