What is the difference between dolby 5.1 and dolby digital, other than the digital aspect. Are the rear channels the same signal but different volumes in 5.1, or are the completely discrete? What about dolby digital? How is THX different?
In DD 5.1 the rear channels are discrete.
Also THX is not another type of sound (like mono, stereo, dolby, dts etc…) but rather a set of guide lines for setting up sound systems in theaters. Goto www.thx.com and you can take a look at them.
Dolby 5.1 is a type of Dolby Digital. Dolby Digital can have anywhere between 1 and (I think) 5.1 discreet channels, the .1 referring to the Low Frequency Effects channel.
As to the “I think” part, I’ve never seen a Dolby Digital track with more than 5.1 discreet channels. Sure some DD has six channels plus LFE, but the center rear channel is derived from the two surrounds and not actually a completely seperate channel.
Another method of having multichannel surround at home is DTS. I don’t know the technical differences between DTS and DD other than the DTS track on a DVD (if it has it) usually (always?) has a higher bitrate than the DD track on the DVD. Also, DTS can have at least 6.1 discreet channels, possibly more.
There are also Dolby Pro-logic which isn’t used much anymore, and DPL II which I’ve only ever seen used in Gamecube games. I’m not sure how they work, but they take two channels from the source, and turn them into four in the case of DPL (it has mono surrounds) and five in the case of DPL II.