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From: Patent Tactics, George Brock-Nannestad

Eugene Hertz started this, and Shiffy responded - I have a small
contribution.

Rumble due to unevenness in the form of local differences in radius gives two
problems - both the low frequency itself from the "bumps" and the frequency
modulation it gives the desired signal - a bump gives a larger radius gives a
faster linear speed, i.e. locally a higher frequency, followed by a lower. It
is a wow effect, and it is difficult to compensate (although digitally,
anything can be done when you lock onto the desired signal and do not get
side-tracked by vibrato in playing, which is in the 3-6 Hz range). The
"ordinary" problem with a bump is that it usually throws the pick-up
cartridge around, and the vertical oscillations may be poorly dampened.
Dependent on where the (short in many cases) tone-arm is hinged, this will
cause a back-and-forth movement of the stylus in the groove that will also
give wow. If the hinge is on the line through the cantilever that problem is
minimized.

I agree with most of what Shiffy said, and in particular

> Another effective technique for dealing with cylinders' tubular eccentricites
> is to run them at 1/2 speed and then double the pitch for playback.

something similar to a blank disk is also a good idea


> Also, it's important to not assume that any given groove is "vertical".  As
> with all mechanical devices, tolerances are involved.  IF a groove induces a
> stylus to meaningfully oscillate at some angle other than true perpendicular
> (+ or - the theoretical standard), then unnecesary low and high frequency
> noises will occur. This is remedied by continually adjusting the phase
> relationship of the stereo cartridge being used to track the grooves.  I call
> the process "vectoring". It's extremely beneficial for ALL monaural grooves.

----- this is where it is extremely important to be precise in terminology,
because we are discussing angles in more than one plane. A stereo pickup with
a cantilever (let us assume it is straight) is sensitive to motions in the
plane perpendicular to the cantilever, and adjusting the contributions from
the two coil sets will enable you to have maximum sensitivity in that plane
in a particular direction - other people call that "matrixing" rather than
"vectoring". We usually say that for hill-and-dale we need maximum
sensitivity in the vertical direction. If the noise contribution is higher in
one of what would be called a groove flank in a lateral groove, then it is
advantageous to decrease sensitivity in that direction. Cylinders played on a
good acoustic machine would not need to transport the soundbox across, only
the cantilever, because the major part of the movement was taken care of by
the spindle. However cheap phonographs had no spindle, and so one side of the
groove tends to become more worn.

However, one real problem is the vertical tracking angle, which means that is
is important that the reproducing stylus performs the same movement as the
recording stylus, and although it is generally in-and-out of the cylinder, it
is not necessarily on a radius. This means that if the cantilever is
tangential to the cylinder, there will be distortion, because it is moving in
the wrong plane. One way to partly compensate for this is to slide the pickup-
cartridge back and forth in the headshell, but unfortunately it is very
difficult to find the precise spot where there is minimum distortion. One can
do it with a test cylinder containing a known signal, but the results cannot
be transferred to an unknown cylinder.

Best regards,


George