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Topic: Dolby Surround -> How To Check? (Read 2868 times) previous topic - next topic
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Dolby Surround -> How To Check?

This is my first post and I would like to ask whether anyone on this forum knows of a piece of software for PC that checks 2-channel PCM or even MP3 files for Dolby Surround data, just to know whether the file is really encoded in Dolby Surround or not

Dolby Surround -> How To Check?

Reply #1
AFAIK there's no such software & no 2-channel PCM or mp3 contains "surround" info. For instance, Dolby Pro Logic II (5.1) constructs the center, left, right, rear left & right information right from the stereo source. You'll have some troubles though playing mp3 files in PowerDVD 4.0 XP as the decoder is crap.

In regards to mp3 preserving 'surround information' this is more related to preserving stereo image, which can be altered in crappy encoders (Xing's Joint Stereo). The LAME current implementation of Joint Stereo has no such problems.

Also I would try to use the search feature

http://www.hydrogenaudio.org/i...ghlite=surround

edit: typo

Dolby Surround -> How To Check?

Reply #2
of course I know that the surround information is in the stereo sound

all I wanted to know is whether you can check whether such a 2-channel source contains surround information or not

Dolby Surround -> How To Check?

Reply #3
Hi,

You could try and look at the (cross)-correlation of the Left, Right and Surround signals (after decoding). If the audio signal was encoded wtih Dolby, the Surround channel can have information independent of the L and R signals. If the audio was normal stereo, the decoded S signal can only have info from the L and R channel.

Unfortunately, typical surround channel audio is already created from reverberation or delay of L and R channels, so it might not work very good. But for movies it will work quite well.

Dolby Surround -> How To Check?

Reply #4
Quote
Hi,

You could try and look at the (cross)-correlation of the Left, Right and Surround signals (after decoding). If the audio signal was encoded wtih Dolby, the Surround channel can have information independent of the L and R signals. If the audio was normal stereo, the decoded S signal can only have info from the L and R channel.

Unfortunately, typical surround channel audio is already created from reverberation or delay of L and R channels, so it might not work very good. But for movies it will work quite well.


how can I look at the cross correlation?

 

Dolby Surround -> How To Check?

Reply #5
Write some code 

No really, just look for code that computes cross-correlation values for 2 signals, and apply that on the combinations of L and S, R and S, respectively. If you can find code that computes 3rd order cross-cumulants you can apply that directly on the 3 channels.

If you have acces to Matlab, computing and plotting will be even easier..

 
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