Optical, Coaxial, and RCA

TheDriver41 · 22nd January 2005, 07:42 PM

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?

Thanks,
Matt

dangus · 23rd January 2005, 12:39 AM

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.

TheDriver41 · 23rd January 2005, 04:53 PM

Thanks

nyman · 23rd January 2005, 05:07 PM

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

rfbrw · 23rd January 2005, 05:26 PM

Quote:

Originally posted by nyman
The electrical -> optical -> electrical conversation don't change the digital stream.

Ever heard of modal dispersion?

Jocko Homo · 23rd January 2005, 05:29 PM

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

rfbrw · 23rd January 2005, 05:44 PM

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.

nyman · 23rd January 2005, 06:57 PM

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?

gmarsh · 23rd January 2005, 07:33 PM

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).

TheDriver41 · 23rd January 2005, 08:10 PM

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?

22nd January 2005, 07:42 PM	#1
TheDriver41 diyAudio Member Join Date: Sep 2004 Location: iowa	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? Thanks, Matt

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23rd January 2005, 12:39 AM	#2
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	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.

23rd January 2005, 04:53 PM	#3
TheDriver41 diyAudio Member Join Date: Sep 2004 Location: iowa	Thanks

23rd January 2005, 05:07 PM	#4
nyman diyAudio Member Join Date: Dec 2004 Location: southern finland	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

23rd January 2005, 05:29 PM	#6
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	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

23rd January 2005, 05:44 PM	#7
rfbrw diyAudio Member Join Date: Oct 2001 Location: .	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.

23rd January 2005, 07:33 PM	#9
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	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).

23rd January 2005, 08:10 PM	#10
TheDriver41 diyAudio Member Join Date: Sep 2004 Location: iowa	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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