Optimal digital cable length -- science or voodoo?

1.5m might be optimal for particular slew rate of the output driver but it is different from transport to transport. Some drivers keep constant dv/dt (slew rate control) while other don't. Calculation of the reflections effect on the signal shape is pretty difficult since output of the driver is nonlinear. Long time ago people used Bergeron diagrams to evaluate reflections in transmission lines but it isn't simple.

If you hear difference between 1m and 1.5m cables then modding (or at least evaluating) output driver on the transport is probably beneficial.

Kijanki - I used to mod lots of transports, all kinds, to improve the rise-time of the output driver. It usually allowed the customers to use a 1m cable rather than the 1.5m, saving them some money. Of course the mods cost money too. I dont mod ttansports anymore since I am a firm believer that computer audio is not only the future, but can easily outperfrom the best transport on the market at a fraction of the cost.

Steve N.
Empirical Audio

Pure voodoo. Talk with some of the principles at any of the reputable mfgrs. The answer will be the same. Get the length you need and the best quality you can afford. Cable length just is not an issue at the frequencies being transfered.

Steve - I feel the same. 500GB external Firewire drive costs about $100 and can store around 1000 CDs. Second external drive can be used as a backup kept in different house. In addition other formats with more bits and higher sampling rate can be supported. All this and convienience.