Currently I am using the stock dCS BNC cables to connect the Rossini DAC and Rossini clock. The distance between the 2 units is less than 20cm and so I am considering to buy shorter branded lengths (30cm ) to keep things a little tidier . I read somewhere that the BNC cables should be a minimum of 1-1.5m for optimal performance but I can’t recall whether this was backed by “science” or just subjective opinion .
Is there a minimum length and do other forum members have any experience of using very short cables to connect the dac / clock ?
Many thanks and a belated Merry Christmas and best wishes for the new year !
Nav
The science is pretty straightforward. Any change from one material to another results in a change of impedance leading to a partial reflection of the signal in a digital ontetconnect. For example at the connectors. The interconnect needs to be of a suitable lenght so that the reflected signal may be attenuated during its travel to a low level. This has resulted in a rule of thumb figure of 1.5m.
I have used both 1.5 m and shorter cables and have preferred the longer lenghts but I would not place a lot of credence on this as exhaustive tests have not been involved. In any case most coaxial cables are reasonably thin and flexible so an extra metre or so is not difficult to hide away.
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As you know I love to live dangerously so I have some irresponsibly short (1m!!) Apogee Wide Eye cables you are welcome to try and see if you like.
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In a properly impedance matched system, the cable length shouldn’t matter.
As long as the amplitude of the reflected signal is small enough, ie, the SNR large enough, then it is of little consequence when summed with the primary propagating signal in terms of the receiver interpreting the signal correctly.
That’s the basis of the push for a longer digital cable, so that the reflected signal can be a little more attenuated when its summed with the main signal, to improve on the SNR.
In practice with dCS systems, I don’t think you’ll find much of a difference, but I think it’s generally a good idea to stick with 1m or 1.5m long cables.
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