Why do digital cables sound different?

Fair enough, Frogman. Good post. I am mostly a subjectivist, have a lot of money invested in cables and hear a lot of differences between things that many argue must sound the same. I think being open minded works both ways. In this particular case, the idea of family resemblances flies so strongly in the face of common sense (to me, at any rate), that I feel we must temper our observations with an open mind to the possibility that what we observe may be influenced by what we expect to hear.

I just ordered the Mapleshade Double Helix Digital Cable. It is not a coaxial design. Since I have never used a digital cable before I thought that I would start with the unknown. I also enjoy talking with Pierre at Mapleshade who has freely shared some good basic advice on my setup. When my system settles down again I will try some other options from The Cable Company, but for right now there are too many changes going on (in my system) to perform sound auditions. When the time comes I will post to this or a new thread as there is not a lot on this subject at the site right now.

Megasam: yes, all cables have some effect (i.e., error) on the signal waveforms passed though them. However, the beauty of digital communications is that, with proper system design, these analog errors can be ignored or removed at the receiving end. That is, errors are NOT necessarily additive in a chain of digital components, as they are in analog communications (i.e., in analog, the SNR must get worse with each additional component in the signal chain). Example of how errors may be removed in the digital domain include error control coding and reclocking of buffered data. A favorite question of mine is "how can this be so?". When faced with claims of audible differences between digital cables some possible explanations that come to mind are a) placebo effect, b) a substandard cable has been replaced with one of proper bandwidth and impedance (and once it's "right" it can't get "better" in a digital system, or c) some sort of weird equalization of the digital waveform is going where the distortions of a particular cable are being used to compensate for distortions of poorly designed digital data transmitters and receivers in the transport and DAC. In a digital communications system, these kinds of effects are sometimes called ISI, or intersymbol interferance. To me, case c) is not an acceptable state of affairs and cable and audio equipment manufactures should be better serving us.

First - the digital datastream carried on a coax connection is an analogue signal, albeit used to represent 1's and 0's. Second - I have never seen a signal coming out of one of these cables on a scope that is a perfect square wave. Third - lack of perfection in the square wave means jitter. Fourth - jitter produces harmonic distortion in the output of the DAC, different forms of jitter distortion producing different harmonic signatures - some sounding soft, some sounding harsh. Fifth - I have never heard or measured a reclocking device (including the Genesis Digital Lens) that does not reveal some of the jitter distortion created by upstream cables and components. And what is more important is that digital cables do sound different, provided of course you have a high resolution system and sensitive ears. I am intrigued however about the observed phenomena of a cable's sonic signature when used as an analogue interconnect, being present when used as a digital cable. I have heard this too, and with cables other than Kimber, and I reject the placebo argument in the context of how I test components. I find this one harder to explain and can only surmise that we cannot look at interfaces between components as separate systems, and that each interface may leak artifacts of itself into other parts of the total system. The active devices that buffer interfaces are meant to deal with this, but perhaps no real world electronic part works exactly how it is designed to work?

Even with perfect square waves there will be jitter in a clock recovery circuit, due to the stochastic nature of the bit stream. Buffering the data and reclocking with a nice stable clock avoids the jitter problem, at the expense of some relatively long term drift in average sample rates to accomodate changes in the data transmission clock rate. If done properly (i.e., large data buffer, low loop bandwidths), then the time constant would be on the order of seconds. A $49 Discman CD player with "skip free" circuitry does this. So does my Levinson 360S. Now we just have to get audio manufacturers to work on the price points in between. :-)