There is alot of contradictory info about this question, but as best I can gather it is for toslink cables that many people experience gains with 1.5 or 2meter cables. They claim that this has to do with stabilizing the early reflections of the lightpulses in the tube. For a regular electical signal like s/PDIF I have never heard a reasonable argument that longer cables can do anything but hurt. However, the standard was designed to accomodate cables up to 2 meters in length with no significant alteration of the signal. That said I use a 0.5m Illuminati D-60 and am very happy.
