Re: [ARSCLIST] Spoke Pattern

[Graham Newton <gn@xxxxxxxxxxxxxxxxxxxxx>]

This message was sent some days ago and apparently never got to the list due
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Kurt Nauck wrote:

> Does this explain the spoke patterns sometimes seen on 78s? I have always
> wondered what caused this phenomenon. Was it a vibration in the cutting
> machine which caused the stylus to dig a little deeper into the wax?

There are a number of reasons for a "spoke" or moiré pattern to appear on a
disc recording.  Most are due to mechanical problems in the cutting
turntable.  These are often traceable to idler wheels that have become
out-of-round due to wear or leaving the idler engaged for long periods when
the turntable is not running.

Varying large light and dark patterns will be often traced to warped discs,
bad or non-uniform lacquer coatings on the discs, or a warped turntable on
the cutting machine.

Varying small light and dark (herringbone) patterns will be often traced
to heavy hum being recorded on the disc due to defects in the cutting
head driver amplifier or other parts of the audio chain.

Another pattern is "groove bunching" where grouped variations in the spacing
of the grooves is caused by excessive play in the mechanism that carries the
cutting head across the disc surface.




... Graham Newton

--
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