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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