[LAU] Focusrite Saffire Pro 40 - reliable?

[Len Ovens]

On Sun, 1 Mar 2015, Robert Jonsson wrote:

> 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?

I should add a bit about FW/USB cards. This is just general stuff. It 
seems that there is a lowest point jack will even start latency wise:
ice1712 - 16/2
ens1370 - 32/2
fw	- 32/2
USB	- 64/2
Intel HDA - 64/3

These seem to be based on the size of the HW buffer in the IF itself 
and/or the bus protocol in use. AES67 suggests 16/3 (1ms) and I suspect 
both FW and USB may bennefit from /3 as well after reading the AES67 
reasoning for 3 buffer use.

Anyway, all of the things I do for a PCI audio IF, I would also do for the 
USB or FW host card. In a desktop machine, I would tend not to trust any 
onboard FW or USB hosting, choosing rather to buy a PCIe card and treat 
that card the same as I would a PCI(e) audio card. I have found with USB 
audio IFs that when setting up /etc/default/rtirq it is best to single out 
the USB port I am using for sound. So rather than ordering things:

RTIRQ_NAME_LIST="rtc usb i8042"

I would order things:

RTIRQ_NAME_LIST="rtc usb3 i8042 usb"

Where usb3 is the USB line I use for audio. This allowed for stable 64/2 
use on my netbook with a USB AI even running the single core Atom at 
800Mhz (half speed) over 8 hours or more with no xruns. (audio use only)

Also it occurs to me... swappiness 10... and make sure to have enough 
memory that no swapping ever takes place  :)  An unimportant thing like a 
workspace pager that gets swapped out... can stop audio dead if the user 
has the soft synth on a different workspace they need to adjust. I love 
having two screens and would gladly add more. I use workspaces much less 
than I used to. Swap in audio has only one use... every thing is saved 
even if the take is ruined by swap. OOM events can just kill everything as 
the DE seems to be the thing that gets kicked out :P

--
Len Ovens
www.ovenwerks.net