Mastering for Records, the methods and problems by Batchelor Tony

Author:Batchelor, Tony [Batchelor, Tony]
Language: eng
Format: epub
Publisher: Snugglebugs eBooks
Published: 2016-07-12T16:00:00+00:00

CHAPTER 4

General Comments on the Playback of Gramophone Records

As mentioned in the last chapter, a pick-up stylus is placed in the groove for playback of gramophone records, and endeavours are made to have the stylus strictly track the amplitudes of the groove, thus providing an accurate reproduction of the recorded signal. On an ordinary stereo record, the maximum amplitudes of the groove will be about 50 micron at the loudest passages and about 50 nm at the quietest ones. In order to track these amplitudes, the stylus must, in the audio frequency range, oscillate at speeds which may peak as high as 30 cm/s and in the extremes, 80 cm/s. This has the effect that, at high frequencies, the stylus is exposed to an acceleration which may be more than 1000 g (10 m/s ). For ordinary stereo records the frequency range is about 20 Hz - 20 kHz (up to 50 kHz for quadraphonic records) . Thus, great demands are made on the capability of the pickup to track the groove, and it must be expected that the groove is elastically deformed during the playback. To this can be added that, owing to its size, the stylus is not able to make the same movement as the cutting sapphire. These tracking errors or tracking distortions are partly conditioned by the geometric proportions.

The various forms of tracking errors and the consequent distortion of the reproduced signal can be described systematically in the following way:

Initially, it is assumed that the hemispherical stylus tip of the pickup, see Figure 3.3., is constantly touching both groove walls, and that no deformation of the groove occurs. Under these circumstances a geometrically conditioned tracking error will occur because of the shape and size of the stylus tip point (i.e. deviation from the cutting sapphire chisel shape). The influence of the tracking error depends on the mode of cutting (vertical/lateral). Also some lateral and vertical tracking angle errors will arise. This is owing to the fact that the pickup stylus and its suspension in the lateral and vertical plane respectively may deviate from the plane at which the cutting stylus moved. The distortion caused by the tracking errors is also dependent on the mode of cutting.

Common to the tracking errors mentioned above is the fact that they are all conditioned by purely geometrical proportions, thereby enabling calculation. Among other things, this is the reason why it is possible partly to correct the distortion during the cutting of the records, if a sufficient amount of variable parameters have been built into the cutting system.

Then, it is assumed that the stylus tip point is steadily in contact with both groove walls, but that an elastic deformation of the groove walls occurs. This deformation depends on the elastic properties of the record material and on the stress, i.e. the degree of modulation, the stylus force etc. The resultant distortion can therefore only be calculated approximately.

Finally, it is assumed that the stylus tip point loses contact with one or both groove walls, or the cone-shaped side of the stylus is in contact with the groove.

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