so when i have my PS2 plugged in via the optical in and my receiver says PCM and only the left and right speakers are playing, but i have it in dolby digital mode, does that mean that it is playing true 5.1 sound?
i was playing need for speed underground when i noticed that there was ambient sounds coming from the rear and that the center was providing most of the sounds but it only said PCM and said that left and right speakers were playing.
If your receiver is listing PCM, it most likely isn't doing 5.1. PCM is usually displayed when the receiver is getting a stereo signal from the source, i.e. the PS2. If the game supports 5.1 audio, you can enable it by going into the PS2 setup and telling it to output Dolby/DTS. All the game consoles that support Dolby/DTS default to PCM stereo unless you specify Dolby output.
It's almost certain that what's going on is that your PS2 is providing a 2 channel PCM signal (PCM is always 2 channel, maybe mono - not sure) and your receiver is doing some Dolby ProLogic processing. If you see DTS logos then it might be doing DTS NEO:6 surround processing. Anyway, with ProLogic and NEO:6 you often find that most of the sound comes from the center channel and the left and right mains are often quiet. If it were a true DolbyDigital 5.1 signal entering your receiver you'd probably get a more even split of music and sound effects in the mains while the center would be used mostly for dialogue.