Digital cable length- SPDIF vs AES/EBU- 1.5 meter for either?

So why do companies manufacturer very, very expensive 1.0 meter digital cables? Simple, people buy them. I totally agree they should be at least 1.5 meters as I have been involved in comparing different lengths of the same cable on a high resolution system.

I would not be surprised if cable designers do in fact lack knowledge. There’s one well known cable company that sells a digital 110 ohm cable, terminated in RCAs, which is way off base because SPDIF protocol calls for a 75 ohm cable while a 110 ohm cable is an AES/EBU cable and there you use XLRs .

Yes, that could very well reflect lack of knowledge, but another possibility that wouldn't surprise me is that it was done intentionally, to make that cable sound as different as possible than the competition.  My perception has been that it is not uncommon among audiophiles for "different" to be perceived as "better," at least in the short term, even if it isn't.  And as Steve wrote in this paper regarding jitter, which would presumably be the main consequence of this kind of impedance mismatch:

Another interesting thing about audibility of jitter is it's ability to mask other sibilance in a system. Sometimes, when the jitter is reduced in a system, other component sibilance is now obvious and even more objectionable than the original jitter was. Removing the jitter is the right thing to do however, and then replace the objectionable component.  The end result will be much more enjoyable.

Jitter can even be euphonic in nature if it has the right frequency content....  It is fairly easy to become convinced that reducing jitter is not necessarily a positive step, however this is definitely going down the garden path and will ultimately limit your pursuit of audio nirvana.

  Best regards,
-- Al
 

Can someone direct me where I can learn why the 1.5 meter length is important? 

I got a 50 feet AES cable run (using 4 out of 8 channels), it’s freaking perfection, it's the best audio interface by miles until wireless Dante becomes more available.

Pro audio equipment rocks. (Only downside is I’m still selling off my high end audiophile equipments to this day...)