SMPlayer: sound but no voice; MPlayer is OK

[Schrödinger's Cat]

On some videos only, I get some sound (incomplete music and effects) but no voice. In regular mplayer, it works fine, but not in SMPlayer, VLC, or xine, and only with some files. Other files play normally under the same circumstances.

I've tried going through the entire list of Output drivers in SMPlayer, but to no avail.
- alsa gives no sound at all, alsa 0.0 produces a horrible screetching sound; 0.3, 1.3 produce no sound
- sdl gives a really weird effect: it produces the proper output but the voice cuts in and out with seemingly no rhyme or reason... like streaming audio on dial-up
- pulse is what the player loaded by default, and it produces the sound-but-no-voice problem
- all other output drivers produced either no sound, or sound but no voice.

Again, mplayer works fine, so there's obviously a settings problem in SMPlayer but darned if I can find it! Prior to this problem, the only things I've changed in settings are related to keyboard and mouse controls. As I understand it, SMPlayer is basically an interface for mplayer, so this is really confusing me.

Thanks for the help!