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_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.