Quick survey, before @fentonsteve comes along with the physics of signal transfer – and the answer!
All other things being equal: and considering a CD transport with both optical and coaxial outputs, into a decent DAC with both optical and coaxial inputs; and good quality optical and coaxial cables of the same (short) length; which will give the best sound, theoretically (ie, I know you’re supposed to use your ears to decide)?
Thanks.
Please, Sir! I know the answer!
Shut up, Fenton. Give the others a chance.
*tumbleweed*
*dust devils*
Oh, go on then, tell us.
I am tipping optical.
Are you sitting comfortably? Then let me tell you a story.
Back in the early 1990s, I had an Arcam D170 CD transport. It had both coaxial and optical outputs. It also had an optical bit clock input.
The Black Box 5 DAC had two digital inputs: coaxial and optical. It also had an optical bit clock output, driven from a super-stable “oven-baked” 1.4112MHz master crystal oscillator.
With all three links connected up, the CD transport would be slaved to the super-stable bit clock in the DAC, and I could switch between digital and optical data inputs from a front-panel switch. I could also unplug the bit clock link and run the DAC off the CD transport, like everyone else.
The results:
1. Best sound was transport slaved from DAC, using the coaxial data connection.
2. Next best was transport slaved from DAC, using the optical data connection.
3. Second-worst was DAC recovering bit clock from the data, using the coaxial data connection.
4. Worst was DAC recovering bit clock from the data, using the optical data connection.
The optical input reliably sounded “softer”.
Why is this? It can only be the signal bandwidth of the optical transmitter LED/plastic TOSLINK cable / receiver photodiode combo.
The data rate off a CD is 1.4MHz. Most plastic optical cables can just about manage 24/96 off a blu-ray, which is a data rate of 4.6MHz
RG179 cable has a bandwidth of about 3GHz, so 1,000 times that of an optical link.
Recovery of the DAC clock from the bitstream will give a more jittery (soft-edged) clock from an optical cable than from a 75 Ohm coax cable.
What is less obvious is why it still had an effect when the CD transport was slaved from the DAC.
I have a blu-ray player pumping out 24/192 digital audio to my preamp, connected by a glass-fibre optical lead (which has a much higher bandwidth than a plastic TOSLINK one).
You at the back! Are you still awake?
Źzzzzzzzzzzzzzzzzzźzzzzzzzzž
So, (thirty years later!) – is there effectively no audible difference between coax and a modern, glass-fibre optical cable?
I didn’t have a glass-fibre cable at the time, and my blu-ray player only has an optical digital audio output, so I can’t test it.
I went to a lecture by yer man from Chord Electronics (of Mojo DAC fame) and he reckons glass-fibre optical is best, because it cuts out the potential for ground loops.
The coax connections on the Mojo go through on-board opto-isolators.
Thanks, that’s interesting – especially as I use a Chord 2Qute DAC (terrible name, but an excellent DAC).
Mr Spock, activate the on-board opto-isolators! The Klingons are up to their tricks again.
I have done my own, slightly less detailed scientific analysis…
I have a bluray player and a cd player plugged into the same DAC: the former with an optical cable; the latter with coax. If I take the same CD and play it on one and then the other I find it very hard to convince myself there’s any difference worth worrying about.
See below, if both cables are good quality and functioning correctly there isn’t any difference in sound, the DAC quality is what matters
SALVADOR DALI invented the jittery (soft-edged) clock, you know.
No – I think you’ll find that was DONOVAN…
Oh look, the swallows have arrived!
You spelled Dullards wrong, Foxy.
Digital, if both cables are decent quality there will be no difference in sound. If something is wrong you will hear some weird artifacts but the sound won’t change.
Fentonsteve, you have outdone yourself. My answer is who knows but the Chord Mojo is excellent. Hope that helps.
I’d like to thank my agent, and my employer for paying me while I wrote all that.
(…sound of cheering, air black with hats, “c-list” celeb gently leads Fenton offstage…)
For anyone who thinks this isn’t nerdy enough, see here:
https://www.audioholics.com/audio-video-cables/bi-wiring-from-amplifier-to-loudspeaker
I remember trying this years ago – I can’t remember it making a significant difference to the sound quality. Think I tried bi-amping at one point as well – that also fell by the wayside. Must have been a phase (arf!) that I was going through…
I suspect Fentonsteve is having a moment.
I’ve just gone to edit this and there is a grey box with the text “Edith says: If you get any problems just PM @rich…Thanks.” I haven’t noticed that before.
Well, that was one way to spend a tea break.
A hi-fi is a fairly complex electro-mechanical system, and a listening room is a complex acoustic. Most prople would be better off improving their room acoustics before upgrading any equipment.
“Prople”? You weren’t sure whether to type “people” or “proles”, were you? Admit it!
Truth is my typing is all over the place on account of wearing a tubular wrist-support bandage. And why am I wearing that*, you might ask?
Two weeks ago, Mrs F bought a big box of Seed and Feed. First line of the instructions was “Before applying, remove moss and weeds from the grass”. So I got a penknife and removed the dandelions, then got the lawn rake out of the shed and spent an hour each weekday lunchtime, four hours on Saturday and four hours on Sunday, raking moss out of the lawn. The green wheelie bin is full of compacted moss (I had to climb on top of it three times).
It has been years since I last raked the lawn, it has been a very wet and mild winter, and now it looks like brown dirt with a few blades of grass… and yet, still, loads of moss. And my wrist hurts. The sore back and aching arms have eased off, though.
(*) paging Moosey
Most of us find that upgrading room acoustics involves downgrading relationship status.
The path to perfect audio is paved with compromise.
My old boss used to poo poo HiFi spend because he only had ‘ten penny ears’. I pointed out to him that it would cost a shit load more than 10p to make a human ear.
My guess is that the optical cable would make logical sense. But I also suspect that, unless you were really concentrating on the sound (i.e. not listening to the music) you’d be hard pushed to notice.
My brother used to insist that there was no difference in sound quality between his £69 “hifi system” and my considerably more expensive set up, that he’d never heard anything played on, and that I had totally wasted my money. To be fair, I am sure he was just being an arse and trying to start an argument.
HiFi is pretty much the textbook example around diminishing returns (although, to be fair, my Economics lecturer at college used pints of lager on a hot sunny day). I think £69 (especially if he spent it at Curry’s) is way off of the point where diminishing returns start to be a thing.
And I bet his tape player eject was a noisy, violent thing (a slowly damped cassette eject was how we identified quality in HiFi in my early teens. My mate’s Dad’s Nakamechi was sublime in this regard.
Nakamichi slowly damped cassette eject?
(Rubs thighs…)
My Nakamichi Cd2 cassette player got dumped about 10 years ago because nobody wanted it and I hadn’t used it for about 15 years. It was a sad moment.
My brother lost interest in music in about 1979 so I’m not sure why he bought anything.