Everyone keeps going on about how great the Cardas cables make headphones sound. Is there any truth about cables ever making things sound better in any situation? If you are paying £300$400 and above for a set of headphones, why — apart from on the basis of price — would the makers compromise? That would defeat the objective, right?Via SOS web site
SOS Technical Editor Hugh Robjohns replies: If you really want my advice, I'd say spend your money on something more beneficial to your musical endeavours. I´ve no personal experience of the Cardas cables, but I have extensive experience of after-market cables in a wide range of applications and I remain a skeptic.
At the level of headphone you are talking about (high-end Sennheiser and AKG, for example) I think it fair to say that the manufacturers have fitted what they believe to be entirely adequate cables. I've certainly never felt the need to change the cables on my AKG K702s or Sennheiser HD650s, anyway.
Headphone amps certainly can make a very significant difference to perceived headphone quality, though, and I would say that money spent here is usually worthwhile and easily noticeable. Headphone cables? I don't think so. But I'm sure there'll be plenty of people who have purchased expensive after-market cables and are only too happy to say how they have nothing but praise for them.
My engineering head tells me that if a different cable makes a clear difference then either the (old or new) cable, or the headphone amp, is operating outside of the intended design parameters. If the cable meets specifications for resistance, capacitance, and inductance, then it should work as intended. If it doesn't, then it won't work, and it may affect the performance of the headphone amplifier.
In the SOS September 2011 edition Hugh Robjohns reviewed our Grimm Audio CC1 master clock [find the full review by going to /sos/sep11/articles/grimm-audio-cc1.htm]. He commented that he did not notice an improved sound quality in his system. We would like to point out that the Prism converter used by Hugh Robjohns in his CC1 review has a narrow-bandwidth PLL. As explained at length in www.grimmaudio.com/whitepapers/pll%20and%20clocking.pdf, and more succinctly in www.grimmaudio.com/whitepapers/PLL%20and%20clock%20basics.pdf, the jitter performance of such converters neither degrades nor improves when connected to an external clock.
The listening result Robjohns obtains indeed confirms this and — provided that the internal clock itself has low jitter — this is a highly desirable outcome. Unfortunately, since he sought to comment on the meaningfulness of using external clocking in general, it is important to stress that his observation makes no valid prediction of how converters with wide PLL bandwidths will respond. Popular devices, like the Digidesign 192, have PLL bandwidths of up to 4kHz, and the improvement in jitter performance when slaved to a stable external clock is clearly measurable. Grimm Audio distances itself from companies who claim that external clocking is always good. Instead, with documents like the cited white papers, we hope to clarify when external clocking makes sense and when it does not. Thus informed, users can decide for themselves whether they should specify a low-jitter external clock or whether an ordinary one, or none at all, will do. We believe this is more informative than merely taking a stand for or against external clocking.
Bruno Putzeys, Grimm Audio, Eindhoven, The Netherlands, firstname.lastname@example.org
SOS Technical Editor Hugh Robjohns responds: In fairness, I didn't just test the CC1 with a (loaned) Orpheus; I also used Drawmer A2D2 and Benchmark DAC1 converters, which are my standard bench-test references. These are all well-designed converters that have been engineered from the outset to perform consistently to the highest standards, even when externally clocked, as all professional-grade converters should do.
However, as Bruno says, and as I demonstrated clearly in my article in SOS June 2010 (/sos/jun10/articles/masterclocks.htm), the performance of less well-engineered converters (of which there are, sadly, a great many) can change measurably and audibly when externally clocked. Whether such changes are perceived, subjectively, to be for the better or worse isn't really the point: there shouldn't be any change at all in a properly designed system.
There are, obviously, specific situations where a master clock is wholly appropriate and necessary, and the CC1 is clearly a very good master clock. However, it makes little sense to me to invest in such a device in the hope of changing the performance of a poor converter in some subjectively beneficial, but totally unpredictable, way. I believe the more reliable and professional (and often the more cost-effective) approach is to invest in high-quality converters in the first place — as I have done — in which case external clocking ceases to have any influence on the audible performance.