LT RT encoding

I have to encode a 5.1 mix for a film into LT RT. I have never done that before, and it does not seem to work.

I have the 5.1 mix as 6 separate files. I have created a new session and then import all the files to 6 different tracks. I created a 5.0 output and deleted the lfe. So the remaining 5 tracks I route to the correct output on the 5.0. Then I insert the Matrix Encoder in the 5.0. I get a good sounding stereo file.

Now I want to reverse the process. I create a session with an LRCS output. I import the stereo encoded file and put the decoder in the LRCS output. What I hear now is a mono file. What am I doing wrong?

Best wishes,


A sorry, I see what I did wrong. It is working now.

Hi Max,

Please correct me if I’m wrong on this…but to my knowledge you have built an LoRo fold down.
A true LtRt process to the best of my knowledge is only used for TV broadcast, not for a theatrical film release.
And not too often anymore.
If you need to do this from a surround mix, you must use a Dolby approved processor.
You might need to double check with your client if LtRt is really what they want.

A few times I was facing similar requirements, I’ve always done a separate regular stereo mix.
That works, always and reliably.

best of luck…

Hi Andrew,

thanks for your reply. I never had to deliver an LT RT conversion. So far, it always worked without it. It seems to be an old format. But yes, I first thought I need a Dolby E converter to produce a real LT RT. But the Matrix Encoder does give me a stereo file that can be decoded into LCRS. So it seems to work. But I will definitely give them a normal stereo mix as well.

Best wishes,



No, that would not be a Dolby E converter.
For a compatible LtRt down mix you would need this :

There might be other software …

Ok, interesting. But the manuel of the Matrix Encoder says that the encoded file is compatible with Dolby Pro Logic, that it is essentially an LT RT encoding. I interpret this to mean that a Dolby Pro Logic decoder can read and decode the file.

Well Max,

look through this older thread and get more confused :

I still suggest the discrete stereo mix ( remix ?) or look into the DCP variant for theatrical release.
Sorry man, I only do TV.

Interesting. Someone there suggests that MixConvert can do a proper LtRt export. I wonder how that works.

First of all, (haven’t read through the whole thread), be sure that you know what the final format is.
If it’s FILM, that it can very well be a Dobly SR that they need.
As an analog alternative/safety for the Dolby DD readout.

if it’s for TV, then you have to ask what they want.
Lt_Rt, Dolby Pro Logic, Dolby Pro Logic II?
You need to aslkk for what it is going to be used.

Most of the specs include a Lt_Rt mix, but that is mainly because these specs have always been there, and nobody knows why they are still part of the specifications.
I make a sport out of it to ask them these questions, so they have to inform themselves at the technical department.
Result: Haven’t made an Lt_Rt since years.


Thanks Fredo! That is very helpful. It is definitely not film. I will ask them. It looks like an old specs sheet.