From: snewman@ccu.umanitoba.ca (S. Newman)
Newsgroups: rec.music.synth
Subject: Re: LP Stereo
Date: 10 Apr 92 06:09:46 GMT
Organization: University of Manitoba, Winnipeg, Canada

In <1992Apr9.105745.19989@cbnewsj.cb.att.com> davet@cbnewsj.cb.att.com (Dave Tutelman) writes:

>In article <RWK.92Apr8212350@taunton.crl.dec.com> rwk@crl.dec.com (Bob Kerns) writes:
>>In article <D88-JWA.92Apr8110325@hemul.nada.kth.se> d88-jwa@hemul.nada.kth.se (Jon W{tte) writes:
>>
>>   From: d88-jwa@hemul.nada.kth.se (Jon W{tte)
>>   Date: 8 Apr 92 10:03:25 GMT
>>   .cs.uiuc.edu> cs318a62@ibmb2.cs.uiuc.edu (Philip M Scopes) writes:
>>      >I don't know if this question is totally appropriate but, 
>>      >Where do you get two tracks on an LP?  Do they really do stereo?
>>
>>   My vote (from disassembling my pickup, and also from knowing the
>>   needle may skip on hard drum beats) is for using both right-left
>>   and up-down orientations.
>>
>>The problem with this is that it's asymetric.  You really want
>>both channels to be handled in the same way.  So take your
>>approach, and simpley rotate it 45 degrees!  Instead of up-down,
>>and left-right, the needle senses up-left/down-right and up-right/down-left.
>>That is, the two independent direction vectors are perpendicular to
>>the groove walls, instead of perpendicular to the groove bottom
>>and parallel to it..
>>
>>      R      L
>>       \    /
>>        \  /
>>         \/
>>         /\
>>        /  \
>>----   /    \  ------
>>    \ L      R/
>>     \       /
>>      \     /
>>       \   /
>>        \ /
>>         V

>Absolutely right!  ...

And about time!!  I can't believe the level of confusion on this
thread -- I mean all us teenagers understood this just fine when
it was invented back in the 50's.  :-) :-) 

Then again I haven't the slightest idea how to hitch a horse to a
wagon (or do you hitch the wagon to the horse?)  Ah well, time
marches on.

>   ....
>One problem, though.  The monaural cartridges had no up-down compliance,
>so the vertical detail on the track got bulldozed away.  This was fine
>if you used the record ONLY on the first phono you played it on.  

Right, but on the album covers (at first anyway) they gave you this
little spiel about how great they would sound on "the stereo OR mono
equipment of your choice" -- they just couldn't bring themselves
to admit that your mono cartridge would destroy the stereo
information.  :-)

>Dave

Back to the groove geometry.  The upper edges of the groove, where
they meet the flat surface of the disk, give you the two channels.
One edge is pure left and the other is pure right.  This was not
intentional it is just a consequence of the geometry.

Someone used this idea to develop an optical cartridge that would
track the two edges of the groove -- instant stereo and no physical
contact with the disk, wow!  I don't think it was ever a success
though.  Scratches or even fingerprints on the surface would have
been a problem and the disk manufacturing process was not likely 
tuned to ensure a clean upper edge on the groove.  Also, the
opto-mechanical technology of the day would have had a hard time
tracking the groove (on a home stereo budget).

-- 
Bill Newman			snewman@ccu.umanitoba.ca
Winnipeg, Manitoba		as236@cleveland.Freenet.Edu