Optimum Digital Cable Lenght

I’ve been reading a bit about Coax S/PDIF cables. I’ve read that 1.5m is optimum or short 0.5m . Anyone here have any experiences ? I will add that I’m inclined to go short since my Chord Mscaler and TT2 will be right on top of each other.

Perhaps @Simon-in-Suffolk can help he has experimented with the Chord products?

Naim chose the length of their DC1 cable to be 1.25 metres if that’s any help.


Interesting question… if the cable is a genuine 75 ohm cable its length for all practical purposes should be irrelevant. … that is whole point of using characteristic impedances… ie 75 ohm.
However most hifi 75ohm SPDIF cables are 1.5 metres. The SPDIF 75 ohm coax hardware standard (for domestic products) is specified to 10metres… so that would be your recommended maximum length.
No issue going as short as you need.

BTW balanced AES3 used in commercial setups has a max length of 1km.

1 Like

I would add .02$ worth of comment to this thread.
Maybe not too useful as electrical engineering is NOT MY FORTE!

I am a cable afficondo.
Even digital cables.

Like many things, spending more can equal better.
My suggestion is to forgo length in favour of ‘whatever is the best buy’ available.
As an example, needing a 75ohm cable for COAX duties, my last two purchases have been second hand and/or store clearout.

When my local hifi retailer (about nine years ago), was clearing off Kords Master line cables, albeit RGB cables for TV picture, I bought EVERY - LAST - SET.

I then split them into L/R line level RCAs, and used the remaining ‘single’ cables for Subwoofer duties and even -shock horror- “COAX” digital.

(heck I had gone to the shop to buy speaker cable and they had none, so I even ripped the ends off a few and made some nice main L/R speaker cables…)

The build quality of those cables AND the nature of their plugs termination being TOP TIER actually made them very useful for a range of applications.

When an opportunity came up to buy a CHORD company COAX (digital specific) cable second hand; I took it!
Purpose built for digital is probably a worthwhile moniker for the cable sleeve (/box) and 75ohm is the requirement… but as we know, all sorts of things can contribute to the resistance of the whole part…
I do feel better now I have a Chord COAX cable in place (purpose built) and even some high end Chord Company RCAs (feeding into the Nait XS) inplace… they are ‘nice’ kit.

Don’t be fooled into writing off digital cables as not affecting sound… those zeros and ones DO need to get very precisely down the line, and do so as an analogue signal, and when the eyelets do not match up, it is easy for a zero to become a one/vice versa.
(on head-fi a zealot crew would argue to death about error correction and ‘it doesn’t matter’, but the same people seldom hold matching tiered kit up to very high standards… their expectation bias is that sub $1000 kit is the best there is and are happy using mid tier surround receivers to drive 12" JBLs etc)(they do NOT hear the differences between DACs; says a LOT to me!!)

Sure a correctly built cable is ALL THAT IS NEEDED.
but my two cents is; look for whatever bargain you can get that is at a fraction of its’ full price,… and be willing to gain or lose half a metre in length given the cable will sit stationary behind everything and basically ‘not matter’.
caveat being; sure a longer cable might become an antenna, but I doubt that a COAX (for digital) cable would employ ‘no shielding’ (so as to help analogue the sound)(no kidding I have bought expensive cables that do this!(and handed them on))…

give or take half a metre isn’t an issue, I’d argue… but nabbing a cable worth seven times more money (for peanuts) might just deliver a better signal for those ‘eyelets’ to match up perfectly. (It IS a thing!)

For me, the fixed length of the DC1 was its downfall. With the back of the box a little under a foot from the wall, the cable was pushed hard up against the wall where it sat in a highly visible loop of excess cable. I ordered a cable that was exactly the length I needed for a tenth of the price, and it sounded identical so I eventually sold the DC1.

Indeed, if the source and sink are designed well, the length should be largely irrelevant assuming it’s a properly designed RF 75 ohm cable … I have a range of cables to suit the particular setup I have had over the years including with phono connectors at one end, but using the DC1 cable right now.
Yes there can be sometimes tonal balance differences on connected DACs, but if you like that is down to stray analogue RF loading effects, but that is really DAC/ sink dependent and their sensitivities to these issues, and of course Naim might have optioned their DC1 length for their DAC products in this regard….

Having said that I can still hear subtle differences on my DAVE, but very subtle … and the DC1 plays well, as well as some Gotham 75 ohm cables I have made up for different lengths, but to be honest you only need to pay a few pounds to make up a good properly specified cable with equally specified BNC connectors… that can ‘sound’ wonderful.

1 Like

I tried a Bnc 75 Ohm cable 0,5 meters and 2 meters and much preferred the 2 meter.
Naim DC 1 was vastly better.

Hi Simon. The cables will be factory terminated with Furutech BNC’s . They are going to be used between my Chord TT2 and new Mscaler. The TT2 will sit on top of the Mscaler. I just don’t want 1.5m .of unnecessary cable. From the research I’ve done it’s all about reflections and timing of the signal in the cable. 1.5 is kind of a standard, but very short is also as fine. I’m thinking of Ten inches if the manufacturer can do that.
FYI… USB and Ethernet cables don’t have this reflection issue.

1 Like

Hi sounds good, the degree and effect of reflections will depend on the frequency, length of the conductor and the degree of CI imbalance - this is sometimes measured as SWR. I very much doubt if reflections are going to affect SPDIF which is very tolerant to any great extent.

But yes USB on the data twisted pairs and Ethernet cables can experience reflections as they are impedance terminated and originated, it is a reason why to best use certified ethernet and USB connectors. Higher speed USB are more sensitive to this, and we know some poor Ethernet leads and connectors can suffer with this. Texas Instruments for example make some devices that work to decouple the electronics from the effects of reflections on ethernet connections that would otherwise cause interference within the connect device.

This is why typically when we carry voltages at higher frequencies we aim to use a constant characteristic impedance from source to sink so as to eliminate/reduce reflections at boundaries and therefore losses (and in some extreme high power scenarios - flash overs) … its called Transmission Line theory in electronics…


This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.