Welcome to the wonderful world of 78's.  That's just how it is.  You have
to deal with each record as a thing to itself.
Best,
John Haley
On Nov 26, 2015 6:22 PM, "Andrew Hallifax" <[log in to unmask]>
wrote:

> I'm currently digitizing a series of Odeon 78 rpm discs of recordings made
> in the early 1950s of one particular ensemble and I'm surprised to find
> that
> while most discs render A=c440Hz when replayed at 78rpm (77,92) certain
> exceptional examples deviate by 2% or more. Can anyone suggest a likely
> cause? In some cases, discs ostensibly recorded on the same day whose two
> sides bear consecutive matrices, even differ from each other.
> More puzzling still are a couple of discs where the pitch drops gradually
> by
> around a quarter of a tone (roughly 3%) during playback of the side. If
> anyone can suggest the likely or possible cause of this, I'd be delighted
> to
> read about it.
> Many thanks
>