I've been trying to create a mono AAC file with FAAC but I always end up with a stereo encoded file. Is it possible to create mono files with FAAC? I've tried feeding it mono wav files but it always turns out stereo and I can't seem to find a switch for mono encoding with --help. Any ideas?

the chance, that your encoded files indeed are "mono" is quite good

FAAD based players just decode them as "stereo"

Use fb2k player "Downmix channels to mono" DSP

The files are probably indeed mono. FAAD2 based players (almost all of them) decode any mono file as stereo. This is so that the players using it will correctly handle HE-AAC v2 without any special changes.

Thanks guys.