1 hour ago
While it's a common practice for most major studios to do brand-new 5.1 Surround mixes for the classic catalog titles, sometimes they just repurpose old stems.
If you use this forum Dolby Stereo doesn't need an introduction but if you somehow don't know the TLDR is essentially Dolby Stereo was a technique of getting 4 channels of audio (LCRS) to fit into the usual optical stereo track on a 35mm reel via matrixing (if you want to a longer explanation, check here: https://fanrestore.com/thread-3467.html). Sometimes these mixes would play in discrete "Baby Boom" format in 70mm, hence the 70mm Six-Track part of the thread name. Now in the early days of surround sound on Home Media, many releases would choose to just use their existing Dolby Stereo track and process them back to surround (Much like a theater would've done during the original run). Having an interest in these mixes, I have found a way to identify if a release is using an unfolded Dolby Stereo track.
Software Needed -
Audacity + FFMPEG Plugin
gmkvextractGUI (optional, if extracting from a remuxed source)
For my main example, I'll be using a personal favorite of mine that has two 5.1 tracks on different home media release. Dune (1984).
Below is a screenshot of the surround channels on the 1998 Universal DVD
![[Image: Screenshot-2026-02-19-185413.png]](https://i.ibb.co/60g155JN/Screenshot-2026-02-19-185413.png)
Now you might already be able to tell that the surround channels look to be the same in both channels. This is the first step in identifying as Dolby Stereo only ever used a single mono surround channel. However the second step is the real smoking gun to prove 100% that this is a Dolby Stereo unfold/Six-Track Mix
By right click on the the leftmost side of the track in Audacity, you can change the track view to Spectrogram which reveals...
![[Image: Screenshot-2026-02-19-190229.png]](https://i.ibb.co/PsQ9VXrn/Screenshot-2026-02-19-190229.png)
Matrixing in the surrounds! The spectrogram can easily show the results of the matrix decoding process which makes it HIGHLY likely a track is an unfolded Dolby Stereo track. Now this isn't 100% definitive for one of those 2 reasons.
1. This is age/budget dependant, Some films had discrete mono surrounds while other relied on matrixing, There's also rare case of a film's original mix having stereo surrounds but being released in Dolby Stereo (i.e Indiana Jones, Popeyes).
2. There are rare cases of remixes using matrixed surrounds (again, Indiana Jones) and/or stereoizing the mono surrounds (Blade Runner). So beware of those.
With that being said I hope this is a useful guide for those looking to find 70mm Six-Tracks or Dolby Stereo unfolds on older releases, Cheers!
If you use this forum Dolby Stereo doesn't need an introduction but if you somehow don't know the TLDR is essentially Dolby Stereo was a technique of getting 4 channels of audio (LCRS) to fit into the usual optical stereo track on a 35mm reel via matrixing (if you want to a longer explanation, check here: https://fanrestore.com/thread-3467.html). Sometimes these mixes would play in discrete "Baby Boom" format in 70mm, hence the 70mm Six-Track part of the thread name. Now in the early days of surround sound on Home Media, many releases would choose to just use their existing Dolby Stereo track and process them back to surround (Much like a theater would've done during the original run). Having an interest in these mixes, I have found a way to identify if a release is using an unfolded Dolby Stereo track.
Software Needed -
Audacity + FFMPEG Plugin
gmkvextractGUI (optional, if extracting from a remuxed source)
For my main example, I'll be using a personal favorite of mine that has two 5.1 tracks on different home media release. Dune (1984).
Below is a screenshot of the surround channels on the 1998 Universal DVD
Now you might already be able to tell that the surround channels look to be the same in both channels. This is the first step in identifying as Dolby Stereo only ever used a single mono surround channel. However the second step is the real smoking gun to prove 100% that this is a Dolby Stereo unfold/Six-Track Mix
By right click on the the leftmost side of the track in Audacity, you can change the track view to Spectrogram which reveals...
Matrixing in the surrounds! The spectrogram can easily show the results of the matrix decoding process which makes it HIGHLY likely a track is an unfolded Dolby Stereo track. Now this isn't 100% definitive for one of those 2 reasons.
1. This is age/budget dependant, Some films had discrete mono surrounds while other relied on matrixing, There's also rare case of a film's original mix having stereo surrounds but being released in Dolby Stereo (i.e Indiana Jones, Popeyes).
2. There are rare cases of remixes using matrixed surrounds (again, Indiana Jones) and/or stereoizing the mono surrounds (Blade Runner). So beware of those.
With that being said I hope this is a useful guide for those looking to find 70mm Six-Tracks or Dolby Stereo unfolds on older releases, Cheers!
