[LAU] Trying to record!

Len Ovens len at ovenwerks.net
Thu Jan 10 03:42:43 CET 2019

On Wed, 9 Jan 2019, Bob van der Poel wrote:

> Hey, me again. Back at it ... same problems :) But, I _think_ I figured out the
> problem ... it's the USB port. If I use the "easy to get at port", I'm using a
> USB3, and it creates the problem. If I use a harder to reach port, USB2, all
> works fine. Don't need to use pasuspender, don't need to turn off pulse audio
> ports, etc. Just run audacity and it all works.
> To recap, I'm using a Presonus Audiobox USB connected to my PC and running
> Audacity to do some simple recording. The USB3 port gives me scrambled recordings
> ... the USB2 port works fine.
> So, do I have a bum port or is this normal?

Totally normal., Most mother boards do this two ways:
 	- one of your USB ports is probably connected to IRQ16 for legacy
 	purposes, along with two or three other internal bits.
 	- even if that is not the case, it may have an internal hub and be
 	sharing that port with another physical USB plug (with your
 	mouse?) or even an internal mic or whatever.

I had a laptop (netbook?) with one USB on the left and two one the right. 
To get stable sound, I had to use one of the right hand USB ports for 
audio and leave the second right hand empty and put a hub on the lefthand 
side to use with everything else. The lefthand USB was also used 
internally as well as being irq16 while the two on right were from the 
same hub (so I could only use one) but had a clear irq.

Also, some MB have bios settings for irq choosing. It may be possible to 
allow the MB to asign USB or other irqs or not (or leave certain irq 
unassigned). I have found that letting the Linux kernel assign the irq 
rather than bios gives a more inteligent assignment. If you have a desktop 
with spare slots, I would get a PCIe USB card and use that USB for audio 
only... trying different PCIe slots to find the one that works best.

Finally, if you use the rtirq script at boot.... it may seem nice to do:
"usb, snd, whatever" but you may be better doing: "usb2, snd, whatever, 
usb" to make sure that your audio IF is actually higher priority than your 
mouse (assuming you are using USB2 for audio). I have an old ice1712 in a 
PCI slot (yes I found a new MB with 3 PCI slots in it) and so put 
"snd_ice, snd_ens, etc" because my ensoniq sound card can not be before 
the ice or it interferes with it (and I am only using the ensoniq for it's 
MIDI ports).

Some of these tweaks may be less needed if you use an RT kernel, but I am 
using a lowlatency kernel and these kind of tweaks allow me to run the 
ice1712 with jack at 16/2 and no xruns (so long as pulse is not bridged, 
pulse is fine down to 64/2 though... 128 with skype).

Len Ovens

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