Tell me again: Should I use the Optical or SPDIF interconnect?

[DonH56]

Standard (cheap) RG-6 uses solid polyethylene dielectric and achieves about 0.7c. Better (and more expensive) cables use foamed polyethylene or polystyrene to get those 80%~90% numbers, and use spacers with air as the main dielectric to get 90% and above. I think the best I have ever seen was around 96% but that was a large, very expensive cable with air dielectric (or nitrogen, I forget). Most of the cables in our lab at work are around 80% to 92% for the wideband guys (rated 40~50+ GHz).

None of this matters for analog audio, and digital audio rates (except over HDMI) are generally low enough that it is not a big deal either. For that matter, the biggest latency in the signal path is usually the processing and not the wire (or fiber).

 

[pozz]

Amir has done some testing of this as well: https://www.audiosciencereview.com/...battle-of-s-pdif-vs-usb-which-is-better.1943/

The DAC reviews sometimes show very minor differences between TOSLINK and other connections. The only really broken one I can think of is the Bluesound Node: https://www.audiosciencereview.com/...surements-of-bluesound-node-2i-streamer.6631/

 

[MediumRare]

I prefer to use Toslink over Coax when it's possible, mainly to avoid creating new ground paths through my DAC to the preamplifier.

@amirm have you found any consistent differences in your testing of DACs? I have a DX7 Pro.

 

[GeorgeWalk]

Use copper coax if you don't want to be waiting around all day for the light to propagate through the fiber and the music to start.

Electrical signal via copper - about 300,000,000 m/s.
Light via fiber - about 204,190,477 m/s.

But fiber cables burn in more quickly, thereby improving sound quality faster. Light is hotter than electricity.

 

[VintageFlanker]

But fiber cables burn in more quickly, thereby improving sound quality faster. Light is hotter than electricity.

Don't laugh dude. I'm sure there are audiophiles out there, who believe in burn-in for their optical cables...

 

[GeorgeWalk]

Don't laugh dude. I'm sure there are audiophiles out there, who believe in burn-in for their optical cables...

Maybe they should us SPF 50 or S/PDIF 50 to prevent excessive burn in?

 

[LTig]

RCA allows for higher bitrates. Optical (the plastic light-sewer TOSLINK crap) is limited to 96/24 but sometimes still works with 192/24.

The highest bitrate via Toslink depends on the optical transmitter, receiver and the length of the cable. I know of two pairs of transmitter/receivers made by Toshiba, namely TOTX173/TORX173 and TOTX178/TORX178. The latter is specified for 5m max cable length (30 ns rise time distortion), the former for 10m (20 ns rise time distortion). Although both pairs are specified with 6 MB/s max bitrate it may be that the 173 pair can deliver higher bitrates through short cables.

To avoid or break groundloops from PC's Optical is the way to go.

Yep.

 

[audimus]

Amir has done some testing of this as well: https://www.audiosciencereview.com/...battle-of-s-pdif-vs-usb-which-is-better.1943/

The DAC reviews sometimes show very minor differences between TOSLINK and other connections. The only really broken one I can think of is the Bluesound Node: https://www.audiosciencereview.com/...surements-of-bluesound-node-2i-streamer.6631/

Just to clarify the above, the differences between S/PDIF over optical or coax is not comparable to differences between S/PDIF and non-S/PDIF protocols over any connector because of the differences in the protocols. In particular, the way timing is used.

 

[BDWoody]

But fiber cables burn in more quickly, thereby improving sound quality faster. Light is hotter than electricity.

 

[JIW]

But fiber cables burn in more quickly, thereby improving sound quality faster. Light is hotter than electricity.

Not quite sure what you mean by hotter.

As far as I am aware, none of the photons should be absorbed by the optical fiber so no energy should be transferred to the cable. For the electrical transmission due to the cable's non-zero resistance the current causes heat.

So, contrary to what you say, if heat arising from transmission burns the cables in, the coaxial cable should burn in while the optical shouldn't ever.

 

[pozz]

Just to clarify the above, the differences between S/PDIF over optical or coax is not comparable to differences between S/PDIF and non-S/PDIF protocols over any connector because of the differences in the protocols. In particular, the way timing is used.

I don't understand. The comparison is whether signals show any degredation due to the connection type. The conclusion being, if you have a choice, use USB to ensure data integrity. The contribution of noise or other elements is minor. It goes without saying that the protocols are different.

 

[audimus]

I don't understand. The comparison is whether signals show any degredation due to the connection type. The conclusion being, if you have a choice, use USB to ensure data integrity. The contribution of noise or other elements is minor. It goes without saying that the protocols are different.

It is not signal loss over the wire, it is just copper in both coax and USB cables. It is how they handle typical degradation over wire as part of the protocol.

