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Topic: GS1200 and 5.1
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Brad Miller
Administrator
Posts: 525
From: Dallas, TX, USA
Registered: Jun 2003
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posted November 01, 2004 06:47 PM
The term 5.1 means five full range discrete channels of audio, plus a subwoofer (the .1) channel. The term Dolby Stereo or Dolby Surround means 2 discrete channels of audio that is ran through a matrix decoder to derive a center (all sounds mono between the two tracks) that is sent to the center channel, a mono surround channel (all sounds out of phase between the two tracks), and then finally the left is pure left with the identical information/mono part from the right track removed, and vice versa for the right channel. A subwoofer channel can be derived from the original two channels as well. Still, none of this is truly discrete, but as you have noticed can be pretty amazing provided that both channels have truly identical recording characteristics. Therein lies the problem with stereo Super 8mm magnetic tracks. Since there is a physical difference in the tracks, the two will not truly reproduce the source recorded onto them identically. Because of that, there will almost always be dialogue bleeding through the matrix into the surround channels (turn off all speakers except for the surrounds to witness it if you don't already notice it), and general "steering" of the encoded audio will be a little off kilter.
The proper way to re-record a stereo track to preserve the Dolby Stereo encoding as best as possible is to take a strip of the film and record pink noise onto it. Then play that strip back and using a 1/3 octave equalizer and monitoring the output on a real-time analyzer (RTA), adjust the equalizer such that you have a smooth and flat playback response. There you will see how different track 1 and track 2 of Super 8mm mag stripes really are in fidelity. Once you have made the adjustments, you should be able to do a couple of more test recordings through the equalizer such that you end up with a raw playback that is flat. Then you will truly achieve an amazing recording that can accurately be reproduced as if it was coming off of a VHS Hi-Fi tape or a DVD in 2 channel mode.
Adding dbx noise reduction is also a magnificent addition to the process. It will give you almost perfect cd quality playback. I did all of this on a Derann print of Beauty and the Beast and everyone was dumbfounded at the audio quality. They thought for sure I had to be running a VHS Hi-Fi tape alongside the film in sync with it. (A quick switch to 18FPS proved otherwise. )
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