Looking for Advice on Restoring and Scanning Dolby Stereo(A, SR)

[Min young Park]

Hello,

I am working in film sound restoration, I am currently researching methods for scanning Dolby Stereo (A, SR) from the 1990s.

My setup involves:
1. Sondor Resonance to a CP650, Selecting either Dolby A or Dolby SR on the CP650, scan in 4-track or 6-channel, (excluding LFE)
2. I scan the LtRt directly without going through the CP650.

The challenge I often encounter is that channels occasionally get misaligned (e.g., Left scanned as Right), and sometimes the audio quality appears uneven, with dips causing a "bumpy" sound.

After consulting with others, I was advised to try SoundCode, so I purchased the software. However, to use it effectively, I need to use the LtRt, which in my scans has a significant amount of noise since it bypasses the CP650’s noise reduction.

I would appreciate any insights or experiences from those who have worked with Dolby Stereo scanning—how other archives or studios approach this process, particularly regarding noise management and ensuring accurate channel distribution.

Thank you very much for your assistance.

[Phillip Grace]

Hello.

The challenge I often encounter is that channels occasionally get misaligned (e.g., Left scanned as Right), and sometimes the audio quality appears uneven, with dips causing a "bumpy" sound.

The 4 channel analogue output of the CP-650 should be perfectly adequate for re-recording purposes. The problems you describe suggest that the CP-650 itself is faulty, or misaligned. Under normal conditions the channel distribution is 100% accurate. I have had experiences of CP-650 processors occasionally booting up with incorrect channel distribution. A reboot should cure that problem. "Bumpy" sound suggests that the processor requires an "A" Chain alignment. Dolby noise reduction requires accurate signal level at the inputs to the noise reduction cards.

Although the CP-650 should be fine, I would be more likely to choose a completely analogue signal path for the replay and matrix decoding of the stereo optical sound track. That will be the nearest you can get to the original multi-channel mix, and only one A/D conversion will be required in the re-recording process.

Basic system elements are: 1/ One Stereo Optical pre-amp with adjustments for gain and slit-loss equalization. 2/ Two Dolby "A-Type" noise reduction modules. 3/ Two Dolby SR noise reduction modules. 4/ One Dolby matrix decoder. 5/ One LFE (Sub Bass) card, if you want the Sub Bass channel. All these elements can be found in the earlier Dolby processors - say CP-65 or even CP-50, or you could use their studio equivalents in separate modules.
I include, from memory, a sample of Dolby cat numbers for each stage, although there will be others on this forum who will know which other types and revisions perform best.
1/ Cat 108. 2/ Cat 22. 3/ Cat 280T. 4/ Cat 150E. 5/ Cat 160.

When using the main outputs of a conventional cinema processor, set the B chain EQ to flat, and output levels to match your recording system.

[Jesse Crooks]

I would suggest inquiring on the Association for Moving Image Archivists listserv.

[Min young Park]

I would suggest inquiring on the Association for Moving Image Archivists listserv.

Hi, Jesse Crooks, Thank you for the suggestion. I’ll reach out on the Association for Moving Image Archivists listserv.

[Min young Park]

Hello.



The 4 channel analogue output of the CP-650 should be perfectly adequate for re-recording purposes. The problems you describe suggest that the CP-650 itself is faulty, or misaligned. Under normal conditions the channel distribution is 100% accurate. I have had experiences of CP-650 processors occasionally booting up with incorrect channel distribution. A reboot should cure that problem. "Bumpy" sound suggests that the processor requires an "A" Chain alignment. Dolby noise reduction requires accurate signal level at the inputs to the noise reduction cards.

Although the CP-650 should be fine, I would be more likely to choose a completely analogue signal path for the replay and matrix decoding of the stereo optical sound track. That will be the nearest you can get to the original multi-channel mix, and only one A/D conversion will be required in the re-recording process.

Basic system elements are: 1/ One Stereo Optical pre-amp with adjustments for gain and slit-loss equalization. 2/ Two Dolby "A-Type" noise reduction modules. 3/ Two Dolby SR noise reduction modules. 4/ One Dolby matrix decoder. 5/ One LFE (Sub Bass) card, if you want the Sub Bass channel. All these elements can be found in the earlier Dolby processors - say CP-65 or even CP-50, or you could use their studio equivalents in separate modules.
I include, from memory, a sample of Dolby cat numbers for each stage, although there will be others on this forum who will know which other types and revisions perform best.
1/ Cat 108. 2/ Cat 22. 3/ Cat 280T. 4/ Cat 150E. 5/ Cat 160.

When using the main outputs of a conventional cinema processor, set the B chain EQ to flat, and output levels to match your recording system.

Hi, Phillip Grace, Thank you for your response. I'm relieved to know that our approach isn’t entirely off track.
I’ll check the A and B Chain settings as you suggested.

In that case, the setup you recommend involves routing the analog signal(LtRt) through Dolby A or SR noise reduction modules, then through the Dolby matrix decoder for multi-channel recording. This would require each piece of hardware you listed, right?

Thank you very much for clarifying this! The equipment setup is still challenging for me, but I’ll start working through it with the CP650 manual as a guide.

[Phillip Grace]

Hello, Min young Park.

The CP-650 will perform all the necessary functions itself, which is what leads me to believe that your unit is not working properly.
With the processor aligned and in good working order no extra equipment will be required.
The CP-650 processes the optical stereo sound in the digital domain, which requires internal Analogue to Digital conversion, then internal Digital to Analogue conversion to output the sound to the real world. My own preference would be to use a completely analogue signal path to avoid those extra A/D and D/A steps - hence the description of how it was done in the earlier models of cinema processor.

The normal configuration for a cinema processor is to connect the projector optical sound pick-up device directly to the projector input terminals on the back of the processor. The processor then takes care of all of the necessary signal amplification, equalization and processing.

[Mark Gulbrandsen]

I would get a decent dubber and install a reverse scan optical reader on it. Try to find a Panastereo CSP-1200 processor, since it's all analog and still offers the highest quality analog sound reproduction of any processor ever made. I would keep digital processors out of an analog chain.

[Sean McKinnon]

I think what you are looking for is a an optical pre-amp and Dolby Cat. 363 Frame. Just A or SR decoding no matrix decoding or EQ.

[Leo Enticknap]

The activity being described here - playing a Dolby phase matrix-encoded SVA track as if in a projector and then capturing the four output tracks for analog to digital conversion and subsequent recording in digital form - is not, in and of itself, restoration. Agreed that this activity could be done perfectly well using a CP650 in good working order, assuming that the A-chain is properly tuned up (which, from the faults described in the original post, I suspect it isn't). Furthermore, if the CP650 has the AES3 output card (can't remember the cat number), you can also do the A to D in the CP650, too.

However, what is being done is copying the audio tracks, either to reduce wear on the original film element, to provide easier access using modern equipment, or both. Assuming that the original element is in good condition, the A-chain is in good condition, and the CP650 renders the audio in a similar form to which the original 1990s audiences would have heard it, and no remedial work (e.g. editing out pops from splices) is needed, this is not restoration: it is the production of access materials from a preservation master.

[Larry Blake]

Hello Min young Park:

It's important to note—and forgive me for stating the obvious—but you should consider using a stereo optical print for a film restoration only if the 35mm mag master was no longer in existence. Better than that, and definitely the very first choice, is of course the original dialogue, music, and effects "stems," which would most probably be in a four-channel (LCRS) configuration. Using that material not only saves a crucial generation, but gets you where you need to end up today: with separate left/center/right/surround channels.

Please let me know if I can be of assistance to you; I work in film sound and have much experience in restorations.

best,

Larry Blake