Utility to decode Pro Logic?

[Nermal]

I have a couple of 80s movies here with Dolby Pro Logic audio, but I don't own a PL decoder. It's my understanding that the PL decoder "unfolds" 4.0-channel surround audio from the stereo track somehow.

Is there some software that can take a PL-encoded stereo track as input and then generate the decoded 4-channel audio (such as to an .ac3 file)? I'm having no trouble finding utilities that can go in the other direction, but I'm struggling to find the right search terms for decoding the PL audio again.

Does such a thing exist? Or am I completely misunderstanding how Pro Logic works?

 

[MajorFubar]

Sorry I really need to Favourite this subforum, because audio-related questions like this that I could often at least contribute to just disappear among the bustle of the New Posts list that I tend to browse through once per day.

Back on topic.

I'm not 100% sure how Dolby Pro Logic encoded stereo surround into just two tracks. I've tried Googling it but there's very little technical information out there. More and more I've noticed that articles which I believe should be a good source of technical information about a certain subject are in fact watered-down to attract non-technical casual browsers, therefore increasing the site's chances of people hitting and staying. Sad state of affairs really.

Fundamentally it must be some expansion of of Dolby Surround, and I would urge you to experiment. Dolby Surround overlaid a mono rear-channel as out-of-phase stereo under the stereo channels. Sometimes when sat directly in front of a just stereo TV, you could often sense the 'surround effects' because, for many people (including me). out of phase audio seems to be coming from behind our heads. Therefore it is a piece of cake extracting the 'rear' channel from Dolby Surround soundtracks by inverting the phase of one channel of the audio and extracting just the centre channel.

Give it a go and see what you come up with.

 

[Nermal]

I haven't ignored you, I was just waiting to see whether anyone else replied.

If it's a case of "try this" then without the technical details it's never going to be 100% accurate to how it's supposed to sound. At that point I might as well borrow my parents' decoder and record the output.

This is proving more difficult than I expected. There are a handful of utilities that can convert from discrete surround into Pro Logic, so I'm surprised that there doesn't seem to be anything for going back in the other direction.