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I have an older Intel i3-540 machine running 16.04 with two audio devices: Device #0 is HDA Intel played through HDMI. Device #1 is a CS46xx (via an old Turtle Beach sound card). The HDMI audio is used by Kodi. The other audio device is used by a separate audio player and goes to other rooms. I'm seeing normal CPU usage when either of the audio devices is in use but unusually high CPU usage when both are in use.

At first, I thought Kodi might be the culprit since it recently upgraded to v17. But I can reproduce the problem with two instances of mpg123 (Kodi not running) which perhaps suggests that the problem doesn't depend on a specific client. Here's a quick rundown of what I'm seeing:

  • one client targeting either device --> 'pulseaudio' process sits at 3-5% CPU
  • two clients, both targeting the same device (either #0 or #1) using pulse's muxer --> 'pulseaudio' process sits at ~5% CPU
  • two clients, clientA targets device #0, clientB targets device #1 --> 'pulseaudio' process jumps to 100% CPU until I kill one of the clients.

Since I can play audio through each device individually without any anomalies it suggests that this isn't a problem with the low-level audio drivers. The only time things go sideways is when both audio devices are active. I've tried the "tsched=0" trick with no noticeable improvement.

Is there a known problem getting pulseaudio to play nicely with two or more audio devices?

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