Dell XPS microphone issue (Linux)

While most HW devices work right out of the box, the "lesser used" ones still provide some surprises. Using a recent Linux kernel the microphone will directly be recognized, still doesn't work, though.
Resolution: Using Alsa, change the "Digital Input Source" to "Digital Mic [1]". You might need to turn up input volume. This has been tested with an Intel HDA SigmaTel STAC 9228.