Digital losses?

[brainz2000]

Looking for a piece of advice .....

My Beresford DAC is a good 4m from the DVD player I want to feed it occasionally.

If I run a coaxial digital out to the DAC, circa 5m once it has gone around the room, will I be losing much sound quality ?

If this is not recommended, then is the optical interface a better option?
(Can I get 5m of SPDIF optical cable?)

I am also hoping to feed a digital signal from a PC on the other side of the room.

I was planning to put a USB sound card near the DAC, and use a 5m USB to move the signal in the digital domain to the soundcard, thus minimising the signal path between the sound card and the DAC. Is this likely to be better than keeping the soundcard near the PC and then using long SPDIF to move the signal to the DAC?

Any guidance would be gratefully received ...

tim

[DSJR]

Am I right in suggesting a very low loss UHF co-ax cable at the very least?

There are wires out there (Ecoflex 10 and the air-gapped 7mm one they sell) that are measured in losses per Km at RF frequencies, so a few metres *shouldn't* cause any attenuation.

The most important thing is for the cable to retain a "clean" waveform to the DAC I think.

[Themis]

If you need a long digital cable, I would suggest a 6meter 75ohm coax cable.

(there's even a theory saying that coax of 6m are better than the ones of 1m... go figure)

[brainz2000]

Dave

Was thinking of purchasing a custom made Van Damme cable designed for the purpose ....something like

http://cgi.ebay.co.uk/5m-Neutrik-Van...d=p3286.c0.m14

It isn't going to break the bank, but should be reasonably well made and uses the right materials I think ...

To date, I've used a short digital interconnects sold by Stan - but nothing 5m long ....

Lots of people seem to say that you can "hear" different co-ax cables, although I've none that I can compare in A/B mode so I cannot validate this ... just wondered if I'm about to downgrade the sound or whether it is not likely to make much difference ...

Is this the kind of thing you were suggesting ....

Thanks for the input

tim

[Themis]

Lots of people seem to say that you can "hear" different co-ax cables, although I've none that I can compare in A/B mode so I cannot validate this ... just wondered if I'm about to downgrade the sound or whether it is not likely to make much difference ...

Hi tim,

well, strangely enough, the better the equipment design (of player and dac) the less it benefits of "perfect" coax cables.

[MartinT]

If you need a long digital cable, I would suggest a 6meter 75ohm coax cable

Seconded, and make sure it is properly 75ohm cable. It will perform much better than 6m of optical as the jitter levels will be a lot lower (light bouncing around the side-walls of optical cable create smear in the waveform rather than nice sharp edges).

[Labarum]

Dave

Was thinking of purchasing a custom made Van Damme cable designed for the purpose ....something like

http://cgi.ebay.co.uk/5m-Neutrik-Van...d=p3286.c0.m14
tim

Anyone tried the analogue cables?

http://stores.shop.ebay.co.uk/Pro-Au...Q_fsubZ6767566

Good prices. QED cables start around £20.

[Chippy_boy]

Seconded, and make sure it is properly 75ohm cable. It will perform much better than 6m of optical as the jitter levels will be a lot lower (light bouncing around the side-walls of optical cable create smear in the waveform rather than nice sharp edges).

Because of friction presumably. Light rubbing against things etc.

What a load of tosh.

The (alleged) higher jitter in an optical connection is due to the electical>optical and then optical>electrical converion going on at both ends, not what happens in between. For long runs you are actually better off with an optical interconnect! A good toslink cable is good for 100ft or more.

[MartinT]

Because of friction presumably. Light rubbing against things etc.

What a load of tosh

Err no, it's because different packets of light take different paths as they travel along the fibre. Plastic fibre (which is used in most Toslink cables) is worse than glass in this respect. It's a well-known phenomenon. But what do I know, I'm only an electronics engineer who took opto-electronics as a degree module all those years ago.

[Chippy_boy]

Err no, it's because different packets of light take different paths as they travel along the fibre. Plastic fibre (which is used in most Toslink cables) is worse than glass in this respect. It's a well-known phenomenon. But what do I know, I'm only an electronics engineer who took opto-electronics as a degree module all those years ago.

Sorry for the delay in replying.

Your quals have perhaps clouded your common sense.

Different packets of light don't take different paths. How on earth could they. Is the emitter to send some of them out sideways? Yes, it is true that each and every packet will go through many internal reflections along the fibre and I can also accept that this will lead to a smearing of the signal and a narrowing of an eye diagram. But that smearing will apply to each and every packet equally.

i.e. the temporal smearing of the data stream will not introduce bit-to-bit timing errors (i.e. jitter) because any time smearing is consistent across data packets. The fibre would have to be vibrating wildly in order to introduce randomness into the path of each packet for that to be the case.

As I said above, most of the jitter is caused by the electro-optical conversion and vice-vera, not by the cable.