On Mon, Sep 23, 2019 at 01:14:04PM +0200, Lorenzo Sutton wrote: The one thing I can think of is to use lsusb to see if the USB bus the card is on is shared with other devices (which could be internal). Ciao, -- FA

On Mon, 23 Sep 2019, Lorenzo Sutton wrote: Surprise! I have had this experience too. In my case, I had two sockets on the right and one on the left. It was not a matter of one was better than the others, it turned out I could use either of the right hand sockets for my audio device... so long as the other was empty. So I had to add a USB hub to the left side for everything else. The way to look for a good port is to start by finding out which USB bus each of your sockets go to and what buses are already being used. The tool for this seems to be usb-devices. All computers I have looked at (by no means everything) have on each bus a controller and a hub internally. That is ok. So plugin something in each port, one at a time and run usb-devices to see which bus it ends up on. It is also a good time to check what other things may be using that bus internally. So for Audio work you want to use one of the buses just for your audio device. IRQs can be checked with: cat /proc/interrupts The first number is the IRQ and the last is the process using it... or the processes using it. If you are lucky you will see something like: ehci_hcd:usb1 and that will tell you what bus uses which irq each bus uses. You can then use rtirq to raise the priority of that bus in the line: RTIRQ_NAME_LIST="rtc snd usb i8042" rtc and i8042 need not be there allowing just the usb in there may be counter productive as well because then rtirq raises all the usb buses up and may put your mouse on a higher priority than youe audio. Better to leave them alone in that case. However, if you can see the bus on: ps ax (ps ax |grep usb1) then you can change that line to: "usb1 snd usb" and that will allow your audio device to have a higher priority. However, newer kernals and newer mother boards are different. (and not even that new) My desktop as it came insisted that my usb audio device was on bus 3 no matter which socket I used. It did not matter if they were USB2.0 or USB3.0 sockets but it would internally route them all to the same socket... till I went into the bios and turned the xhci controller off. Now I have two buses (I had four before with only one ever getting used) that say ehci and only bus 1 and 2. Rtirq does not find usb1 separately from usb2 still but there is udev-rtirq: https://github.com/jhernberg/udev-rtirq and that sets it just fine dynamically. turning xhci off means no usb3.0 use... but I am ok with that. (I have no usb3.0 bits anyway) Adding a USB PCIe card would give me it's own IRQ even with xhci but that is not a laptop solution. Things I don't know: I think my cheap USB audio device is actually USB 1.1 and not usb 2. A USB2.0 device may grab one of the ehci controllers even with xhci running, I don't know. A USB3.0 hub plugged into a USB3.0 socket may use one of the other usb buses besides the one xhci wants to use for everything usb1.1. As a side note, USB has never been about latency. Rather the opposite if anything. The advances in USB have been speed or throughput. Latency is not even the same from one run to the next. In USB there are no guarantees... but in low latency, guaranteed schedualing is what it is all about. USB audio devices means getting things sort of good. With a laptop that is about as far as things go. -- Len Ovens www.ovenwerks.net