[LAU] Focusrite Saffire Pro 40 - reliable?

[Len Ovens]

On Sun, 1 Mar 2015, Robert Jonsson wrote:

> Hi Ben,
> 
> 2015-02-28 21:17 GMT+01:00 Len Ovens <len at ovenwerks.net>:
>
>       I can only answer some of these questions. The 1010s will have
>       slightly lower latency. Mine runs at 16/2,
> 
> 
> I sometimes wonder about numbers like these and if I'm doing something wrong or
> if it's incredibly hardware dependent. I've never ever come close to running at
> 16/2 in a stable manner. 128/2 I could run reasonbly stable with the Delta 44.
> Now with firewire it's harder still.
> Do you really get this without xruns? Any magic tricks? How much have you tweaked
> your settings to get there?

- Ubuntu lowlatency kernel
- No hyperthreading
- No Intel Boost technology
- ice1712 card in pci slot with highest number irq
 	(I actually test my card in different slots for best performance)
- not sharing that irq with _anything_ else
- Internal audio disabled in BIOS
- On board Intel graphics to two screens
- Keyboard and mouse use serial ports (mini din)
- CPUs locked to one speed. I set performance, but I have gotten good
 	performance locking the speed to 800Mhz too. Try performance
 	first, but if things get too hot then drop a step. If you are
 	building your own kernel make sure to include "userspace" if you
 	think heat may be a problem. I have run all 4 cores at 100% for 15
 	min. (till temperature stablizes) and am ok with performance.
- /etc/default/rtirq has:
 	RTIRQ_NAME_LIST="rtc snd_ice1712 snd usb i8042"
 	The snd is for the ensoniq card that I use for midi. It has a
 	higher intrinsic latency than the ice1712 and so should have
 	a lower irq as well as priority. I have found I can use the two
 	channels on the ensoniq with zita-a2j with no issues as well.
- I turn off cron while running low latency use. I have an app that
 	does this all together for me:
 	http://www.ovenwerks.net/software/index.html
- Pulse audio does not know about any ALSA devices and is disabled during
 	very low latency work. PA into jack seems to work fine down to
 	128/2, but cpu use starts to climb lower than that.
- There is no WIFI on this machine. My netbook had to have the WIFI kernel
 	module unloaded for xrun free audio (even at 20ms one way latency).

I have also found that telling the mother board _not_ to set irqs while 
booting helps. The Linux kernel seems to do a better job of assigning USB 
irqs with less overlap.

I have done this with two motherboards now. The first was an old P4 
(single core, 2.4Ghz, 2.5Gram... started with 1Gram actually) Where PCI 
slot choice made a very big difference, it is less so with the new one.


I spent some time when I was looking for a new motherboard. I wanted As 
many PCI slots as possible (I have three), I wanted a 4 core i5 CPU 
(hyperthreading is not an issue :) and I wanted the din plugs for both 
mouse and keyboard. The mouse generates a lot of USB traffic on a USB 
mouse.

I get xruns at very predictable times:
 	A jack application starting or stopping.
 	Some Firefox uses.
 	System updates.

There are a few jack applications out there that do not properly shutdown 
their jack ports on exit, these always (at any latency) give xruns. I 
found this out during my fledgling attempts at jack programing.


--
Len Ovens
www.ovenwerks.net