Will an LTRT mix playback as stereo if the sound system doesn't support surround? Would that make it redundant to have say an LTRT mix on channels 1&2 and a backup Stereo mix on channels 3&4? Also, do you have to pay Dolby to create an LTRT mix and what is the price difference between that and 5.1?

Q. Will an LTRT mix playback as stereo if the sound system doesn't support surround?

A. Yes. It is indeed a stereo non surround track. The Lt Rt name means it is derived from a surround project, where the rear and centre and sub (and therefore audio with no natural home in the stereo image) is re distributed by the dolby encoder correctly ion terms of level and position.

Q. Would that make it redundant to have say an LTRT mix on channels 1&2 and a backup Stereo mix on channels 3&4?

A. Yes ( and very misleading to the recipient. Put Stereo ONLY on 1 and 2 or if its surround then Lt Rt on 1&2 and Dolby E on 3&4, but no duplicating of effectively the same thing.)

Q. Also, do you have to pay Dolby to create an LTRT mix and what is the price difference between that and 5.1?

A. You dont pay Dolby, but the mix needs to be a discreet 6 ch mix and then it passed through a Dolby DP570. This creates the dolby E (Encoded 2 track 5.1 material for decode) and the LtRt mixdown too.
The price is dependent on the studio you get to do it.
Although if its for Film and is to carry the Dolby logo etc etc then it MUST be mixed in a dolby accredited mix room.

Beware this is a really specialized area as there are loads of Metadata and dial norm settings to be assessed and Id strongly recommend a professional who does theis every day rather than jumping in, buying the gear and having a go.
Getting sued by a client is never pleasant.

Peter
dubbingmixer