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Digital cables shootout test

World tour (digital) sessions

[Italian version]

Reviewer: Lucio Cadeddu
Reviewed: Winter, 2001-2002

Foreword

First of all, by digital cable I will mean an interconnect cable between CD transport (or CD/DVD player used as pure transport) and an external D/A converter (DAC). The DAC can be a completely separate outboard unit or an inboard section of a preamplifier, integrated amp or HT receiver (sic).
There are many ways and standards to connect a digital data source (CD transport, DVD player, DAT etc.) to an outboard DAC: optical (toslink) and electrical (RCA coaxial, BNC, XLR, I2S etc.). For simplicity's sake I'll deal with electrical connection only, using both RCA and BNC connectors (no balanced XLR).
Why? Not because it's the best sounding, just because it is easily available on the vast majority of transports/DACs.

Between RCA and BNC connectors, the first ones are the most popular while the BNC's represent a better sounding choice - for reasons which will be clear in a while.
For various reasons I've decided to test digital cables using both standards: RCA at the DAC's end and BNC at transport's side. The cables I've tested, indeed, are the very same, independently from the connector which has been used. So, perhaps, an RCA-RCA cable sounds worse than the same cable with BNC's at both ends.

As for "price tag" I've decided to keep the range quite large, starting from 70 $/Euro meter till 300 $/Euro meter (connectors included). This will allow me to compare cables into the same price range and then test them against more expensive ones, to see if the extra cash required is really worth the effort.

Two words about the choice of brands. I wanted to keep this test as "international" as possible so I chose cables from almost every "region" of the World, hence we have cables coming from: USA, Europe, Canada and Australia. Some brands are well known and established, others are new kids on the block.
Not every Manufacturer I contacted was so kind to reply. On the other hand, those who replied were happy to send samples for this shootout test.

The test took a lot of time because reviewing digital cables is a tough job and because of the peculiar methodology I applied (see below). Add some personal trouble and you'll understand why this series of articles appears so late. My humblest apologies to the manufactuers involved and to you, loyal and faithful readers.
Now back to the test. Here are the contenders: Audience (USA), JPS (USA), MusicMetre (USA), JC (USA), Gutwire (Canada), Van den Hul (The Netherlands), HiDiamond (Italy), Supra (Sweden), Eichmann (Australia). Every Company, except one (Gutwire), supplied a RCA-BNC cable as requested. Here are brands and models:

The test, for brevity's sake, will be divided into two parts, at least. Prices, tech specs and web addresses will be published into the listening tests articles.
During the tests, other cables have been used, from Tara Labs to Madrigal, including even comparisons with optical connections and a DIY digital cable, the EnjoyTheMusic digital, already tested on TNT-Audio a couple of years ago.

Methodology

Each cable has been "broke in" for 50 hours using several "burn-in" CDs, then it has played standard musical CDs for 50 hours at least.

Each cable has been tested independently into two different systems and rooms. I've asked a friend of mine (Mr. Angelo Ideo) to blind-test the cables: he didn't know price tag of the cables and sometimes not even the brand! Consider also that some of the brands are UNKNOWN here in Italy.
Of course, I've asked him to give each cable a rating, with respect to the most relevant aspects of reproduction (tonal balance, imaging, dynamics etc.). Furthermore, he wasn't aware of my independent findings. At the end of it all, we compared our ratings and discovered how damn close were mine to his. Surprising, considering all the variables involved (and different personal tastes!).
This was not a double-blind test (ABX), it was, IMHO, a far better and more accurate one: two different listeners, using two very different HiFi systems into two very different rooms, rating the products under test without exchanging opinions one with the other. Of course, the two HiFi systems made use of top digital gear from several hi-end brands: Wadia, Vimak and Proceed, to name a few.

