audio-talk

I know very little about the beautiful tiny red laser light that shines from so many digital devices. Will an expensive toslink cable sound better,be better if it is more expensive? I find myself using one from 1990 or so,free with a DAT recorder I almost never used.
Now I'm using one and wonder if such a cable makes a diffeence/improvement.

What,please,does the panel think?

According to a thread elsewhere there are miraculous things being heard when people try glass optical connections.
I suspect that there is a degree of variation in how well the ends of the connection mate up with their respective holes, and this has more to do with the differences being claimed to be heard.

I heard different results at a Hi-Fi show a good few years ago.
The demonstrator was having issues with his rig - the equipment was backing up on the window in the room, and the sun was shining very brightly, and the rig was not behaving itself.
Once it was realised that light shining into the unshuttered optical apertures in the back of the DAC was causing the problems the spare inputs were blocked off with BluTack.
But not before a switch out of optical connectors.
To start with an impressive looking "audiophile" quality was in use.
It was swapped out for a cheap as chips "came with a minidisc" connector, and sound quality improved.

My thoughts are the freebie lead probably weighed a lot less than the beefy audiophile one, and consequently the ends of the connectors mated up tightly in their holes.

I don't think the quality of the fibre is really critical, especially with the length of connections generally used (ie 1 metre), but the blocking out of unwanted background light is.

YMMV.

Spot on Chris, the termination and quality of the end fibre polishing is important. The fibre material glass or PMMA will have little to no affect over 1~5m IMHO, certainly not at the symbol rate of SPDIF with standard rebook material.

BTW it's an LED not a Laser Andrew

I always thought it was laser light ?

Is there not an optimum length for these things, something to do with wavelength ?

I've got one that Andrew I got me, quite long but uber cheap.

It is laser light when you're talking proper communications use.
LEDs don't have sufficient light intensity to light up a fibre optic core that's 20km long. They can't be switched fast enough either.

LEDs are more than man enough for the job when you're talking of the piddling lengths used in the home.

Lasers are a coherent light source where LEDs are incoherent meaning the light waves are not aligned but scattered so the effective 'power' is far less than a Laser and when sent down an optical fibre suffer much higher losses due to the scattered nature / dispersed nature of the light.

Well its a lovely little light! Thanks for your replies. I take it then that optical tos links can stay as cheap as chips. I like that :÷-)

You can have LED lasers tho.

Mike H wrote:You can have LED lasers tho.

Well, strictly speaking you cant, you can have semiconductor laser diodes. Unlike LED's lasers require a optical cavity or resonator of some sort to generate coherent light.

OK that's what I meant.

The main reason for using a LED was because they were CHEAP and the frequencies used by TOSLINK are quite low in terms of digital transmission rates.

When TOSLINK started back in the early 1980s, it ran at about 3Mbit/sec - now they happily run at up to 125Mbit/sec - this is easy due to improved LEDs and better fibre - originally plastics were used, but glass fibres are now so cheap that they are used at a domestic level too - the attenuation they impose is trivial - over 5 or 10 metres, no-one cares

Mostly, within data centres, we use OM3 multimode fibre - this is good for 100metres at 100Gbit/sec, 300metres at 10Gbit/sec or 550metres at 1Gbit/sec. OM4 has a higher modal bandwidth and runs a bit further than OM3, but is much more expensive.

OM3 & OM4 fibres normally have an aquamarine coloured sheath - the older OM1 & OM2 standards are normally orange.

Single mode fibre uses a different propagation mechanism and runs at higher frequencies with low loss - typically, for OS2 you see about 0.4dB/km loss - 80km @ 10Gbit/sec is easy and with signal conditioning and amplification, 1000s of km @ 10Gbit/sec are possible.

FWIW, LEDs can only be modulated to about 620Mbit/sec, so everything in a data centre is laser - also, lasers are a single frequency so the signal all propagates at the same speed through the fibre - because of the data rates we use, you get "blurring" and data errors due to the different speeds of propagation across the spectrum of frequencies even the best LEDs put out...