[LAU] [solved] Focusrite 18i20 balanced -> unbalanced

Len Ovens len at ovenwerks.net
Fri Jan 20 15:49:48 UTC 2017

On Fri, 20 Jan 2017, Ralf Mardorf wrote:

> With linux 4.9.0-rt1 it's possible to go down to 32 frames at 48 KHz,
> getting lots of inaudible xruns, at 16 frames as well as 64 frames the
> interface is completely unusable. At 128 frames it's the same as for a
> vanilla kernel with threadirqs, just scrolling with the USB mouse wheel
> in roxterm usually does cause issues, very seldom a random xrun could
> happen, when switching to another window. At 256 frames it seems to be
> absolutely stable, however, it seems to be usable at 128 frames, with
> linux-rt as well as a vanilla linux with threadirqs. FWIW using another
> USB cable at 128 frames doesn't make a difference. Actually it even
> seems to be usable at 32 frames, the xruns were inaudible. I don't know
> why it's completely broken at 64 frames. 16 and 64 frames cause long
> interrupted audio signals.

16/2 is less than 1ms at 48k... 16/3 at 48k is 1ms, maybe try 16/3, 32/3, 
64/3 to see if that works better (at 48k) as they are all multiples of 
1ms. It seems to me USB does things in 1ms intervals. (this is all based 
on rumours and conversation bits I recall... not hard knowledge on USB)

Len Ovens

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