Sound quality from optical out and SPDIF???? - Electronic Circuits Projects Diagrams Free

Electricman2K5 · 1st June 2006, 01:46 PM

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....

http://www.maplin.co.uk/Module.aspx?...oslink&doy=1m6

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 · 1st June 2006, 01:58 PM

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** · 1st June 2006, 02:15 PM

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 · 1st June 2006, 04:33 PM

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 · 1st June 2006, 06:00 PM

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** · 1st June 2006, 07:17 PM

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 · 1st June 2006, 07:37 PM

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** · 1st June 2006, 07:46 PM

Quote:

Originally Posted by 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.

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 · 1st June 2006, 08:08 PM

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!

1st June 2006, 01:46 PM	(permalink)
Electricman2K5 Experienced Member	Sound quality from optical out and SPDIF???? 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.... http://www.maplin.co.uk/Module.aspx?...oslink&doy=1m6 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

1st June 2006, 01:58 PM	(permalink)
Dr.EM Experienced Member	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 __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...

1st June 2006, 02:15 PM	(permalink)
Nigel Goodwin Super Moderator	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. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

1st June 2006, 06:00 PM	(permalink)
justDIY Experienced Member	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"? __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

1st June 2006, 07:17 PM	(permalink)
Nigel Goodwin Super Moderator	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 __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

1st June 2006, 04:33 PM	(permalink)
philba Experienced Member	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.

1st June 2006, 07:37 PM	(permalink)
justDIY Experienced Member	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. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

1st June 2006, 08:08 PM	(permalink)
justDIY Experienced Member	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! __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode