As I noted previously, the purpose of going digital has to do with prevention of signal corruption. In doing so, we can speak of "bit-perfect" transmission of audio data in a way which is impossible in the analogue realm. For example, if we think about the main "container" of consumer high quality analogue music today - the LP / vinyl - nothing can be considered 'perfect'. Each LP is slightly different in terms of being free from warping or (hopefully) minor groove imperfections from the moment it leaves the pressing plant (even the quality of each stamper used varies by generation and age), each time the LP is played, a little bit of damage happens to it so every playback will be different. Even if you keep it in pristine condition, the ravages of time and environmental factors will take its toll on the material itself in large or small ways. Furthermore, there is no way to replicate the music in 'perfect' form as a result (unless you digitize it of course; but only to the quality of the LP playback gear and ADC).
As we know, the CD technology (~30 years old now!) is different. Small imperfections in the plastic or aluminum 'pits' do not lead to audible anomalies thanks to the Reed-Solomon error correction of the digital data. Furthermore "bit-perfect" ripping is routinely done (obviously to the horror of the music industry over the last few decades) and the result is literally innumerably perfect copies.
Let us turn our attention to "digital cables". For some reason, some people seem to forget the above and believe that different digital cables make a difference to sound even when there is no disagreement that bit-perfect data is being transmitted down the pipe in digital form. In fact, there has never been a plausible explanation provided by the supporters of different digital cables. Some talk of jitter being inherently different between cables, some that perhaps electrical noise will disrupt the phase transitions in a digital signal to worsen this jitter and perhaps degrade the bits. But where is the evidence for such beliefs beyond subjective "impressions"?
An industry has developed around digital cables of all sorts. Some of these cables are extremely expensive with price tags of hundreds to thousands. Purported benefits include more exotic / precious conductors, various types of insulation, winding techniques, upgraded connectors. While this is well and good - nobody denies that a well built USB cable with excellent strain relief and connectors that do not break or oxidize is undesirable - why is it that so often audio quality gets thrown into this mix of features during discussions as if it's some kind of 'given'? If a friend says he/she bought a $150 cable that was well shielded, had great connectors, was the right length, and had great cosmetics, I do not believe I would question the motivations since these are all quite reasonable. But if they said "this $150 cable sounds better than all my less expensive ones", I think it would be reasonable to at least wonder about the truth of such a statement just as much as if the friend said "water tastes better from my wine glass compared to just a regular glass cup". Has there EVER been a proven example of a properly functioning digital cable sounding different from another item of the same type?
When it comes to cabling in general, I find it interesting that talk of sound quality is usually propagated by the audiophile press and audio reviewers on-line rather than directly from the manufacturers (see the addendum below for an example of a cable ad). False advertising is a legal offense after all while reviewers spouting off their opinion is given artistic license as subjective experience. This is all fine I suppose so long as it's "above board", but in a small industry where ad revenue is of major importance in the print magazines and web sites, do we really think there is a significant firewall between the reviewers and the source of financial support? A reminder - cables are one of the highest marked up items for any manufacturer. I wonder just what percentage of a cable manufacturer's budget goes into R&D vs. advertising...
Turning to more "objective" matters, let us recap. Over the last few weeks, I measured a number of digital cables of various types in my standard test setup:
S/PDIF Coaxial cables:
S/PDIF TosLink cables:
HDMI cables (updated November 9, 2013):
In each case, using what I had, I tried to "create" improbable setups (eg. very long cables, use of couplers and extenders) which serious audiophiles would likely feel will deteriorate the signal quality. Yet in NONE of these situations was I able to detect an actual loss of fidelity running test signals which have been successful in detecting various types of anomalies over the course of my postings. Subjective listening likewise did not suggest to me any deterioration in sound quality. In contrast, RCA analogue interconnect measurements can be shown to have subtle differences even with relatively short lengths.
What else is there to say, really? In my opinion, there is no other way to interpret the data than to conclude that digital cables of adequate quality to transmit the data in a bit-perfect fashion makes no difference to sound quality. Furthermore, there is no evidence to suggest that the cables influence jitter to any significantly audible degree (again, "jitter" tends to be the scapegoat for almost all digital imperfections for selling hardware). Yes folks, bits are bits as far as the digital cable is concerned. They were engineered to be like this. Over the years I have tried my hand at listening tests with digital cables; but never once have I been able to convincingly differentiate cable quality in any blind testing.
Of course, I could be wrong and open to this possibility... As usual, if you have good data to show differences between "working" digital cables, please leave a comment.
Enjoy the music...
Here's an interesting advertisement showing "proof" of something (I reproduce this as 'fair use' for the purpose of commentary with no expectation of benefit to myself financial or otherwise):
For the purpose of discussion around just the contents of this ad, I blurred out the company information and trademarked names... You're welcome to check out the ad found on page 45 of the January 2012 issue of The Absolute Sound (same issue as one of the most disinformative series of articles about computer audio ever to 'grace' an audio magazine from "Dr. Charles Zeilig and Jay Clawson").
1. These cables meet or exceed $20K-$60K competitors' performance. What length are these $20K-$60K cables??? What cables cost this much? Are we talking individual cables or cabling a whole studio? All I can say is throwing a huge number out like that could be either "impressive" or absolutely ridiculous.
2. What is this "patent-pending" XXX Technology? Is it metallurgical? Connector +/- plating? Cable topology? Insulation material? Such a mystery! (To be fair, you can read more about it on the web page to some degree and ponder the claims - go see the ad.)
3. "Nice" plots of square waves I guess... So it's "absolute proof" that XXX Technology improve rise and fall times of a square wave. We know nothing of the length, type of wire, or even what changed between the "conventional cable" compared to the "same cable" with XXX Technology. Yeah... Nice and "scientific" looking but totally lacking in transparency!
4. What does that square wave plot mean for audio, exactly? Are they trying to say these are digital cables where more precise square wave transitions might imply less timing inaccuracies? But we see analogue speaker spades and XLR connectors (I suppose could be AES/EBU).
5. Notice there's no claims of sound quality. Even the TAS and Rick Rubin quotes say nothing about sound quality, rather something nebulous like "performance". Interesting, given that TAS reviewers commonly speak of comparative sound quality in their reviews of cables yet the company chose not to include such quotes, why?
6. Notice the nice arrows showing directionality of cabling for the speaker spades... How thoughtful.
Things that make you go... Hmmmmm...