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optical or coax?


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I'm a bit confused here and would love it if you all could clear this up! I have read various opinions on coax vs optical SPDIF digital output to a DAC. I have read that COAX is better because it does not have to convert the digital to the optical then back to electrical. Transversely I have read that optical is better because it electrically isolates the source from the receiver, thus delivering just the bits. I have also read that cabling is more crucial with optical, and other opinions that COAX digital cable is the weak link. I am currently using wireless with the Transporter. That is very good in my opinion, but I have other components (blu-ray) that I need to bridge. I have a good COAX from Better Cables. Would I be better served using an optical with the 24 bit 96khz output from the blu-ray. Or am I not correct in thinking that I am getting 24/96 from either!

Much appreciated!

 

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Hi Eric:

 

As you have read, there are no clear cut answers to your question. Both coaxial and optical applications have their issues. My own experience indicates:

 

- Transmission distance of optical signals is limited by typical consumer-grade equipment

- Avoid converter plugs on optical cables (e.g. toslink-toslinkmini)

- In the optical world, glass optical cables may be best; good quality plastic may be good enough

- Glass optical cables are delicate

- Optical cables provide isolation that coaxial cables do not, but that may not matter in your system

- Think about the quality of and impact of both optical converters in your signal path

 

More importantly, there are many variables within your own system that no one here can recreate. The only way you will ever know which option works best in your system is to purchase a reasonable optical cable and compare that to your coaxial cable.

 

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Toslink, coaxial, USB

 

There’s a lot to talk about which is better, more musical, dynamics…it’s only an electrical signal with an important difference.

 

Toslink has the advantage of no electrical connection by conduction between the source and the receiver because the medium of data is pulsed light.

 

The light what you see in a Toslink cable is generated by a LED at the source, and at the receiver, a device that receives light and converts the light energy to electrical signals. These devices are called optocouplers and have an inherent long term reliablity problem in that the success or failure of the device depends on how hard the LED is driven, temperature of the device and the switching response of the electrical section.

 

An optocoupler is far from perfect and given current commercial considerations, many devices are at their limit of operation as a normal design criteria. Whether this applies to high end DACs I would hope not, but certainly worth the question for computer sound cards and outputs. This would have a bearing on the throughput by the optocoupler at either end of the cable don’t forget. So you end up with the drama, twice, with degrading optocouplers at different rates since you have different manufacturers of optocouplers. In my line of work in industrial electronics, many optocouplers have failed in service on printed circuit boards after about ten years service. For rotating equipment, you’re lucky to get six years. Current testing for reliability is stated for 1000 hours, so you can get that time at least.

 

So despite isolation advantages, long term, reliable sound quality is best afforded by cabling with copper/silver/ptfe et al instead of the light. It would also explain sound quality differences from built in SPDIF light outputs from sound cards versus using USB or coaxial cables from the same computer.

 

References:

Google : Optocoupler Degradation

 

http://jase.esrgroups.org/2_3_3_08%20proof.pdf

 

http://www.secomtel.com/UpFilesPDF/PDF/Agilent/PDF_DOCS/ISONCONT/01_OPTO/1_636_41.PDF

 

http://vishay.ru/docs/83718/83718.pdf

 

 

 

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