Hello Lorenzo, > I have anecdotally, but recurrently observed on laptops - including a > rather recent one - that there is always a 'best' USB port for external > sound cards. > > For instance, on my latest machine with a decent 'realtime audio' > configuration/set-up (real-time kernel, /etc/limits stuff, 'performance' > CPU governor, (wireless) network switched off), I'm able to have a > pleasant xrun-free session recording in Ardour including a bunch of > tracks with effects playing at 64 frames and period of 3 with a > relatively cheap card (UMC202) on one of the USB ports. > On the other hand, in the exact same conditions I get incidental xruns > at even 128 frames and xrun instability at 64 frames on the other USB > ports. > > I wonder: > > 1. Is there a more scientific (well, precise at least) method to assess > this USB port performance? What to test or look into? You can check with lsusb what sits on which bus and if your soundcard sits on the same bus with a device that could interfere (Wifi, Bluetooth) then either try moving it to a different bus or try freeing that bus. A bus is not the same as an USB port, multiple USB ports could be hooked to the same bus. > 2. Is there a way to change (e.g. improve the not-so-good USB port > performance) OS/software wise, or is this usually hard-wired in notebooks? You can prevent kernel modules from loading by blacklisting them or even unbinding them: https://autostatic.com/2013/12/29/resolved-jack-issues-on-notebook/ > 2a. Are IRQs relevant on laptops and if so can a whole USB port (or > the device attached to it) be optimised from the OS? Yes they are and they can be optimised if you use threaded IRQ's (i.e. hardware IRQ's that have a software counterpart). There is useful info about that on https://wiki.linuxaudio.org/wiki/system_configuration > Of course I _can_ live with one 'good sound-card port' on a laptop but > I'm quite curious about people's experiences and the gurus' wisdom - > albeit on my former machine this was the left-side port which was closer > to where the sound-card usually sits, now it's on the right, too bad! > > Hopefully other LAU have mused about such USB-related mysteries in the > past... Well I have so if you'd like to improve your current situation I might be able to help out. Jeremy
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