Explaination, an attempt

First of all, let me remind you the fundamentals on the S/PDIF digital interface: Physical connection required:

A lot has been said about the sound of cables. Do not even try to mention digital cables to HiFi integralists, they will reply these can't sound different.
Actually, it seems differences do exist. I'll try to give a partial and questionable explaination for this strange phenomenon.
First of all, as seen above, the S/PDIF digital connection standard requires the use of a cable of 75 ohm characteristic impedance: this depends on the square root of L/C, with L being the inductance and C the capacitance of the cable. This means, above all, that standard analog interconnects may not work well as digital cables (impedance mismatch).
Clearly, this can't be the sole parameter to take into account when designing a digital cable. Assuming each cable of the test was of this kind (75 ohm impedance, claimed) something else was making the sound different. For example, I suspect the shielding of the cable matters (many Manufacturers use double or triple shielding) and so the quality of the connectors.
Namely, the closest these remain to the 75 ohm standard, the better. RCA connectors are rarely designed to respect this standard, while BNC's are available both as 75 ohm and 50 ohm versions.
The 75 ohm perfect (and CONSTANT) impedance will avoid the so-called "signal reflections", well known to anyone involved in RF transmissions.
Of the cables under test, only one declared a 75 ohm characteristic impedance ± 1.5 ohm up to 100 Mhz (Supra Trico). The problem is: what happens when the cable is joined to non-75 ohm RCA connectors?

I guess a digital cable can influence the jitter of the digital signal, assuming the 0's and the 1's still transitate flawlessly (actually 0's remain 0's and 1's remain 1's)!.
Another aspect that could be relevant is the propagation velocity of the signal through the cable. This is a physical characteristic of the cable which depends on its electrical parameters. Roughly speaking, it depends on the square root of the inverse of K, the dielectric constant of the insulation of the cable. To name a few examples, PVC insulation has a high dielectricity, hence it causes the velocity propagation to be lower (since it depends on the inverse of K). PE is better than PVC while PTFE/Teflon is better than PE.
This parameter can BE precisely measured in terms of % over the speed of light c. A propagation velocity of 80% c (velocity factor, actually) means the signal transits at 80% of the speed of light (300,000 km/sec). This characteristic varies greatly from one cable to another. For example, PVC allows the signal to travel at 50% of the speed of light, PE at 65.9%, PP at 69%, PTFE (Teflon) at 70% and PE foam at 80%.
The real problem with PVC isn't the delay it adds to the signal. Actually its dielectric constant slightly varies with frequency and hence varies propagation speed. This could be a problem. Some manufacturer claims the dielectric used into his cable is AIR (for increased propagation speed?).

Anyway, the key question is: even if all these aspects were perfectly measurable...how do they relate to audible differences? Good question. Some swear only an ABX double blind test can tell the truth.
I've choosen another kind of methodology (two independent listeners) which isn't affected by the so-called ABX psychological stress. Do not blame me for this, it's a mere attempt to give listening tests an aura of scientific proof.

"Audiophile" digital cables are here mainly because someone asked himself how to trasfer a digital signal from one point to another with the least interference possible. This man is Chris Sommovigo, the first one to manufacture a specially-designed digital cable.
Why not let him explain how the whole thing came out? Mr. Sommovigo, after my request, has written the following interesting article (exclusively for TNT-Audio) that will explain his views on the topic.

© Copyright 2002 Lucio Cadeddu - http://www.tnt-audio.com

Mr. Sommovigo's views

Digital Cables. Those two words when thrown together can spark a raging, vein-popping screaming debate between two otherwise friendly nuns ... not to mention what they do to audiophiles, especially audiophiles enamored of communication over internet news groups. Just point your reader to rec.audio.opinion and pose the question: "Do digital cables make a difference?" and then brace yourself for a brutal battle.
It will usually begin with a touch of eloquence, manners, even rather articulate examinations of the topic. It soon degrades into a lumpy-lipped drooling rage. Why?

It seems that some high-minded and educated individuals believe that the cable connecting a CD transport to a DAC cannot possibly have an effect upon the translation of the digital information that it carries. The argument "bits is bits, and them are bits" usually shows up in one form or another, soon to be followed by a usually incomplete examination of digital theory, error correction, noise shaping, Fletcher-Munson curves, Phase Locked Loops. Wielding this information like a priest might wield a crucifix against a particularly nasty vampire, the denizens of this philosophical camp are usually disappointed when the intended victim of their diatribe doesn't readily disappear in a puff of green smoke. Instead, the scurrilous heathen simply fire back from their "subjectivist" viewpoint that, regardless of what the theory may have to say about the audibility of variations in digital cables, there is an impressively large group of people who have for many years observed and appreciated the audible differences between digital cables.

