Re: [ARSCLIST] Dynamic pitch correction programs (was: wire recorders)

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 23/07/04, Mike Richter wrote:
> At 10:49 AM 7/23/2004 +0000, Don Cox wrote:
>
>> To correct an off-centre disc, one would need a time-stretch routine
>> with the amount of stretch varying according to a sine wave law. The
>> intensity, phase and frequency of the sine wave would have to be
>> adjustable in real time so that the correction could be set by ear.
>
> Yes and no. Eccentric wow is periodic but also variable in amplitude.
> The amplitude change depends on the pitch of the grooves, so may be
> predictable or may be a function of the music content.

You are thinking of the variable pitch cutting used for LPs? I don't
think that was used for 78s.

But would that affect the off-centre wow? The size of the bumps in a
road is not affected by the slope of a hill.

> The frequency
> of the time variation is exactly one cycle per rotation.

And the rotation time could be fixed by playing all discs at a known
rpm, set by a stroboscope. However, most restorers seem to prefer to try
to match the playing rpm to the recording rpm, as closely as possible.
So unless you know this exactly, you would need to adjust.


> The phase is,
> as Don says, a parameter determined by ear.

Regards
--
Don Cox
doncox@xxxxxxxxxxxxxx