REALLY force Raspberry Pi to send audio via HDMI

Question

I wanted to use my Raspberry Pi with a very old video projector which was not capable of processing audio signals. So I bought an HDMI-audio-extractor (Ligawo 6518725 HDMI Extractor), as the PWM analog audio output had poor quality.

This set-up did not really work from the beginning, because there was no audio output. I was checking all the hdmi_drive=2, hdmi_force_hotplug=1, hdmi_ignore_edid, etc. options in /boot/config.txt. Which didn't help, because the Raspberry Pi did not understand that it should send audio, although the final video signal sink was a "dumb" DVI display.

Answer 1

What finally helped was the following:

• I dumped the EDID-file with tvservice -d edid_dump.bin
• I edited this file with LIGHTWARE-EDID-editor (part of a demo suite).
• What I actually needed to change was little: In the CEA part of the file, I needed to specify that the device was HDMI-compliant (HDMI/HDMI options), and under CEA/Audio data, I needed to add LPCM ("linear pulse code modulation" with two channels, and all quality levels, as the hdmi extractor has two channels only).
• I then saved the file, renamed it to edid.dat and uploaded it to /boot/ (i.e. /flash/ if you are using openELEC) and added hdmi_edid_file=1 to the config.txt. Saved, rebooted, now it worked!