I remember the original threads and article claiming this and had bounced it off a very sharp engineer friend of mine at the time and several others. In short, I don’t believe it is true; there are more than a few high-quality SPDIF and AES cables on the market which test out perfectly at 1.0 meter.As is explained in Steve’s S/PDIF article to which Zavato provided a link, what length will be optimal is dependent on the risetimes and falltimes of the signal provided by the component which drives the cable. (Risetimes and falltimes referring essentially to the amount of time required for the signal to transition between its lower and higher voltage states, and vice versa). Those parameters are rarely if ever indicated in the specifications of digital audio components.
Several other factors are also involved, including the happenstance of how well the impedances of the cable and the two interconnected components match, the propagation velocity of the particular cable, the susceptibility of the particular components to ground loop issues, the jitter susceptibility of the particular DAC, etc.
So there is obviously some unpredictability that is involved. But as someone who has also on occasion been alleged to be a sharp engineer :-) I would consider Steve’s recommendation of 1.5 meters to at the very least provide the best odds of being optimal.
This assumes, btw, that a very short length, such as say 6 inches, is not practicable. In circumstances where it is practicable, I suspect it is likely to be an even better choice than 1.5 meters.
Regards,
-- Al
Edit: This post was written before seeing Kijanki’s post just above, with which of course I agree.