foobar2000 plays mono as mono on center channel.
Thanks Case . I guess that explains it- I don't even have a center speaker connected. I'm just listening with normal headphones btw.
Yeah I had already figured out that using the "mono to stereo" DSP cured the problem, but was unsure why it was necessary. I was trying to figure out why it couldn't just play mono correctly in the first place.
Still wondering if it's wise to assume that someone has a center channel connected, just because they want to play a mono file. I've got a about a million programs on my PC that can play a wav file, and all other 999999 play it without any fuss.