I just installed a graphics card (lspci says Radeon HD 3450) with an HDMI port so I can use 7.1 surround with my audio receiver (after finding out SPDIF/TOSLINK/"Optical audio" doesn't go above 5.1) and it works.

Well, it works fine in stereo. I have the options in PulseAudio, so I assume it's supported:

  • HDMI Stereo
  • HDMI Surround 5.1
  • HDMI Surround 7.1

But when I switch to 5.1, the sound is slowed to a low speed and pitch, even slowing down video playback along with it.

And when I switch to 7.1, the sound is comically slow. Pitches are distorted to high screeches and low moans.

But unlike the other issues I've found when researching this problem, sound does still come out, in each case over HDMI. I can always switch back to Stereo and I get good audio again, but I want 7.1, obviously.

Speaking of which, here's something that might be a hint: my receiver says LINEAR PCM 2.0 Ch [48kHz] when sound plays (such as watching Big Buck Bunny) through Stereo mode, but it also says exactly that when PulseAudio is set to either Surround mode.

That shouldn't be the case, when I used the optical audio cable, 5.1 audio showed up as 5.1 audio. But it makes sense, because the distorted death noises also seem to be coming out in stereo. (Source is surround-enabled movie.)

In summary, when the output should be adding additional speakers to the mix, it just slows the stereo sound down and distorts it instead.

Any suggestions? I've tried:

  • Upgrading Ubuntu (Xenial all the way to Artful 17.10)
  • Restarting, of course (a zillion times)
  • Restarting PulseAudio
  • Force-reloading ALSA
  • Upgrading to the latest daily DKMS deb for ALSA (reportedly fixes a (similar bug)1)
  • Speaker-test and aplay as well as different audio players like VLC and Kodi

PulseAudio is not normally quick to offer unsupported modes (in fact it more likely withholds modes that should be there) so I'm guessing (hoping) it's not just because the graphics card can't do it. I haven't tried the proprietary graphics driver (I'd rather not) but I heard it supports less features anyway.

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