8mm Forum: GS1200 and 5.1

This is topic GS1200 and 5.1 in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=000859

Posted by Kevin Faulkner (Member # 6) on October 31, 2004, 06:09 PM:

Just thought I would say that I have done some recording on the GS1200. I was surprised at how good the 5.1 surround sound was when played back through my 5.1 system. The recording quality has gone up in leaps and bounds since finding this cap in the recording circuit which has a bad effect on the recording quality. 5.1 off good stripe is really excellent. [Smile]

Anyone else tried it?

Kev.

Posted by John Clancy (Member # 49) on November 01, 2004, 03:11 AM:

Errm, I think the 5.1 sound is now Dolby Stereo. Had me confused there for a while Kevin - I thought perhaps I'd missed some opportunity.

To record from a DVD has to be from the analogue stereo jacks. However, I often find the resultant surround sound from a good Dolby Stereo source is more pleasing to listen to than the raw tracks of Dolby Digital.

Posted by Maurizio Di Cintio (Member # 144) on November 01, 2004, 08:35 AM:

Hi, Kevin.

I did it once, using a good stereo Hi-fi VHS tape with "Dolby Surround" encoded soundtrack.

When I played back the S/8 recording through the DOlby decoder, the result was good: I mean not astonishing but fairly acceptable: the 4 channels plus the sub, played back what was each once's duty, except for some "crosstalk", probably due to the track2 not comparable quality to track 1.

BTW I used a Eumig 940 to do this.

Posted by Kevin Faulkner (Member # 6) on November 01, 2004, 04:20 PM:

Hi John,
I thought the 5.1 sound was encoded in the stereo signal? and was there if you used the stereo analogue input instead of the optical input of my amp.
The sound is certainly coming through all 6 speakers and the THX logo effect moves round all 5 speakers when playing the recording back on the GS. Ok the signal to noise is not as good but it is certainly very good for 8mm. Now I wish I had a set up like yours [Wink]

Kev

Posted by Brad Miller (Member # 2) on 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. [Smile]

)

Posted by Maurizio Di Cintio (Member # 144) on November 02, 2004, 03:22 AM:

Great info, Brad!

I've got a question: is it possible, effective-wise, to replace pink noise with the noise you pick up with a stereo tuner in-between radio stations?

Cheers

Posted by Brad Miller (Member # 2) on November 02, 2004, 03:29 AM:

Nope, that's not true pink noise. In the simplest of terms, pink noise is every frequency in the spectrum being heard at the exact same volume intensity. FM white noise would not give you a flat response if you were to look at it on a RTA.

Posted by John Clancy (Member # 49) on November 02, 2004, 07:37 AM:

It's probably worth adding that every projector plays back a Super 8 recording differently. Even two apparently identical GS-1200's will reproduce variations on any Dolby Stereo four channel separations.

The only way I've come across to achieve consistent Dolby is to play the film back on the machine it's been recorded on. Otherwise it's really just a stereo recording with varying degrees of leakage over the channels.

Posted by Brad Miller (Member # 2) on November 02, 2004, 12:15 PM:

Yes, very true. However the leaders should have pink noise recorded onto them during the re-recording. This is how 70mm mag is handled. From that point a loop can be made out of the excess leader down the road for proper equalizing and/or head alignment when playing back on different equipment.

UBB.classic^TM 6.3.1.2