S/PDIF suffers from jitter related issues as sampling rates go up more than USB. This has to do with the way clock is synchronized between source and what the codec uses.

USB using synchronous mode with source is similar to S/PDIF and using incoming signal to construct the clock but can behave better with a separate clock signal incoming as opposed to extracting from the data as in S/PDIF, so downstream codec will potentially see less jitter in USB than S/PDIF. USB in asynchronous mode requires buffering but can send a clean signal to the codec using an external clock and can synchronize with the source in a feedback channel to affect the rate at which host sends the data. S/PDIF has no such mechanism.

So, in a typical audio stack setup with short runs and low sampling rates like 48khz, there is not much practical difference when both S/PDIF and USB end points are implemented well. But as sampling rates go up or lengths get longer USB will do better.

Was just pointing out that the differences between coax and optical for S/PDIF (the OP) was more due to medium, conductivity, interference, etc and usually a non-issue while the difference between S/PDIF and other type of connectors is more due to nature of protocol used, in particular clock synchronization that can have audible differences at high rates.

 

[Rja4000]

Toslink connector is a crap.
That and the use of plastic fiber and Led transmitter means distance and bandwidth are more limited than RCA + coax (a real shame when you think about it).
Fiber connectors, when not connected, gets dirty if not covered. Both the device side and the cable.
Small cover with spring to close when cable is removed break easily. And caps get lost.
Plastic connector gets rounded when introduce in wrong position. Do that too often, and your fiber cable will not fit right anymore.

For all those reasons, use RCA, with proper connectors.
Use fiber for ADAT or if you have no other choice.

 

[DonH56]

But fiber cables burn in more quickly, thereby improving sound quality faster. Light is hotter than electricity.

Tell it to my arc welder. I got your cable burn-in right here...

 

[North_Sky]

It's fun to read stuff ... optic, cosmic, coax, cosmos, ...

Optical is best for long runs...5 meters plus.
And, coaxial "can" introduce hummingbirds (hum) if not well shielded.
But for short runs (less than 2 meters), get a digital coax cable (100 Ohms) and shielded to be on the safe side. A Composite video cable (yellow RCA connectors - 75 Ohms) would also do.

Me and some other audiophile friends have found that there is more "punch" ... authority, low foundations (bass), satisfying overall music listening flow from a digital coaxial connection over a standard digital optical one, slightly better mids, resolution? It's subtle but with practice you'd swear that you can hear. Or it's all in our imagination?

I've never measured, anyone?

 

[Hayabusa]

Use copper coax if you don't want to be waiting around all day for the light to propagate through the fiber and the music to start.

Electrical signal via copper - about 300,000,000 m/s.
Light via fiber - about 204,190,477 m/s.

Also via coax:

"The speed of light in vacuum is (of course) 2.998 × 108 m/s, which is approximately equal to 1 ft/ns. In coaxial cable, the speed of an electrical signal is about 2/3 of this "

from (here)

 

[North_Sky]

So, just use the fastest cable ...

 

[Zog]

I have found that optical cables are fairly easy to damage.

 

[LTig]

It's fun to read stuff ... optic, cosmic, coax, cosmos, ...

Optical is best for long runs...5 meters plus.
And, coaxial "can" introduce hummingbirds (hum) if not well shielded.

Don't know about the shield, but if both sides of the coax connection have galvanic connection a ground loop may be created. AFAIK the SPDIF standard recommends the use of transformers to prevent such ground loops but it is not enforced and so it seems that nobody implements them anymore. The Arcam Black Box 3 from 1991 had such transformers, and I used them for both inputs and outputs of my DIY digital patch bay because I connected it to the soundcartd of my PC in an adjacent room.

Me and some other audiophile friends have found that there is more "punch" ... authority, low foundations (bass), satisfying overall music listening flow from a digital coaxial connection over a standard digital optical one, slightly better mids, resolution? It's subtle but with practice you'd swear that you can hear. Or it's all in our imagination?

It's imagination. I took once part in a blind test for a group of audiophiles and with each change I could clearly hear the advantages of coax over Toslink (not the others though). Problem was that I still heard the same advantages when the operator did not switch to coax but stayed with Toslink.

That was one of those moments in life where you realize that your hearing sense fools you more than you think.

 

[MediumRare]

Me and some other audiophile friends have found that there is more "punch" ... authority, low foundations (bass), satisfying overall music listening flow from a digital coaxial connection over a standard digital optical one, slightly better mids, resolution? It's subtle but with practice you'd swear that you can hear. Or it's all in our imagination?

I've never measured, anyone?

Hey, can't one of you techie geniuses do a loop-back and measure this quick-smart?