Created attachment 128302 [details] aplay and pactl list cards output When using a TB15 dock on an XPS 13 (9350) the front output works fine but the output in the back of the dock is not accessible by pulse audio. alsa finds the card and the two devices fine. In the attached aplay -L and pactl list cards output you see USB Audio #1 listed correctly and playing a sound to that device via aplay plughw:1,1 works fine but pulseaudio does not seem to create an output for it. pavucontrol lists the USB device but its only the front output (which is designed for a headset).
PulseAudio uses alsa devices like "front", "surround51" etc. The "hw" devices are only used when nothing else is available. In this case I guess the "front" device is available, so PulseAudio uses that, but it refers to "hw:1,0", while you'd like to use "hw:1,1". To make PulseAudio use "hw:1,1", custom configuration is needed. Here's some documentation for that: https://www.freedesktop.org/wiki/Software/PulseAudio/Backends/ALSA/Profiles/ A proper fix would require adding some new functionality to alsa so that PulseAudio could automatically figure out that there are separate PCM devices for headphones and speakers.
Does this mean that if I can figure out how to get alsa to create a "2nd" PCM that it would bubble up to the pa level correctly?
No, there already are 2 PCM devices, hw:1,0 and hw:1,1. I meant that alsa should somehow provide information about what hw:1,1 is (and then pulseaudio has to be changed to use that information). It's not a good idea to blindly create sinks for every hw device. For example, the "surround51" device may actually use multiple stereo hw devices, but pulseaudio doesn't know what the relation between "surround51" and the hw devices is.
Ok...I'll attempt to work through the directions in the link. I've gone through it a few times and eventually the "mapping" between udev to profile-sets to paths will make sense. I kind of get it but the "string labels" that map these files together are a bit confusing to me. I'm not sure I have a good mental model of cards, devices and ports but I'll play around around with it.
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