Analogue sound on RPi ARMv7

I take a Pi on holiday to use with a VGA monitor via an adapter and use the analogue headphone socket to drive some “PC” speakers.

With my earlier RPis the usual command in the CONFIG.TXT file
  hdmi_drive=1
works fine to switch the sound output to the headphone socket, but doesn’t seem to work at all with the ARMv7 Pi2 which I’ve brought with me this time.

Eventually I found a solution to the problem by replacing that line by
  hdmi_ignore_edid_audio=1
which, according to RPiconfig, pretends all audio formats are unsupported by the display. This means ALSA will default to analogue.

When I get back home to my HD monitor I will revert to
  hdmi_drive=2
to send the sound once again to the monitor

I am sharing this in case anyone else has the same problem.

Hi John,
Thanks for sharing this. It will save me some confusion if I demo RDSP on a Pi 3.
Tony

With my earlier RPis the usual command in the CONFIG.TXT file
  hdmi_drive=1
works fine to switch the sound output to the headphone socket, but doesn’t seem to work at all with the ARMv7 Pi2 which I’ve brought with me this time.

I wonder if this is because I have a CMDLINE.TXT file setting disable_mode_changes? Could it be this which prevents the hdmi_drive=1 working as normal, or is it actually a Pi 2 thing? I may experiment when I get back and have more m/cs to play with.

I have RC15 on my Pi 3, with no CMDLINE/TXT file. Sound works out the headphone socket with a more-or-less default CONFIG/TXT. The only HDMI-related change is there is hdmi_blanking=1, which shouldn’t affect sound. I do not have an hdmi_drive line in there.

The same configuration worked on my Pi 1.

I have RC15 on my Pi 3, with no CMDLINE/TXT file. Sound works out the headphone socket with a more-or-less default CONFIG/TXT.

Thank you Chris. Perhaps Jeffrey might care to comment on any effects on analogue sound that disable_mode_changes might make?

I believe it’s a change in the firmware which has affected the behaviour, rather than the addition of GPU mode change support. I too have hdmi_ignore_edid_audio in my preferred config.txt, although I can’t remember exactly when I added it. Some experimentation reveals the following:

• With a Pi 3 connected to an audio-capable HDMI monitor, the default is for the audio to go via the monitor
• “hdmi_drive=1” forces the Pi to drive the monitor in DVI mode (preventing the audio from being sent), but because the audio descriptor is still present in the EDID the GPU appears to get confused and still tries to use HDMI audio. So the end result is that you don’t get any audio at all.
• Removing “hdmi_drive” and replacing it with “hdmi_ignore_edid_audio=1” tells the Pi to ignore the audio descriptor, so it falls back to using analogue audio
• The above three steps produce the same result whether disable_mode_changes is enabled or not.

I believe it’s a change in the firmware which has affected the behaviour, rather than the addition of GPU mode change support. I too have hdmi_ignore_edid_audio in my preferred config.txt

Thank you for the clarification.

OK – summary:

Firmware has changed, and the way of ensuring sound via the jack socket now is to include the line:

  hdmi_ignore_edid_audio=1

in the CONFIG.TXT file.

Commenting this out with a hash (#) reverts to “normal” behaviour where the sound is sent via HDMI.

The old  hdmi_drive=1 or 0 line is no longer relevant to sound output.

I hope that this will help future users.

My earlier post probably added to the confusion. I forgot that I was using an HDMI-to-DVI cable so there’s no audio support, which is probably automatically pushing the Pi to use the analogue output. That makes sense considering the fix.