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February 2012 Issue - page 2

Article Index
February 2012 Issue
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CABLE CRITIC

I notice that the editor, and the various contributors, are careful to say cables can make a difference rather than an improvement. Of course they make a difference, I have heard it myself, even though I was a strong non-believer. The reason is simple – a cable is a passive device, it cannot amplify anything. But it can attenuate an audio-frequency signal. Thus a cable may, for example, remove the excessive brightness from a system, as some of your reviews have stated. That does not make the cable in any way good, it is simply offsetting one fault with a second fault. The best cable is the cable with the minimum attenuation at all points of the audio spectrum, and the minimum phase change.


A good starting point is to keep the cables as short as possible, obviously. Do not use a one metre cable if a 20 centimetre one will join the items together. Do not use elaborate cables  they are likely to cause phase shifts. Do not use any cable where the return path is of a different construction than the live path, such cables are a logical nonsense. Thus avoid all cables that have any kind of coaxial construction.


One of your contributors, about a year ago, wrote an interesting and thought provoking article that attempted to clarify this minefield. However, he rather spoilt it with graphs showing the high impedance of 75 ohm coax cables at audio frequencies. Of course  they are optimised for use at much higher frequencies. That is why they are called 75 ohm cables!


Getting to the practicalities. My tests have, very much to my surprise, led me to settle on using flat telephone extension cable for all interconnects other than the very low level moving coil to phono amp cable. It gives by far the clearest and most detailed sound I have ever heard, without attenuating the bass. As I have said, as a passive device, it cannot exaggerate anything either. What’s more, it costs 99 pence for 12 metres from my local 99P store! Please do not say Ah, but your system may not be good enough to take advantage of more expensive cables. I am in the happy position of having some very expensive and well regarded equipment in one room and some much cheaper, but still generally highly thought of components in another. The clarity, detail, and good bass of this very cheap cable is blindingly and instantly obvious on both.


Then we have the even more controversial subject of mains supply and mains cables. I have replaced the ring circuit to both systems with direct spurs from the consumer unit to the systems, using heavy duty cooker cable. This has resulted in a noticeable, but not large, improvement. One of my sources is a laptop. To reduce the possibility of losing data due to mains spikes I have used a Masterplug surge protecting extension lead for this, connected to the ring circuit, not the dedicated spur, as my (generally respected) amplifier manufacturer says Voltage dependent resistors and noise suppressors degrade the mains supply and the sound in their instruction books. I am more inclined to believe them, right or wrong, than the snake oil manufacturers. For reasons I do not fully understand, the background noise level, heard as uneven hiss and rumbling noise between tracks, is reduced to inaudibility if the DACs, which are dCS Debussy in one system and Cambridge Dacmagic in the other, are connected to the Masterplug extensions powering the laptop rather than the dedicated spurs. Perhaps because the laptop and DAC becomes a unit?


However, I do have a problem with some of your cable reviews. A recent review of an 875 pound mains cable says that replacing his previous 400 pound mains cable (from the same manufacturer) with this resulted in a major reduction of hardness and mush and removal of the excessive distortion resulted in...etc. Doesn’t say much for the previous 400 pound cable, or his system, does it?


Finally, a question. I have read tests, in your magazine and others, of dedicated network players, music servers and so on, ranging in price from 400 pounds to 12000. What do they actually give me, other than looking nice, that a laptop, a DAC, and a cheap NAS for backup does not?

Mark Powell,

Southampton

 

 

dcs-debussey

The advanced dCS Debussy with it's unique Ring Dac benefits from a clean digital source, provided by a good server.


 

Mark. We get a stream of letters, many in print every month, from readers who change cables and find they do make an appreciable difference and for most it is an improvement. Trying to suggest they are all deluded is difficult to justify. We also hear clear cable differences and better cables do invariably give better results.

