[78-L] constant velocity records, was Value of 78's

[Michael Biel]

David Lennick wrote:
> I'd forgotten about constant velocity discs used during wartime..mentioned here.
> http://www.lostmag.com/issue3/memory.php
>
> dl
>
>   

Those are the Memovox discs and are 16-inch not 18-inch and are 
celluloid, not glass.  They later made them of clear vinyl and those 
don't crack like the celluloids do.  The writer got his facts about 
different formats all mixed up.  Another constant velocity system of 
that era was the Gray Autograph dictating machine which used blue vinyl 
discs that had serrations around the half-inch spindle hole to grip the 
spindle.  The turntable was unmotorized and there was a little motor 
with a rubber wheel at the recording/reproducing head which drove the 
turntable.  Naturally the rotational speed changed as the diameter 
location of the head and wheel changed.



> Graeme Jaye wrote:
>   
>>  With normal CAV discs, the linear speed of the groove
>> gets slower towards the centre of the disc, this results in a poorer
>> frequency response.
>>
>>     


Ironically, in LaserDiscs the CAV are the HIGHER quality discs.  They 
enable freeze-frame because each disc rotation is one video frame, and 
to get freeze frame all you have to do is stop moving the laser 
mechanism.  CLV discs require a memory in the machine to freeze frame.  
They start at the center with the same rotational speed as the CAV but 
then, like CDs, slow down as the laser goes outward because the speed 
was set at the optimum necessary speed already at the center.

Mike Biel  mbiel at mbiel.com