[78-L] Gradual pitch shifting, was Pitch shifting

[Steven C. Barr]

----- Original Message ----- 
From: "martha" <MLK402 at verizon.net>
> Here's a large and very clear photo of the Controller:
> http://tinyurl.com/ygaww3c
>  But I don't see how a speed or pitch changing program will work, because
> the rate at which the speed changes isn't constant, but rate itself
> gradually changes with each revolution of the record .   You might be best
> off to replace the rubber on the wheel & use the Controller.  (Note the 
> even
> in this pic, the rubber is cracked)
>
Actually, the rate at which the rotational speed (RPM) changes IS 
constant...
it is inversely (I think) proportional to the groove length traversed, in 
order
to keep the linear velocity constant. The first turn of the spiral is 
slightly
less than 10*pi long; the last is around 3.5*pi long. With an ordinary 78,
these lengths are traversed in 1/78 of a minute (c. .7692 seconds), or
40.84 ips, for the outside groove; each following spiral turn 
(proportionately
smaller) must then be traversed in the same amount of time. Since each
spiral is smaller by about .003*pi inches, the linear speed increases
proportionately at that rate.

Steven C. Barr