High density audio recording disc - has flat based groove with steeply sloped side walls

摘要

The high density audio disc is mechanically scanned with a stylus following the depressions in the base of the disc's groove. The virgin groove (14) is a flat plane area between steeply sloping triangular sides (17,18). The triangular sides are proportioned so that the walls (15,16) sloping down and in to the groove (14) have an apex angle (32) to the vertical (19) between 45 and 30 degrees and definitely less than 60 degrees. The base of the virgin groove (14) is level and the information (13) is mechanically cut into the surface. The groove is scanned, for information retrieval, by a flat based stylus with a base width smaller than the groove width and with a side wall angle to the vertical which slopes out to the groove wall at a smaller angle than that of the groove apex (19). The design improves the signal to noise ratio of the system by minimising groove base imperfection variations and enables a greater packing density, i.e. more than 400 to 500 grooves per mm, to be achieved.