Die hard cable sceptics often use your reductionist logic based on the usual simple lumped parameter electrical model for cables, but as I point out repeatedly, this fails to include influences not in the simple model, such as external interference, possible rectification at diodic junctions and what have you. And the fact that we barely understand how power can be transmitted in a field that lies outside the conductor suggests there is perhaps more to cables than the simple passive model you quote. Look at the references quoted by Matt Rowland in our March 2011 issue, p36, which you can also find in the Letters section of our website. They illustrate that this subject has some depth.


I have heard endless demos of cable differences, Chord running an interesting and convincing demo at shows using headphones. A short time ago at one of these demos I listened to three cables, budget, mid-priced and expensive and heard three different presentations, the mid-priced cable being may favourite for specific reasons. Another listener who had just done the same thing agreed with my views when I discussed them with Chord, suggesting there are differences and they are tangible, not illusory.


As an engineer I understand where you are coming from with your view that construction should be physically symmetric, but then you have not taken into account any need for screening so your logic is neither comprehensive nor infallible I’d suggest. Perhaps there are other variables at work too, that none of us understand.  As Donald Rumsfeld famously noted: “there are known unknowns and unknown unknowns”. Mechanisms that influence cable sound quality I believe fall into the latter category.


What expensive, custom server systems give you is a cleaner digital environment, suffering less noise and interference, with improved clocking to reduce jitter. And you get dedicated audio functionality as well. Item Audio expand on this for you below. NK

 

 

aurender-s10

Music servers like the Aurender S10 reviewed in this issue provide cleaner digital than CD players, our tests show.


 

On digital servers, Item Audio say –

CD transports perform variably according to the quality and implementation of their clock, calibre of power supply,  vibration control and handling of EM/RF ‘contaminants’. The net effect manifests in various forms of jitter and rail noise injected into the mains and conductively carried from the transport to the susceptible DAC and amplifier. Swapping a PC for a CD spinner doesn’t change anything at all about the design goals of the transport.


In some ways, a computer transport is inherently better suited to this task: it has a greater processing resource to dedicate to handling the PCM stream. It sidesteps all the difficulties inherent in clanky optical media mechanisms. It offers clock slaving asynchronous transfer options that, at first glance, appear to make the transport irrelevant. It’s file format, sample-rate and bit-depth are agnostic by design.


However, it’s also handicapped by its own sophistication: a computer operating system inevitably squanders a percentage of its processor resource in activity unrelated to audio. It’s smart enough to know many excellent ways to screw things up (hidden filtering, driver interference, volume dithering, etc).

It’s complexity counts against it when we examine the board design: extremely low-rent, mass produced, densely multi-layer components with Byzantine grounding schemes and high-interference switching creating complex noise harmonics right on the board. Furthermore, the primary power supply is usually (by audio standards) a shoddy piece of work that wouldn’t be given house room by an amplifier designer. Much of this noise will inevitably end up where you least want it because of necessarily imperfect isolation.


Although the disc spinner is a headache, electrically-speaking, the 3.5” hard drive is no angel, creating powerful EM fields and sucking up to two amps during playback. In many ways, the simplicity and purpose-designed nature of the CD transport is superior to a standard PC, as many have learned in audition.

It’s easy to see by examining the innards of a Naim, Linn, Yamaha, Bryston or Aurender ‘server’ that it’s not at all straightforward to deliver a truly clean digital signal to a DAC: it requires costly and very well behaved power supplies and extremely tight regulation of the clock’s environment. Taming rail noise and resultant, or independently generated, timing errors and jitter is a non-trivial matter, and is clearly audible and measurable.


It’s interesting to note from the consensus of professional reviews that no matter how expensive or sophisticated the DAC, and how voluble and persuasive are the theoretical promises of the manufacturer, the transport almost always makes its presence felt in audition. Although ‘bits are bits’, everything about the local playback environment will impact on the DAC. Despite buffering and reclocking, in practice, we never entirely escape the maxim 'Garbage In, Garbage Out'.  

Mark Welsh, Item Audio

 

 

 

chord_cable_demo

 

The Chord Co set up an interesting demo at shows, using headphones to hear cable differences.

 

 



 

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