A theoretical and experimental investigation into the causes and mechanism of playback surface and groove noise of recorded media has been made. It is shown that such noise can be considered as arising from the random superposition of voltage pulses produced by local changes in the number and size distribution of welded friction junctions or asperities supporting the playback stylus load. A generalized noise equation, involving the physical parameters of the recorded medium and the playback stylus, has been derived and shows reasonable agreement with the measured playback noise spectra for several cold‐flowing and rigid plastic surfaces. From the noise equation emerges a concept of modulation noise and prediction of its dependence on modulation velocity. Examination of the playback noise level as a function of recording and playback conditions has also been included. It is also shown that surface noise measurements can be used to give information concerning the n/a ratio associated with the theory of friction.
The measured lower limit of wide band playback noise for most plastic surfaces corresponds to an equivalent rms lateral noise velocity of 10−2 cm/sec or equivalent lateral noise amplitude of 1 microinch peak at a linear velocity of 15 cm/sec. The equivalent roughness is thus half of that associated with an optical flat. Using this information, it is shown that at 1000 lines/in. information density a signal/noise ratio of 50 db at a linear velocity of 15 cm/sec should be realized.
