Sound quality from optical out and SPDIF????

[Electricman2K5]

Hi I have a Dolby 5.1 amp (it is 4yrs old) and has optical input only for 5.1(called TOSlink). I want to get a new dvd player it only has coaxial digital 5.1 out.

I want to use the 5.1 amp but it only has optical 5.1 input. At maplin this product is available....

**broken link removed**

It says it converts TOslink optical to SPDIF. My question is will the sound quality suffer??? Also does anyone know which is better quality SPDIF out or a optical output.

Thanks

 

[Dr.EM]

The sound quality can be degraded if the unit resamples the signal. Seeing as it costs £13, I assume it doesn't and is perfectly good. The people here may have experience with that www.avforums.com

 

[Nigel Goodwin]

Coaxial digital and optical digital are exactly the same signals, converters simply convert the 'type' of signal (optic to electric, or electric to optic) without changing the actual data at all.

 

[philba]

yeah Nigel is right. both outputs are digital. to actually do any resampling would take a fair chunk of hardware and a Dolby License. If the signal is getting changed, it will be very apparent - as in total garbage. There are some that claim you get jitter with the digital signal but I can't see much more than a few nanoseconds being added.

true story - I was at a big box electronics store with the fraudulent name of "Best Buy" and over heard a salesman helping a female customer pick out an optical cable. He was pushing the most expensive one ($50, iirc) and said "this is the best. It introduces much less noise than the other ones". I decided to stick my fat nose into it and said "sorry, that's not correct. buy the cheapest - they are all the same." Man did I get a glare from him but I felt good.

 

[justDIY]

hah great story!

if I wanted to run my optical sp/dif signal a few km, maybe i would invest in a "quality" fiber optic cable ... but running it a few feet, just give me a cheap plastic fiber in a pvc jacket ... the protocol is already encoded such that a few ghost reflections and nanosecond delays won't effect it - the folks at dolby did their homework.

there are DSP out there from TI and Voyetra that can receive a sp/dif signal and decode it to discrete channels, and then apply certain changes to the channels, and re-encode it as sp/dif ... but they're well beyond the normal "hobby range" type of chip, and major overkill for a project like this

I'd hazard a guess a transistor, red LED and a pair of AA batteries is all you need to make a "converter"?

 

[Nigel Goodwin]

There have been various projects in magazines over the year, if i recall it's there's very little in them - but you do obviously need the correct optical LED (or photo-transistor) or you can't plug the cable in to it

 

[justDIY]

thats why they sell shrink tubing but I agree, one would need to match up the wavelength of the emitter to the detector inside the amp for things to work in an idea fashion.

I've seen the female toslink connectors with built in emitters for sale in small quanities, so it should be a small matter of some catalog searching.

 

[Nigel Goodwin]

thats why they sell shrink tubing but I agree, one would need to match up the wavelength of the emitter to the detector inside the amp for things to work in an idea fashion.

I've seen the female toslink connectors with built in emitters for sale in small quanities, so it should be a small matter of some catalog searching.

I could probably find some in scrap CD players or stereos?, even some of the really small cheap stereos often have optical outputs - usually to feed to a Minidisc recorder.

 

[justDIY]

yea ... or computer system builders might have some ... recent system boards I've purchased come with a filler plate with coax and toslink connectors on them, prewired to a pigtail even!