Even high-end equipment for the highest of demands is powerless against light scatter in CDs. Laser beams are reflected numerous times and stray this way and that over the CD's surfaces. This audibly affects the reproduction. The sound loses its clarity and transparency. The beam diffusion cannot be avoided by error correction.
Does green or black work?
A hot tip in audio expert circles is the colouring of the CD's edge with a felt pen, to absorb the light scatter. The effect unfortunately doesn't deliver on its promise. Green as a complimentary colour to the red laser should bring better results, this is however often not the case as many lasers work with the infra-red spectrum.
Simple and effective: the 36° bevel
Turning round and absorption
In exhaustive tests biochemist Dr. Erich Schrott and engineer Wolfgang Schneider have looked for ways to eliminate the disruptive reflections. They found an amazingly simple, yet highly effective, tuning method. The CD's outer edge is bevelled and works as a trap for the light scatter. Black colouring absorbs additional misrouted laser light. An edge angle of 36° brings audibly the best results.