Could someone explain the difference between Dolby Digital and Dolby Digital 2

I think you mean Dolby Pro Logic and Pro Logic II. Both Pro Logic and Pro Logic II are designed to use a stereo signal (left and right channels only) to produce some form of surround sound (adding a center and surround speaker channels).

Pro Logic is the old surround processing that was based on a stereo analog signal into which a center channel and a surround channel (mono, with both left and right surrounds getting the same signal) were "matrixed" so that a Pro Logic decoder could extract them. When given a true stereo signal (i.e. a signal that was not originally intended for Pro Logic decoding), the Pro Logic decoders often had a hard time getting much out of the signal -- it would sometimes collapse entirely to the center channel, for example.

Pro Logic II is a new form of decoding intended to work with a stereo signal. It can still handle Pro Logic soundtracks, but it can also work well with purely stereo soundtracks. In many cases, Pro Logic II decoders include two modes -- one for movies, and one for music. Also, unlike the original Pro Logic, PLII produces a 5.1 channel output (discrete left and right surrounds and a subwoofer channel) and a full-range signal to all five channels (Pro Logic's surround signals did not cover the full 20Hz-20,000Hz frequency range, and I don't remember if the center did). Basically, Pro Logic II gets closer to the sound of Dolby Digital soundtracks than Pro Logic did. You might be interested in this link to Dolby's site .

Dolby Digital, by the way, is very different from these two. It is a digital format, with five discrete full-range channels (left, right, center, left surround, and right surround) and a ".1" low frequency effects ("LFE") channel. There is an extension of Dolby Digital called Dolby Digital EX that adds a surround back channel (one or two speakers at the back of the room) that is matrixed into the surrounds, much the way the Pro Logic matrixed in the center and surround channels.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

an EXCELLENT response, gonk! a very clear explanation.

The Gonkster never fails to come through.

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Matthew J. Hill
matt@idsi.net

I'm pretty sure DD is also out there in a 2.0 format, basically the audio is stereo/DPL but the data stream is encoded with the AC-3 algorithm.

I think. Right?

Yup, 2.0 refers to Right and Left tracks only (stereo) but is encoded in the AC3/DD signal format. You see that as well as DD Mono often with older movies where they have been unwilling or unable to re-master the audio tracks.

Dolby Digital can, I believe, include any number of tracks less than or equal to 5.1 -- so you can have Dolby 2.0 tracks (stereo, left and right channels only), Dolby 1.0 (mono), Dolby 4.0 (left, right, center, and mono surround), Dolby 5.0 (all channels but no LFE channel), or whatever.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

This is true, I think, except that it always has two tracks. Mono is encoded as two identical tracks.

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Matthew J. Hill
matt@idsi.net

Really? Any idea the reason behind that? Are they both decoded and played simultaneously through the center channel? Any insight how that works?

I'll have to look, but I just picked up a bunch of Eastwoods Italian/Westerns (GB&U,Fistful, etc) and they are mono, center only. Thought they were DD.....

Charlie