Selected Playback Problems of Historical Grooved Media

The paper discusses some selected playback problems of the replay and high quality archival transfer of historical grooved media, like cylinders, instantaneous discs and early coarse groove records. The topics outline the problems of noise reduction and the compensation of the horizontal tracking angle by means of stereo playback and modification of the sum and difference signals. A comparison between existing noise reduction methods and analogue as well as digital phase and group delay compensation methods is given and discussed. Finally possible compensation methods for the change in noise spectrum caused by the groove velocity decrease at inner diameters with early discs are outlined. The authors propose a radius equalization in the digital domain by using a digital high pass filter without group delay distortion, using diameter dependent change of cut-off frequency.