Digital coax vs. Optical

[Mike Anderson]

If I may, I'd like to quote Doyle from Sling Blade:

"If you all don't shutup, I'm gonna go out of my mind!"

As Mark said, it's 1's and 0's people. Digital is a totally different animal than analog. With digital it's either on or off. Is there light coming out of your optical cable? Yes? Good. The cable passes. It works. Here's an idea..look down the end of an optical cable and see which light looks better. That will tell you which cable will sound better. The cleaner the light, the cleaner the sound..right?

I'm a lawyer (not an electrical engineer), but IMHO -- I don't think it's that simple.

Here's a good thread on the topic, with some good links too:

http://forums.slimdevices.com/showth...jitter+optical

[teledynepost]

Why jitter isn't a problem:

http://en.wikipedia.org/wiki/Jitter_buffer

If any bits were to be switched despite having a buffer, the information would probably become meaningless to whatever is reading it and cause the audio to stop completely.

[noddin0ff]

It's digital...as in digits. It's 1's and 0's. The DAC has a buffer to correct timing/jitter. 1's and 0's that encode audible high frequencies are not any different than the 1's and 0's encoding they low frequencies. An optical cable will not pass or dampen any specific frequency. You would have to send a lot of bad bit's down the cable to make an obvious audible defect. That kind of error rate just doesn't happen, and DAC's are designed to mask these errors anyway. A perfect digital signal is a square wave form. You can add a lot of noise and interference and signal degredation to the wave form and still accurately extract perfect 1's and 0's from it, a lot. Transfer of digital signals down optical cables is very very very accurate. If you've ever downloaded a an OS software update you've downloaded as many bits as encode a typical song on a CD. Those bits are transferred over miles and miles of optical cable and copper cable and maybe through the air, through zillions of switches and they arrive perfect. The whole modern world depends on the ability to transmit 1's and 0's flawlessly at much higher rates and greater accuracy than is required to perfectly recreate audio. One requirement of audio is that the bits need to be sorted out in a continuous stream with respect to time. The DAC does this, they have buffers and clocks. Better DACs (with better internal reclocking) do it better, but I'll wager it takes a very rare individual and system to hear it (the reclocking/jitter correction difference, I mean). Your transport also has error correction. Transports do this well too. If they didn't software would never install...


rant...rant...

[teledynepost]

Those bits are transferred over miles and miles of optical cable and copper cable and maybe through the air, through zillions of switches and they arrive perfect.

Very good point.

[edtyct]

With all due respect (and I mean it), these devices are not perfect, although tolerance for a certain amount of jitter is the rule of the day. As teledynepost says, major interruptions in a digital stream would cause audio to drop out altogether, but reflections in cables measured in nanoseconds (often at the termination point, apparently, for toslink) can cause enough jitter to affect a DAC's performance. I completely agree, however, that unless something is seriously amiss, jitter error is inaudible, at least to me and to most other people. However, mainstream transports and DACs do not eliminate jitter entirely. Jitter seems to have been more of a problem for Toslink in its infancy, but so it was in all aspects of digital sound reproduction. Coaxial cables weren't immune from jitter either. But holding impedance steady along the entire transmission line can keep it well in check.

In the 1980s, the electronics industry subjected us to the idea that CD had delivered "perfect sound forever." After all, zeros were zeros, and ones were ones. But we've become much more aware of the variables since then, despite how cut and dried digital events seem to be in the abstract. The transmission of relatively noncritical computer data proceeds with very few problems. But higher-level audio is a much more delicate affair. Although the days of brickwall DACs are long gone, jitter is an ongoing issue for those who measure and/or have high standards, and the learning curve for digital audio has far from ended.

[N. Abstentia]

I just don't see how jitter could even be a consideration in a 3' optical cable. 500 feet? Maybe, but still very doubtful if the cable is properly installed and terminated. But 3 feet? I don't think so.

[noddin0ff]

I agree with a lot of what you say. Jitter does exist, and nothing is perfect. But, as you say the error is inaudible to most. And by most I would estimate that the odds of someone actually having the right gear, the right environment and the right ears to notice it are very slim (especially given that no one has even put forth a reasonable description of what jitter should sound like).

But to bring things back into perspective. Is there any reason to believe that one digital cable sounds different from another digital cable in normal home consumer usage? Absolutely not. Cables don't introduce audible jitter.

[edtyct]

N. Ab and noddinOff,

Just to set the record straight, I agree with you. I was simply discussing jitter as part of the terrain, an interesting and subtle part of it that can affect sound--most noticeably, if at all--when a cable has serious flaws or when it is asked to do something for which it wasn't designed. I don't for a moment think that properly functioning cables, or, I should say, cables operating within certain accepted tolerances, between components in somebody's livingroom will differ in sound because of routine jitter. In other words, two Monster cables in good condition at different prices should not result in appreciably different sound quality under ordinary conditions. As N. Ab implies, only when we push usage to the edges do materials and design choices possibly come into play. In still other words, I don't know what EdGein is hearing, and I fear that many of us will never know.

[noddin0ff]

Well that's resolved. Back to you EdG!

[N. Abstentia]

In still other words, I don't know what EdGein is hearing, and I fear that many of us will never know.

Maybe it's not so much what he heard, but more of what he was smoking when he heard it

Where did Ed/Hershon go, anyway?

[evil__betty]

Where did Ed/Hershon go, anyway?

Don't ask - just enjoy the silience.

[JeffKnob]

Maybe it's not so much what he heard, but more of what he was smoking when he heard it

Where did Ed/Hershon go, anyway?

I don't think he realizes there are other threads besides the home theater one so he probably doesn't even know it was moved in here.

[hermanv]

Most modern designs re-clock the data, making the jitter discussion irrelevant today but it wasn't always so.

