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Old 22nd January 2005, 06:42 PM   #1
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Default Optical, Coaxial, and RCA

I'm trying to figure out what is a better connection for audio quality over short distances, less than 3 feet, optical or coaxial. From what I have found so far theirs not much difference. I have been making my own rca interconnects with quad-star mic cable and hi-end rca connectors. What is different about a digital coaxial cable and the rca interconnects that I make?

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Matt
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Old 22nd January 2005, 11:39 PM   #2
dangus is offline dangus  Canada
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A perfect S/PDIF RCA interconnect would be made with connectors and cable with the same impedance rating. (75 ohms... IIRC).

However, in the real world it really doesn't seem to matter that much. I use whatever RCA patch cables are long enough to reach from the source to the processor, and the bits find their way from one box to another just fine.

As for which is better... RCA keeps the signal in the electrical domain all the way, while optical links have to turn it from electrical to optical then back again. This may make a measurable difference, but probably not an audible one. Use whatever cable type suits the inputs and outputs you have available.
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Old 23rd January 2005, 03:53 PM   #3
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Thanks
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Old 23rd January 2005, 04:07 PM   #4
nyman is offline nyman  Finland
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The electrical -> optical -> electrical conversation don't change the digital stream. optical cable don't connect the ground of the two devices, this is way you always should choose optical
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Old 23rd January 2005, 04:26 PM   #5
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Quote:
Originally posted by nyman
The electrical -> optical -> electrical conversation don't change the digital stream.
Ever heard of modal dispersion?
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Old 23rd January 2005, 04:29 PM   #6
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I have.........but that is not the point.

If your mic cable doesn't sound better than a TOSLINK, then that just goes to show how bad using a mic cable for SPDIF is.

There are 2 ways to go optical. One is TOSLINK, which is the worst possible interface. Then there is single mode, which is not designed to work with 2 m of fibre.

Yes, it will pass data, but so does TOSLINK. As will twisted pair. Just because it passes data does not mean that it works properly. If passing data is all that you care about, then use whatever you want. If you want it to sound good, then you are going to have to change your way of looking at things.

Jocko
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Old 23rd January 2005, 04:44 PM   #7
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From practical experience at home and at work, coax is the best way to send SPDIF but it seems most pay too much attention to the audio part of Digital Audio and monkey about with transformers.
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Old 23rd January 2005, 05:57 PM   #8
nyman is offline nyman  Finland
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Quote:
Originally posted by rfbrw

Ever heard of modal dispersion?
sure but in a short distance this can't be a problem, the attenuation is a problem though. I agree that electrical transfer is often the one to go for(cheaper), especially in long distances. but TOSLINK do isolate devices from each other electrically. on a 3 feet connection I would definetely choose TOSLINK. There shouldn't be any errors on that short distance, am i right?
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Old 23rd January 2005, 06:33 PM   #9
gmarsh is offline gmarsh  Canada
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No format is strictly "better" than the other, It's all in the implementation.

The goal of a digital interface is to get (1) data from a source device to a destination while preserving all the bits, and (2) a high quality clock to the destination. (1) is easy, (2) ain't.

I'm a supporter of synchronous audio systems and putting the clock in the DAC, which eliminates (2).
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Old 23rd January 2005, 07:10 PM   #10
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At the risk of being stupid, I must say now I'm just confused.

It sound like their is no clear winner, which isn't suprising in the audio industry.

But can someone tell me using facts, what the pro and cons are of each.

And is Toslink just another way of saying optical?
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