This is topic Dolby Cp-55 non-sync surround channel in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Michael Brown (Member # 890) on 10-16-2001, 07:07 AM:
When we play our CD through the non-sync some of the sound come from the surround channel, But I noticed it is only part of the sound, eg usually the vocals of a song are non-existant in the rear channel or just very quiet. My question is, since cd's are not recorded in dolby stereo, then how is the cp55 creating this effect from the surround channel?------------------
Michael Brown
Bradford Student Cinema
www.Bradfordstudentcinema.co.uk
Posted by Rob Jones (Member # 902) on 10-16-2001, 07:50 AM:
The CP-55 (as well as any analogue surround processor) will, I assume be doing a 2:4 matrix decode on whatever comes into it. As an analogue process, it doesn't 'know' whether the source is surround encoded or not. Even when not mixed that way, you will often get some phase relations in the stereo mix, that when put through the processor will be decoded as surround information.Rob
York Student Cinema secretary (not too far down the road from you!)
Posted by Phil Connolly (Member # 465) on 10-16-2001, 08:14 AM:
Michael,For matrixed surround: Any signal present on the left and right sound track and in phase will be played through the centre channel.
Likewise, any signal on both left and right sound tracks, but in-anti phase (180 degrees) will be played on the surround channel.
The remaining audio information will be played on the respective left or right channel.
You should therefore notice that the vocals of a song, will usually come out of the centre channel because they are usually panned dead centre of a typical stereo mix with no phase shift between the left and right channels.
With a computer, an audio editing package and a Matrix decoder (your cp-55 or a hi-fi pro-logic effort will do) you can experiment with your own surround effects. Eg take a mono wave file, convert it to stereo, phase invert one channel and run it through a Matrix decoder and the sound will mostly come out from the surrounds. With a bit of patience you can create a home made surround mix.
Posted by William T. Parr (Member # 677) on 10-16-2001, 08:28 AM:
Michael,
If you look at the CAT 243 card in the Dolby CP55 there are several sets of Jumpers that will allow for Surround info during NS. On it, the Wake up which has a NS, and a NS2:4 option on it. Also there is a Jumper in the J2 posistion that can be set to allow for surrounds in the NS mode as well. Check these and see if they are set to do so. If they are everything is working as set. If not be concerned since NS is not working as it is set to do.
Posted by Ray Derrick (Member # 1001) on 10-16-2001, 08:53 AM:
All stereo soundtracks have a mono (or sum) component and a stereo (or difference) component. The matrix used in cinema processors uses the sum (L+R) to feed the centre speaker and the difference (L-R) to feed the surrounds.In other words, the surround channel carries the stereo part of the mix and the centre channel carries the mono part, while the left and right channels carry the complete left and right signals respectively.
A normal garden variety stereo soundtrack contains lots of stereo information and this all gets sent to the surrounds. However, because vocals are mostly panned to centre they tend to be mono, so don't make it out to the surrounds, but there is usually some stereo reverb on the vocals so this does get into the surrounds.
The result is that the vocals can often still be heard in the surrounds but they are distant and echo-y because all you are hearing is the reverb.
------------------
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935
Posted by Gordon McLeod (Member # 33) on 10-16-2001, 10:04 AM:
THe CP55 did not actually have a jumper for 4:2:4 nonsynce you have to stuff diodes for that
That feature was introduced in the CP65
The jumper in the cp55 turned on and off a mixed surround signal
Posted by Pete Naples (Member # 761) on 10-16-2001, 01:34 PM:
Gordon, you must get up early! You beat me to replies every time.
Posted by Gordon McLeod (Member # 33) on 10-16-2001, 04:04 PM:
Pete I thought the UK was 5 hours ahead of canada 
Posted by Pete Naples (Member # 761) on 10-16-2001, 04:56 PM:
Here in the united republic of Scotland we set our watches by the opening of pubs, and as you can find a pub open 24 hrs, time is all relative!
Posted by Gordon McLeod (Member # 33) on 10-16-2001, 08:37 PM:
Pubs open 24-7 and with real Tartan on tap I am booking the movers now 
Posted by Bernard Tonks (Member # 809) on 10-17-2001, 06:21 AM:
Strangely enough on my CP55 I lost non-sync completely on the surrounds for the last few days. They’re back again now, but I have absolutely no idea what the problem could have been. The 243 card was removed several times.Glad you’ve got sensible pub hours Pete, England always has to follow Scotland, but we get there in the end.
Posted by Pete Naples (Member # 761) on 10-17-2001, 03:09 PM:
Yo have to move from pub to pub, but you can drink 24 hours. I've never actually managed all 24, got to about 23 on several occasions.!
Posted by Steve Guttag (Member # 268) on 10-19-2001, 07:25 PM:
Please note, on the CP-55...it handles the surrounds differently than one may think.As far as Dolby is concerned, since the CP-55 and onwards the offical "Non-Sync" format (format 60)...Left goes to left, Right goes to right (un-matrixed) and surrounds are derived via the 2:4 decoder.
On the Cat. 243 (logic card) there is a jumper to select the "magic surrounds" for non-sync or to turn them off (inhibit). The jumper jumps in the appropriate diode.
As Gord pointed out...with the CP-65 and the Cat. 443 the ability to decide between a true "2:4" decode (like for videotapes and such) or the standard "Non-Sync" format.
With the Cat. 441 (stereo surround card, needed for digital) one also gets an adjustable "Non-Sync surround" level trim pot to boost the level.
Remember, CDs and other stereo sources are mixed and monitored using a two-speaker system thus Dolby tried to recreate that as accurately as possible with their Non-Sync format with the "magic surrounds" as an option. I suppose this might be changing as now many homes have some sort of Pro-Logic decoding.
Steve
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"Old projectionists never die, they just changeover!"