Optical versus Coax

[HDTV Forum]

I'm not an expert on toslink, but usually jitter is anticipated for in a comm channel and the data is resampled with a clock on the receiver end. Therefore several nanoseconds of jitter are not seen because the data is resampled when the data is known valid. Here's something I found at http://www.epanorama.net/documents/audio/spdif.html :

The AES/EBU standard for serial digital audio uses typically 163 ns clock rate and allows up to +-20 ns of jitter in the signal. This peaks to peak value of 40 ns is aroun 1/4 of the unit interval. D/A conversion clock jitter requirements are considrably tighter. A draft AES/EBU standard specifies the D/A converter clock at 1 ns jitter; however, a theoretical value for 16-bit audio could be as small as 0.1 nsec. Small jitter D/A conversion is implemented by using separate PLL clocks for data recover and DAC and by using a buffering between data recovery and DAC.

In my opinion I seriously doubt you could hear the difference between optical and coax, but I guess some people could if they can also hear differences with different power cords.

Another interesting item related to my earlier post - the bandwidth of this digital channel can go up to 6 MHz. That easily covers baseband video in all flavors so keep those cables quiet.

emc guy

[HDTV Forum]

I dug this up. the effects of Jitter are very well documented and the credit for the initial findings of this phenomena for audio go to Stereophile and Ed Mietner in the early 90's.

http://www.digido.com/jitteressay.html

You will get a webpage. On the left box click on "articles" then "jitter".

Richard F. Fisher

[HDTV Forum]

Richard, hopefully this has improved since 1996 or so when your reference was written.

Here's a quote from another article that indicates improvements in the D/A converters used today:

"Toslink's optical conversion eliminates this interference completely. Talking also with John Stronczer of Bel Canto, at least two respected digital engineers acknowledged that today's D/A chips, sample rate converters and phase-lock loops exhibit inherent jitter rejection far superior to what was possible just a few years ago. Hence RCA's touted jitter advantage should play out as less of a real boon. If a plastic or glass fiber optical link were properly engineered, one should indeed expect smaller rather than greater differences."

This is from http://www.6moons.com/audioreviews/toslink/toslink.html for those wanting to read the complete article.

Who knows - it may be the interface type is unimportant as long as good cables are used.

emc guy

[HDTV Forum]

Check out Stereophile for the last 1-2 years and you will see that while it has improved it is not a "for sure" regardless of how much you spend. I do not know of a comparable way to measure this in a surround decoder and they have not done this as of yet. There was an audiophile company a while back that made a jitter reduction interface between the CD player and the D/A convertor and many other products but they sadly went under and possibly unnecessary now as you point out. As always in audio it all depends and nothing can be just taken for granted - synergy due to lack of standards. Correct and consistent analog audio reproduction beyond headphones is yet to be defeated and common. It doesn't have the simple scientific discipline of digital where bits are bits. The good news for all consumers is it all works and you will have fun regardless but if you want to push the envelope there are many, many things to take into consideration and this is just one of them. I guess that is why when you go beyond fun it really is a hobby since there is so much to learn about and plenty of snake oil on the way. Fun is obviously much easier so use that optical - I sure do! I only sweat about my 2 channel rig.

Richard F. Fisher