The Official (and only) Optical vs. Coaxial Thread

[Enzian]

This is the The Official (and only) Optical vs. Coaxial Thread, right?

The only thing you change is the cable. You use the same equipment. Same brand DVD player, same reciever, same speakers. Give a listen. Change cables. Give another listen. Compare/contrast.
If you'd like, you can change equipment - but don't cross your expirements. If you change eqpt. you need to listen/compare with both cables, again.

And Taxi, while I agree with the spirit of your analogy, I would say spending tons of loot on cables at the expense of better eqpt. is like spending the farm on Mushkin memory for a x286. (yet another debate - Mushkin vs. generic DRAM)

[Dom]

And don't forget the double blind test... which, ultimately, also needs to include listening without a cable... I'm convinced that this, at least, will make for a distinct difference

[Wirehed]

Originally posted by Dom
And don't forget the double blind test... which, ultimately, also needs to include listening without a cable... I'm convinced that this, at least, will make for a distinct difference

indeed. Here I think we can all agree!

[Enzian]

[AirSickMoth]

Also, don't forget to do the good old fake out.

You go behind the reciver and pretend to change the cable... But you don't. You then ask people what the difference is. You say something grand like, "Now give THIS biotch a listen to."

When someone says it is better or worse.....

The test is over because it is too dependant on peoples own biased, influenced, inacurate, personal observations and not quantifiable, scientific fact.



1138, a different comparison for Cable and Cars would be:

Spending a fortune on Cables is like spending a fortune on Car Wax for your Ferrari. It might make it shinnier than the cheap stuff, but it doesn't make it perform better.

[Jellodyne]

The best analogy would be putting $800 hand crafted custom lugnuts on your Ferarri because it 'holds the wheels on better' than the factory lugnuts. They either hold the wheels on or they don't, though the expensive ones may impress your friends and neighbors.

As for the test, I suggest one test where you don't change the cable, but increase or decrease the volume slightly. I'd bet that would be a more significant change than the cable changes.

[Enzian]

Ooo! Jellodyne! Good call with the volume idea!

[PAceto]

If I may add my two cents at this late date, it seems most people are hung up on side issues. I've had a Master's in electrical engineering for over 25 years. I just finished designing a Gigabit router that had both optical (Sonet)and coax transmission. Believe me when I say that bits are bits regardless of whether they are sent over coax or optical cable. If you hear a difference in the sound quality, it is not due to the transmission mode (there are a lot of other things in the total path that have nothing to do with the transmission method). If there is a transmission quality issue that the error correction routine can't correct, the result will be either 1) silence or 2) very loud static (try listening to a data CD in an audio CD player to see what I mean). All other things being equal, I prefer optical cable for two reasons. First, there is no impedance matching problem. Second, there is no electrical connection between the two units eliminating the possibility of a ground loop.

[Enzian]

Halelujah and Amen, brother!

[Dom]

[PAceto]

For those who raised the issue of error detection and correction, I looked through the AC-3 spec (Dolby Digital 5.1) and found some answers. Each frame of data has two CRCs (cyclic redundancy check words). A CRC is like a checksum of the data in the frame, only more complex. This technique allows you to detect errors and correct most of them. There is also another correction scheme further down in the decoding that does some correction. The spec mentioned muting as a possible result of some types of errors. I looked for some mention of frame resend on error but I haven't found it yet. Here is a link to the spec for anyone who is interested: http://www.atsc.org/. Look for the AC-3 PDF near the top of the page.

[Wirehed]

snicker.

We'll see at the test.

[PAceto]

A listening test is purely subjective. Put a spectrum analyzer on it and you've got something.

[Chromy]

That's what I'm talking about Seamonkey says that a certain digital cable gives him more bass... Take a HTPC, or something else that can output a sine wave at on frequency, swap out the cables and measure SPL

Chromy

[PAceto]

Why not use the test tones on Avia? Rather than just give opinions, I've just decided to run some tests using instrumentation from work. I'll check the audio output at both the preamp out (using an RMS meter) and at the speakers (using an SPL meter). I think Avia has individual tones at a variey of frequencies. No more junk science!

[PAceto]

Well I ran the comparison tests last night. Unfortunataly, Avia only has frequency sweeps, not a series of individual tones. Fortunately, they were low frequency sweeps (most people claim to hear better bass on coax). I set up a sound level meter on a tripod at the sweet spot and I ran the front speaker sweep and the sub sweep over and over. At specific frequencies (as listed on the TV), I recorded the levels. I repeated the test with both optical and coax and found absolutely no difference. I also ran the pink noise tests since they were quick to do. Again, no difference between optical and coax. I only wish there were individual frequencies that stayed constant for a few seconds. It would have been a more rigorous test.

[Mr. Furious]

Did anyone create a test procedure yet? I'd be very curious to read it. How are you guys planning to manage the "Placebo effect"? Are you just planning to rule it out statistically?

[PAceto]

Using a sound level meter with test frequencies avoids the placebo effect. Meters don't have a preference.

[1138]

I thought it out some before but haven't given it much thought recently.

I was thinking of something like doing 10 listens in a row of the same clip, switching the cables for each listen. We'd figure out when to switch cables by flipping a coin ten times. Depending on time, I'd like to do maybe even more than 10 just to minimize sample size effects.

I'll think on this more. Anybody else have suggestions for specific procedure?

[Taxi]

Well, some of this we'll have to work out when we get there.

