Balancing Stereo and 5.1 Mixing with a Dolby Pro Logic II Stream
When a Dolby Pro Logic II-encoded stream (LtRt) reaches a decoder, there are coefficients in place that will derive channel information from the generated LtRt. The decoder splits this information between the surround channels to create a 5.1 surround mix.
Pro Logic II is a matrix encoder, so there will always be added energy to the surround channels when the LtRt is decoded. The best thing you can do is get the LtRt mix to sound as good as possible while achieving a happy medium between your stereo LtRt mix and the decoded LtRt 5.1 mix.
The majority of consumers will generally be experiencing the LtRt mix rather than a decoded LtRt, which is only available to listeners that have an AVR or car audio system that supports Pro Logic II decoding as well as a 5.1 surround listening setup.
We recommend using the SurCode for Dolby Pro Logic II decoder as a QC analysis tool. Listen with the decoder to check what the end user with a surround setup will be experiencing while still maintaining the integrity of the more-commonly-listened-to LtRt mix.