This is just another layer heaped on top of the whole "audiophile cable" debate that has raged for at least two decades. While Dilbert after Dilbert launches theoretical stone after theoretical stone at the audiophile analog and digital cable world from their own flat-earth, terra-centric universe, the fact remains that over the last 20 years the industry has grown to accept and appreciate the sonic contributions that audiophile cables have made. However, there was a bit of splintering back in the day when digital cables first showed up on the scene some fence-riders accepted the ability of analog cables contributing to the overall sonic presentation of the hi-fi system, but couldn't reconcile that a digital cable could have a similar effect. Their understanding of the digital equation, based largely on incomplete marketing materials, disallowed the digital cable phenomenon. A short-lived victory for the flat-earthers, because the high-end specialized digital cable had quickly become accepted as another important piece of the audio-rig, a component in and of itself.

The initial rise in popularity of separate digital components must be directly credited to Audio Alchemy. Indirectly, one might also credit them with the rise in awareness about the digital cable debate and digital cables in general. The reason is fairly simple: Audio Alchemy was the first to make a truly inexpensive outboard digital to analog converter, the DDE. When the DDE was released it sold like crazy. For the first time regular Joes, audiophiles on a budget, enjoyed the luxury of an outboard DAC and took advantage of that mysterious single RCA jack on the back of their CD players. Thousands upon thousands of DDE's sold around the world to people who suddenly were in need of, you guessed it, digital cables.

Much of the industry initially responded with an unfortunate supply of "digital" cables that were essentially just the analog interconnect cables that they had already been selling, one length broken out of a pair and repackaged for the purpose. The standards for S/PDIF interface (Sony/Philips Digital InterFace) were either largely misunderstood or largely ignored. That's when I jumped in with my first product, the DataStream Reference digital cable. It was a true 75 Ohm semirigid cable, stiff as virgin on prom night, and sported two huge, bulbous connectors that could have been equally at home on the business-end of a hookah. They were shaped that way so that they could extend the 75 Ohm impedance characteristic as far as possible before terminating into the RCA jack on the target DAC. The Illuminati DataStream Reference had the world's very first 75 Ohm RCA plugs. THAT got enough attention from a few of the right people that I was able to actually get the ugly thing listened to. It was actually the first cable to break The $ensible $ound barrier with a fantastic reception by Gerald Burt. A couple of more decent reviews later and the news would be out: digital cables matter, and the proof was the DataStream Reference.

Why did it make a difference? The upshot of the theory was that it provided a correct impedance match for what was essentially an RF interface, and as such allowed for an appropriate bandwidth and didn't allow for as many signal reflections as competitive products did. The important part was that it was probably the first truly proper cable for this relatively new interface, and it was being appreciated.

Over the following couple of years I developed a flexible version of that cable, marketed as the model D-60 and also as the DataFlex Studio. The D-60 was to the digital cable world what the DDE was to the DAC world, and soon the D-60 was the ubiquitous reference digital cable. Good timing, great product, lots of luck and no complaints. The D-60 remains unchanged, still marketed worldwide and still used in both home and professional audio systems.

What made that cable so different from its competition was the attention to the needs of the interface and the standard imposed by the interface. This was my brand of design, my philosophy for getting the most out of the potential of the interface. But it would be short-sighted and unfair of me not to mention that there were plenty of people who didn't prefer the D-60 in their systems and that actually chose cables that did not necessarily adhere to the standards of the interface. While my formula for success was based upon the certain technical requirements of the interface standard, others have enjoyed success with wholly different approaches to the problem. Even today you will find a variety of design approaches in digital cable products, and a variety of adherents to each and every one of them.

As an audiophile and music lover I appreciate the efforts that have been put forth by others in this industry trying to solve the digital cable conundrum. It's at the very least an incredibly interesting subject to participate in and also very satisfying to explore experientially. That is what our beloved editor has embarked upon in this shootout: an exploration of the experience of listening to different digital cables without regard for the technology or philosophy governing their construction just an appreciation for their effect on the music as noted by pure observation.

If repetition and replication can be said to be the mother of scientific method, then observation must necessarily be its father. That is what the babbling, lumpy-lipped flat-earthers fail to appreciate when they scream raging Papisms from the Audio Vatican. Good science is founded upon observation, bad science is trapped on paper. What's it mean? It means that no one can choose a girl or a digital cable for you. Trust your own observations.

Courtesy by © 2002 Chris Sommovigo exclusively for TNT-Audio

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