11 replies to this topic

[Bodyjar]

I am just after some more detailed info on how optical cables work in audio. I've searched here, and nothing, searched 12volt.com and nothing either. Anyone have any diagrams? What happens if the cable is damaged, how will it affect the sound? Are there good and bad types of cables?

Basically any info you can find or give me, I'd much appreciate

Thanks!

[Gordo!]

I thought it was just binary. Light on = 1, light off = 0???

[Bodyjar]

Would like a bit more info than that Matt

[Gordo!]

Too bad!

[pingpong]

If the cables are damaged (like it was split) then the light pulses would refract all over the place, so you would end up with 0 signal I'd believe.

Fibre optic cables do not oxidise and suffer signal interference like copper cables either, so personally I'd doubt there would be much difference in cable, although I could be pulling crap outta my bum (which I am sort of )

[~Spyne~]

fibre optic cables are a group of extremely thin tubes, bunched together to create a thicker cable.
a signal which is sent into a fibre optic cable is split, so that the signal is sent through each tube, where at the end of the cable, all the tiny signals are combined again to create the full strength signal.
if one or several tubes are broken, then the signal is still able to be sent through the cable, though strength of signal/quality will be reduced proportionally to the number of tubes damaged.

howstuffworks.com is a helpful site

[Bodyjar]

Ahhh... so what if the cable was cut somewhere, wouldn't the light entering it destroy the signal?

[~Spyne~]

well if you cut right through the whole cable, yes the whole signal is destroyed and lost.
but if only one or a couple of the tubes inside the cable are cut, then the signal strength and quality are reduced, but not lost

works in a similar way to holographic plates - damage part of the plate, and you can still see the whole hologram, though some of the quality is lost

Edited by ~Spyne~, 04 January 2006 - 05:17 PM.

[pazrs]

When I got my AUSTEL license, they told us that if the sheath of optic fibre (why do people say it backwards) is at all suspect/damaged, to bin it.


Light doesnt bounce around inside, they use total internal refraction.

fuknutz2k, on Jan 4 2006, 03:18 PM, said:

If the cables are damaged (like it was split) then the light pulses would refract all over the place, so you would end up with 0 signal I'd believe.

Fibre optic cables do not oxidise and suffer signal interference like copper cables either, so personally I'd doubt there would be much difference in cable, although I could be pulling crap outta my bum (which I am sort of )

There is a big difference in cable, but its mainly bandwidth related not loss rating related.

[Pulse-R]

Optic fibre, for audio.....
the light (usually red) is modulated with the digitally encoded audio signal by the source unit (CD player, eg.). This format is called S/PDIF or Sony/Philips Digital Interface, and is standard for optical and Co-ax digital audio in consumer equipment. The other digital format is called AES/EBU and is used for pro audio.

the light is shone into the end of a fibre (plastic usually, but some glass ones are around). This is very similar to the old 'UFO' optic fibre lights that change colours, and yes these fibres also work with digital audio... hahaha silly me for trying...
if the fibre is kinked or bruised, it introduces 'scattering' inside the fibre, which causes errors in the digital audio signal (errors like this are called jitter, and can sound terrible in the resulting audio signal) where the same data arrives at some slightly different times due to the scattered beams going a different way through the fibre.

The encoded signal has 3 parts, a bit clock, a left-right clock and a data stream.
because the audio signal in the fibre is encoded with a clock signal, changes in the signal introduced by poor quality or damaged fibre will reduce the receiving device's (usually a DAC) ability to correctly recover the original clock signal.


so the light gets to the receiver, where the pulses of high/low intensity (not on/off) are converted back into electrical signals for the S/PDIF

[Bodyjar]

Ahhh.... thank you very much.