The analog reconstruction filter in any DAC basically works by connecting the dots together. There are 2^16 dots in the amplitude (Y axis) direction or 65, 536 possible values. To acheive the same dot placement acuracy (1 part in 65,000) in the X axis (time) requires a bit to bit acuracy of around 8 pico seconds. Before reclocking was common, this level of bit to bit timing error was common in cables and much worse in the plastic optical cables. Glass cables did much better.

In home stereo, the error correction is almost all in the player or transport, bits are mostly just re-assembled and filtered in most DACs. In the public network, there are often 6 layers of error correction and often entire blocks of data are transimitted more than once (invisible to the end user) which is not possible without RAM buffers in a DAC (A Sony patent using a RAM to prevent skips in car CD players)

Commercial data transmission (the internet) is all over glass fiber. Comparing large scale optical transmission over public networks that have layers of error correction and using glass not plastic fiber and which transmitts data that on the whole is not sensitive to bit to bit timing error and a CD data link is irrelevant. They are just not the same.

[noddin0ff]

In the public network, there are often 6 layers of error correction and often entire blocks of data are transimitted more than once (invisible to the end user) which is not possible without RAM buffers in a DAC (A Sony patent using a RAM to prevent skips in car CD players)

Commercial data transmission (the internet) is all over glass fiber. Comparing large scale optical transmission over public networks that have layers of error correction and using glass not plastic fiber and which transmitts data that on the whole is not sensitive to bit to bit timing error and a CD data link is irrelevant. They are just not the same.

yeah, I kind of glossed over that... Well said.

[JBMAudio.com]

I have been confused on this issue until today. Some say digital coax some say opitcal for sound. Eddie has stated that you must have an opital cable for best audio. I have been told that the digital coax and opitcal cables both do the same task and not one is better than the other...signal is just transmitted differently..I got two opinions on this. One was by tech support at Best Buy the other from a tech at Crutchfeild both said exactly the same thing not one is better than the other.. To coax vs. optical...The ONLY way the optical cable could be a better source is if you have to run 25 feet or more from one source to the other. Then the optical light would in essence transmit quicker. I doubt any of us would even notice the difference especially if your receiver has auto or manual "lip-sync" capabilites while watching a movie...music only; no difference at all. Please give me your opinions on this subject and what you ahve experienced. Thank you

It is a digital signal, I.E. 1s and 0s. I prefer coax on runs shorter than 100 feet for cost reasons, that's it. You will be fine with either

[hermanv]

It is a digital signal, I.E. 1s and 0s. I prefer coax on runs shorter than 100 feet for cost reasons, that's it. You will be fine with either

It is precisely the transistion between those ones and zeros that is being debated. Although many debates about cable quality trespass on those areas that are very hard to measure, the time smear of plastic fiber cables is very easy to measure and can easily be seen (after data recovery) even with a relatively inexpensive oscilloscope.

Additionally, the CD players and decoders do not use Semiconductor Lasers and PIN diodes for this task, instead you will find LEDs and phototransistors. Once again generalizing to commercial optical fiber transmision can easily lead one astray, it is not the same.

With older, non clock recovery decoding, the jitter was so easy to hear that an industry to sell an improved solution sprang up practically overnight. (Both better cables and the now extinct Audio Alchemy jitter reducers).

There is much discourse on this topic on the internet by both the engineering community and the audiophile community. I think your dismissal of the problem does an injustice to the complexity of the issue.

I do however agree completely on the advice to use coax.

[JBMAudio.com]

There is much discourse on this topic on the internet by both the engineering community and the audiophile community. I think your dismissal of the problem does an injustice to the complexity of the issue.

I am simply saying that most people will not be able to tell the difference between the two. While coax and toslink have different electrical properties, pro's and con's. The difference is very small when it come down to the actual sound coming from the speakers, they sound the same to the human ear.

[hermanv]

Ah, there's the rub, that "most" people part.

Like many audiophiles I have spent a great deal of money on my system, I wish I had the financial resources to be able to spend more. I find, like many other audiophiles, that I can hear subtle differences.

Some people are quite content with a boom box, I have no problem with that. I get concerned when someone tells the boom box owner that he's smart, there is no difference to be gained by spending more money or by improving his home system.

Obviously not all people will want to invest significant money in their home stereo, but it's important that they decide that for financial reasons, not because they've been told that there is no sound quality improvement available. Many have never heard a truly good system, people who visit me are often surprised at what a difference sound quality makes on listening styles. My wife and I can listen to our system exclusively, just as if we were at a live performance, it is good enough to maintain our interest for hours on end.

[shokhead]

I am simply saying that most people will not be able to tell the difference between the two. While coax and toslink have different electrical properties, pro's and con's. The difference is very small when it come down to the actual sound coming from the speakers, they sound the same to the human ear.

My dog can hear the difference.

[JBMAudio.com]

Ah, there's the rub, that "most" people part.

Like many audiophiles I have spent a great deal of money on my system, I wish I had the financial resources to be able to spend more. I find, like many other audiophiles, that I can hear subtle differences.

Some people are quite content with a boom box, I have no problem with that. I get concerned when someone tells the boom box owner that he's smart, there is no difference to be gained by spending more money or by improving his home system.

Obviously not all people will want to invest significant money in their home stereo, but it's important that they decide that for financial reasons, not because they've been told that there is no sound quality improvement available. Many have never heard a truly good system, people who visit me are often surprised at what a difference sound quality makes on listening styles. My wife and I can listen to our system exclusively, just as if we were at a live performance, it is good enough to maintain our interest for hours on end.

I would be willing to bet that you can not HEAR the difference on any system between a high quality digital coax and a high quality toslink.

[shokhead]

Bet ya cant.