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jsdspif
Joined: 16 Jan 2016 Posts: 276
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Posted: Fri May 27, 2016 6:35 am Post subject: how does a stereo disc work |
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In a nutshell, so to speak. On say an LP record (or any stereo record) the right and left channel is on the record and the needle picks it up. On CED though I'm thinking maybe that's not the case?? Maybe it's more like an FM radio broadcast where a certain frequency is constantly modulated from a stereo transmitter, the receiver can "hear" that frequency and then does whatever to receive the stereo broadcast ? I'm trying to understand why the toshiba player needs a seperate attatchment for the stereo playback. Or what is being sent to the stereo attatchment. If it is just a right channel left channel thing why didn't they just put rca jacks on the player itself? |
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SelectaVision420
Joined: 25 Mar 2012 Posts: 1424 Location: Hartford
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Posted: Fri May 27, 2016 2:25 pm Post subject: |
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the audio and video on a ced disc via FM carriers.
since the audio and video are broadcast on the same carrier, the audio must be at a lower carrier frequency than video. one channel of audio is placed on a 716kHz carrier freq with a deviation of +-50kHz
i believe the adapter is a modulator that interprets the mono fm signal and breaks it apart into stereo, possibly with a comb filter? i know a couple people who have similar stereo adapters but nobody will open one up to see whats inside.
i also have been looking into making one of my own for my mono sears player. _________________ (2)Sears 274 & 934(80150,10&11350), sft100, sgt250, sjt 090-400, vp550, VDR3000, VP2000 & 4000
complete '84 Dimensia Owner |
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ketonic_dude
Joined: 20 Jul 2012 Posts: 547 Location: Mankato, MN
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ketonic_dude
Joined: 20 Jul 2012 Posts: 547 Location: Mankato, MN
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Posted: Thu Jun 02, 2016 12:17 pm Post subject: |
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On a side note the SGT200 is identical to the SFT100 but the 200 is stereo. If you open up a 200 there is a board added on just off the main top board. This is the board that creates stereo sound. I would think one could unhook said board, build a little box with a power supply and some stereo RCA jacks out the back and put that little board in there and wire it up with a plug for the Wards, or Sears, players with the stereo output jack. But not sure if that would work or not. Just seems like it should. |
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jsdspif
Joined: 16 Jan 2016 Posts: 276
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Posted: Thu Jun 02, 2016 5:26 pm Post subject: |
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I believe the link is for building a stereo generator for transmitting stereo fm signals. I may have one of those if I didn't sell it. I used to operate a FM radio station and at one time was playing around with a different stereo generator besides the one built into my transmitter. The attatchment would be more like a receiver (I think??) it's going to have signals coming into it and then somehow it needs to decipher (???) those signals into a left and right channel. (again this is an "I think" type statement). I suppose the info collected from the disc is going to be the same regardless of player manufacturer, so pulling the board from a 200 and working with it would probably be a good option. (again I really have no idea but it seems correct?). I somewhat don't understand why they went mono with option for stereo being an outboard attatchment? With the high cost of the player to begin with how much more could it cost to just have the stereo board inside to begin with. Having an external module adds quite a bit of cost what with needing an enclosure, cable that connects it to the player etc. If you kind of deduct those expenses vs. just installing it in the player to begin with I wouldn't think it would add very much to the overall cost. |
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kitchensynch
Joined: 24 Feb 2013 Posts: 1087
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Posted: Fri Jun 03, 2016 9:29 am Post subject: |
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FM stereo is fairly simple in concept...
The MONO (L+R) signal on the carrier has an added L-R signal added and the two are used to algebraically extract a L and R stereophonic signal.
The method was approved by the FCC in 1960 by a combination of the GE and Zenith system patents and was inaugurated in 1961. A competing system was called the Crosby system, which used a WIDEBAND DISCRETEE signal instead of the more efficient MULTIPLEX/MATRIXED GE/Zenith system (read less bandwidth, more available room for revenue-inducing things like store music broadcasts, and other nifty things later on such as RDS and add on digital hybrid ("HD Radio") signals on the carrier, although technically HD is a HEADACHE for many older sets with the tertiary sideband signal interference (buzzing sound if your filters aren't up to snuff and can wipe out/really impair weaker stations especially if those alternate channel stations tend to be captured more easily by a sloppy tuner))).
PHEW, get me some oxygen. _________________ A New Vista of RCA Victor COLOR! |
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happycube
Joined: 18 Aug 2014 Posts: 25 Location: United States
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Posted: Fri Jun 03, 2016 10:41 pm Post subject: |
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CED stereo is much more like Laserdisc analog audio than FM stereo - it has a second modulated FM carrier and a CX decoder. With boardcast FM left and right are multiplexed into one signal. |
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Jesse Skeen
Joined: 28 May 2004 Posts: 575 Location: Sacramento, CA
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Posted: Sat Jun 04, 2016 7:40 pm Post subject: |
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Laserdisc audio was always discrete left and right- CED stereo is 'decoded' like FM and analog TV sound. I was a bit disappointed when I got my first player and saw that it worked that way, as I enjoy hearing the noise in stereo on laserdiscs that aren't in the best shape _________________ Videodisc and stereo sound- there's no better value around! |
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kitchensynch
Joined: 24 Feb 2013 Posts: 1087
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Posted: Sat Jun 04, 2016 7:51 pm Post subject: |
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No matter how it's done, the audio on my copy of TRON was really nice, good separation and dynamic range, probably about as good as AFM Hi-FI and probably better than Dolby Stereo.
These days a drive-in might use an FM stereo transmitter for quality sound in some cases. It's better than the FM stereo we had before CDs. _________________ A New Vista of RCA Victor COLOR! |
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happycube
Joined: 18 Aug 2014 Posts: 25 Location: United States
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Posted: Mon Jun 06, 2016 8:12 pm Post subject: |
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Jesse - that got me curious - turns out it's a hybrid of broadcast FM and LD - there are two FM carriers - the 716khz signal is L+R, and the 905khz is L-R. (source: page 15 of the SJT-400 SM, http://manuals.lddb.com/CED_Players/RCA-SJT-400-EN_Service_Manual_Scan.pdf)
Broadcast FM stereo is a more complex subcarrier scheme with a 19khz pilot tone (per wikipedia) |
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kitchensynch
Joined: 24 Feb 2013 Posts: 1087
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Posted: Mon Jun 06, 2016 8:37 pm Post subject: |
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I doubt that it would be thought of as a hybrid as you suggest as laserdiscs and CEDs were developed on a completely different track, but I think stereo sound was an afterthought in BOTH CASES. The early laserdisc audio quality was not all that earthshattering in my opinion as also evidenced by the one-shot DISCO-VISION opening bumper (the V growing in the circle one) that I'd have to look up on that laserdisc site to reference for you although I have it saved). _________________ A New Vista of RCA Victor COLOR! |
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