Analog Dolby Surround -> digital possible?

[IvanP]

I'd like to copy my own original VHS tape to DVD preserving maximum audio/video quality. It's 114min performance of 'Lords of the dance' in Hyde park London from 1998. It was not released on DVD and I'm afraid of damaging the tape in future.
Picture is 16:9 but unfortunatelly not real one but letterboxed and an audio is analog Dobly Surround.

I'd like to capture using HuffYUV @ full PAL resolution and audio in stereo@48kHz. I hope that 4 surroud channels L, R, Center & surround (mono) will be still "someway" preserved in sampled stereo audio.

My question is.: Is it possible to extract those four separate audio channels and encode it to digital surround that can be muxed with MPEG2 video later? What software to use for processing audio? Does anybody know?

thanks

Ivan

[Chuckwagon]

The short answer would be no. Oh, I'm sure you could spend a good deal of time implementing a way to capture the signal being sent to each speaker and then building a 4 track audio for your new digital, but it wouldn't be worth the time. Analog Dolby Pro Logic, which is what I assume your tape is using, isn't really 4 channels. It is stereo, L+R, that is recorded in such a way that when it is run through a decoder the signal can be seperated out to the appropriate channels. So all you really need to do is insure you get a good quality capture of the stereo signal on your tape and you can simply use that on your digital copy in the future. The fact that the signal comes off digital won't matter, as long as the original stereo is reasonably intact you should still get the same Dolby Pro you had before. Many DVDs currently have a stereo track in addition to the 5.1 track. Both are digital, and the stereo track when fed to a Pro Logic decoder works fine. So you should have no problem.

Chuck

[Indiana]

Yes, retaining the DolbySurround sound is no problem, since it's encoded into the normal stereo signal (as chuckwagon said). And it's quite robust, it even "survives" mp3 encoding. I'm capturing from my VHS tapes and from TV to HuffYUY or MJPEG and stereo sound and transcode the capture to DivX4/mp3 later on. The DolbySurround is preserved with this procedure at least at any decent mp3 bitrate (>112KHz)

[Chuckwagon]

While you may get good results using compressed audio (MP3, etc.) it would be safer to maintain as much of the original signal as possible. The Pro Logic system uses differences and samenesses (Is that even a word) in the left and right channel of your stereo signal to extract the center and surround channels. Since compressors may alter these channels they can alter the way the signal is encoded. There is an excellent white paper describibg the Pro Logic process here at this link:

http://www.dolby.com/tech/whtppr.html

So to be safe I'd try for the highest bit rate I could get so that changes to the signal are minimized. Although I'm sure most people wouldn't notice anyway, so long as some noise comes out the surround and the dialog stay centered more or less.

Chuck

[IvanP]

Thanks to both of you.

Ivan