But basically, I was thinking it would go like this:

Everybody who is going to do the listening (ie pretty much everybody I think) sits in room A. Everybody gets pen and paper, with a list from 1-20 (or whatever) to write their answers down on. The person who runs the test plays a clip (10-20 seconds). Then, a pause (while cable is or isn't changed.) Then the clip again. Everybody writes down if they heard a difference, and whether they thought the first clip, or the second clip sounded better.

Repeat this several times. Some times a "better" cable is used the second time, sometimes first. Sometimes the cable isn't switched at all. Tests should be repeated enough times so that each cable is compared with every other cable at least once. (I will be bringing a Tice Audio digital interconnect, as well as Chromy's "monster" cable. ) Of course, all this cable switching is done behind some kind of blinder, or maybe even in another room, so that nobody can see what is going on.

Also, I think the clip should be changed after 2-3 listenings, so that nobody focuses on that one clip. (I don't know if that's scientifically sound reasoning or not.)

So, anyway, once all the tests are run, then everbody can be told what each test was (by number), and whether or not anybody could pick out the high-end cable.

How does that sound? (No pun intended.)

[Wirehed]

Taxi's suggestion is pretty close to what I was thinking.

And someone from the audio shop will be administering the test, so you can just enjoy Taxi.

I have Dom's cable here to test as well. And We'll throw in some nice Top-o-the-line Transparent too.

[brian]

Wouldn't you want to use the same clip? The most important thing science ever taught me was that you should only change one variable in an experiment, otherwise the results could be skewed by the new variable. In this case, only the cable would be changed, and you want people concentrating on that one clip. If there is a difference, you want people to take note of it, and get used to the clip. Its hard to compare say, Pink Floyd music and John Williams, to be able to see if there is a difference in cables.

The only instance you want to change the clip is if you rerun the whole experiment, with the same cables and order as you did the first time, only using a new clip. Then you would see consistencies/inconsistencies between what people hear.

[Taxi]

brian: I do think that the clips should always be the same when actually comparing two cables. I would suggest though, that when a different set of cables is compared, that using the same clip EVERY time could skew the results, since I would think you'd naturally compare what you're hearing now with what you heard during the last test. (Gee, this one sounds better than the last two.) By switching clips every few tests, you are forced to concentrate on what you're listening to, since it's not the same thing each time.

So, just to be clear, cuz I think I'm not being clear...

Test 1

Cable A -- Cable B <-- Audio Clip 1
Cable C -- Cable C <-- Audio Clip 1
Cable B -- Cable A <-- Audio Clip 2
Cable D -- Cable A <-- Audio Clip 2
Cable C -- Cable B <-- Audio Clip 3
Cable B -- Cable B <-- Audio Clip 3
Cable A -- Cable D <-- Audio Clip 4
Cable A -- Cable C <-- Audio Clip 4
Cable C -- Cable D <-- Audio Clip 5
Cable D -- Cable A <-- Audio Clip 5

Something like that. We should try to work some of this out on Friday night.

[Enzian]

That sounds good Taxi! I can;t wait to "hear" your opinions!

I think there should be
For X = A to D
Cable X -- Cable X test
End For

[Taxi]

Enzian: Well sort of...

I think what you meant was

For X = A to D
For Y = A to D
Cable X -- Cable Y
Next Y
Next X

Otherwise we'd always be comparing the same cables to each other.

(And yes, I agree. I just didn't want to type it all out. )

[Wirehed]

heh, what a bunch of geeks we are.

[evancich]

If you want this test to stand up to scientific rigors, then you should measure with orthogonal sensors. When you guys run this test, add a spectrum analyzer and a sound level meter. These are sensors that give hard data, data that cannot be argued over if the sensors are setup correctly.

Also, list your assumptions, for example:
1) TOSLINK and DCoax have the same output level (that is, a the same bit pattern thru each cable will generate the same wattage at the speaker)
2) The receiver you are using is NOT skewed to one input or the other (that is, Tosh equipment would probably not be good to use…)

[Ruined]

Optical vs Coaxial?

Even the very best Toslink optical cable (the optical interface that consumer devices use) pales in comparison bandwidth-wise to any cheap, properly made 75ohm coaxial cable. Yes, RCA cables could be subject to RF interference, but if the cable is designed well with proper shielding the digital signal should not be affected in the slightest. Not to mention that optical cables are far more fragile than coax cables, and more pricey as well. To sum up, a $400 Toslink optical cable is inferior to a $15 Radioshack Gold 75ohm coax cable. It hurts, but it's the truth

NOTE: Dolby Digital/DTS (the bulk of home theater material) should not be affected at all by cabling, due to its packeted nature. With DD/DTS, it either works or it drops out. On the other hand, PCM (CD) transmissions can actually sound less pleasing to the ear without dropouts when using poorly contstructed cables. It is also worth noting that when concerned with PCM digital transmission that the cable is not the only thing to consider. The source (such as the CD/DVD player) and the destination (such as the receiver/prepro) can both also contribute to how accurate the final PCM sound is after your receiver/prepro is done with it compared to the PCM track on the original CD.

My advice? Go with a well made 75ohm coax cable. It will last the longest and cost you the least. Plus, if it makes you feel better it is capable of much higher bandwidth than Toslink optical offerings. So go buy that $10-20 Radio Shack Gold Video/Digital cable or maybe if you want something that looks a little nicer and is built noticably better you could snag an AudioQuest VSD-1 ($25) cable. Anything more is a waste of money.