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Why do digital cables sound different?

I have been talking to a few e-mail buddies and have a question that isn't being satisfactorily answered this far. So...I'm asking the experts on the forum to pitch in. This has probably been asked before but I can't find any references for it. Can someone explain why one DIGITAL cable (coaxial, BNC, etc.) can sound different than another? There are also similar claims for Toslink. In my mind, we're just trying to move bits from one place to another. Doesn't the digital stream get reconstituted and re-clocked on the receiving end anyway? Please enlighten me and maybe send along some URLs for my edification. Thanks, Dan
danielho
dekay's avatar
dekay
5,721 posts
 
Redkiwi: I get it. It is not only that you say yes and no, but "how" you say it as well. As far as I know nothing is perfect and there are always variences to be had. The sub atomic clock in Denver is pretty accurate, but I would assume that DAC's and digital transmission lines are not even in the same ballpark. Perhaps when we get organic based DAC's all cables will sound the same?
gmkowal5c1a
91 posts
 
Redkiwi, the overshoot and undershoot you speak of is caused by capacitance in the cable. While overshoot and undershoot themselves may not necessarily effect the DAC output signal, the capacitance in the cable may effect the data pulses risetime. This effect, I would assume may be audible. While jitter is a degrading factor in a system of this type the transmission cable is not likely to increase or add jitter to the bitstream. I feel capacitance is the real culprit here. The less capacitance in the cable the better.
gmkowal5c1a
91 posts
 
Ehider, I am still the skeptic, but I appreciate your viewpoint and candor. BTW, Is your employer Burr Brown? Thanks for the reply.
redkiwi
1,092 posts
 
I am not sure we are disagreeing - over and undershoot being a capacitance issue, is the same thing as saying it is a bandwidth issue (but not necessarily the reverse). So far as I know there is no capacitance issue wrt glass cables, but they sound different from one another.
gmkowal5c1a
91 posts
 
I will be honest and say that I do not use fiber optic cables so I can not say definitively there is a sonic difference between digital cables. You have heard differences, so I will take your word for it. As for the reason.... I am an EE not a physisist. If I were to take a stab at it, with my limited knowledge of optics and lightwave, I would guess the differences would be due to propagation delay, loss or refraction differences in the cables. Maybe someone else with a better understanding of optics in this forum could enlighten us both.
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