2.0, 4.0, 5.1 matrix and downmix confusion

someone wrote:

> My exact words were dpl is a 5.1 matrix.  I NEVER SAID it was derived
> from 5.1.  That simply meant, in its best form, THX, there is a derived
> matrix of 5.1 channels.  DUH!  I should have put in THX instead of DPL.
> The soundtracks, pre AC-3 that were THX, were mixed specifically for a

Actually DPL (Dolby Pro-Logic) or Dolby Surround is considered a 4.0 matrix. A 2.0 stereo pair, also called Lt Rt, can be matrix encoded, there is no such thing as a "5.1 matrix". I know what you meant and my gripe is just a misuse of terminology. For those who want to read more about Dolby surround I recommend the technical articles at http://www.dolby.com/

Also many DVD's are being released as having 5.1 tracks, but in fact they from 4.0 master tapes. This is confusing to the consumer. Listen for the mono surrounds or check with a SPL meter if the adjusted bass (SPL meter + (0dB - your volume)) is much greater than 105dB and closer to 115dB. This will tell you if they are using a LFE channel.

Basically any format of channels can be turned into any another format, many cases with information loss. You can of course go 5.1 --> 2.0. But that is called "down mixing" 5.1 into 2.0 and every DVD player does this!

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