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Discussion Starter · #1 ·
I'm curious as to if it really makes that much of a difference as to which type of cable to use for the digital out on DVD players.


Does using Optical cables have any benefit over using Coaxial?


Thanks

Greg
 

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I've heard that "serious" folks prefer coax. One of the reasons I've heard for why is because when an optical cable moves or shakes around (I guess when you're listening to something loud) it can cause slight variations in the signal.


Both are just trying to send 1's and 0's on the line, and do it in different ways. Optical cables could have poor signal transfer characteristcs, dimming the light or whatever, causing the bit to show up a little "off" down the line. But then you have the coax, which can be succesptible to electomagnetic intererence, which can cause the bits to be "off" a little down the line.


I'd probably prefer coax more than optical, because it's all digital and electronic. You don't have to worry about the response time of your LED on the sending end and pickup (a photodiode or photoresistor maybe?) on the other end like in an optical setup.


Not that I noticed (or even cared to notice) a difference when I moved my DVD player from optical to coax to make room for a new TiVo unit.
 

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I would prefer coax for the simple reason that any RCA terminated cable can be used and is thus less expensive. The endless debate rages as to how much one must spend to get a signal that is "good enough". It's a matter of what you can actually hear. OTOH, I will be connecting my soon-to-be purchased DVD player to my Rotel DD decoder using the optical connector. This, simply because the decoder's two coax inputs are already occupied by devices that only have coax outputs. The optical input is vacant.


[rant]

It absolutely escapes me as to why the geniuses at the companies making these latest-and-greatest DVD players with built-in DD/DTS decoders and 5.1 outputs have failed to present at least one lousy coax input on their machines. I guess they figure tht everyone either has two 5.1 inputs sets or a digital input on their preamp, and those that do would rather use the preamps decoder. This is especially an issue if you want to add DVD Audio which must be decoded in the player and you already have an outboard 5.1 decoder. Arrrrrrrggghhhhh!

Sorry.

[/rant]
 

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I asked BetterCables about the differences. They say the connectors for many optical cables are not a very high quality. Give BetterCables a call and you'll probably get a better answer.

It also seems impossible to get 12M long optical cables, which I was looking into at the time.
 

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iodine23,


I love your interpretation of "jitter" (as the cable moving around, not quite...).


OK, the theory goes like this:

1. There's line jitter - i.e., digital signals go in through sampling, if you sample at an asynchronous rate, you can "miss" samples. Jitter means that the clocks are asynchronic and this can theoretically add "digital noise" to the signal and lose data. Data processing theory states you're supposed to sample at 2x the data rate, but that's not always the case (and occasional mis sampling can still occur at 2x sampling frequency).


2. There's bandwidth, the bandwidth of fiber is lower than coax. That means transition time from "1" to "0" is slower than coax.


3. Coax is susceptable to EM/RF noise, which can introduce errors into the data stream.


4. Fiber is a "Go/no-Go" type of connection.


5. There's error correction (except in PCM, but who uses that except in regular CDs) that's supposed to bypass these noises. The theory goes that the error correction works, but slight degredation of sound is possible if there's enough noise on the line (from line jitter, mis-sampling, or electronic noise).


6. No one has objectively shown any differences between coax and fiber that I'm aware of (I asked "Secrets of Home Theater" to run a test on this a couple of weeks ago, but they have not answered me).
 

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I wasn't refering to jitter in my response, I don't think I even mentioned the word anywhere. I was pointing out that I have read an article talking about how some feel optical is more inferior because it can be affected by the cable being vibrated around. Since coax is just an electrical connection, you can move the cable all around and it shouldn't matter...


Though you really know that a length of cable has the potential to act like an antenna, and moving it around through space could induce currents in the cable, causing noise. But the movement is so minute that the currents induced are minute and so no perceptible noise is introduced by a coax cable vibrating. I'm sure the case is the same for the a vibrating optical cable and connector.
 

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Since the Digital Signal starts out as Electrical

U have to Convert2Light & Light2Electrical at the other end.

So not Only is it How good is the Optical Cable..But how good are the Conversions

Not 2 mention 2 more Circuits (more is not always better)


That being said:

I like the SOUND from my STB/JVCDVD optical Monster 1m ->Sony STR-DA777ES

Better than the HTPC/CMI8738 coax AR 8m gold plated.....->Sony STR-DA777ES

But only notice the Difference when I switch over


So once again it's all in the EARS of the beholder
 

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For me the answer is to use both at the same time. From the RP91 DVD player which now sees double duty as a CD transport (I like the remaster feature), I have connected the optical to the CD jack and the coax to the DVD jack on my receiver. The benefit of this is that when I select "CD" or "DVD" on the receiver remote, I immediately get the appropriate stored receiver settings for that format. Great convenience feature.


BTW, this also allows you to do an easy A/B comparison of optical vs coax. Just set the receiver up the same way for CD and DVD and play something while switching from CD to DVD on the remote. I tried it and I couldn't hear a difference.


Cheers
 

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Iodine,


Electrical noise and static-electricity or friction-noise (those small electronic noises caused by friction or movement) would affect coax, certainly not an optical technology.


There's no electrical connection anywhere on the fiber connection. It's a purely light driven connection.


Either you have a carrier (i.e., you see the light) or you don't. Little "movements" can't cause any such affect as you are describing. It's like saying that when you flush your toilet, the lights in your neighbor's bedroom grow dimmer...
 

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Discussion Starter · #10 ·
Thanks everyone for your replies. My DV-47A just arrived and I already have a Coax from my Toshiba SD-3109.


I'll see how the similar wiring works with my new SD-643HD5. I've gotta go out now and drop close to $200.00 on new cables for the 5.1 audio to the external decoder on my Yamaha RX-Z995. And those aren't the top of the line Audio Interconnects.


If I can wait on the optical cable, or if it does not make that much of a difference, I'd rather put the money toward the last piece of this upgrade, which is a decent remote.



You guys are Gr8t


Greg
 

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About the rant of why DVD players with DTS decoders don't have coaxial inputs... this actually isn't a trivial feature to implement. It is not physically possible to just connect a coaxial input to the average DVD decoder/controller setup, and decode audio from it. The incoming audio stream is not packaged the same way as the one coming off a DVD. You have to be able to get it out of IEC 1937 packets, and you also have to be able to handle timing differently.


When playing a DVD, the system has an internal clock to control time. You throttle the speed of audio and video decode to match the clock. But when taking digital input, you have to be able to decode and play the stream as fast as it comes in. There will be slight fluctuations of input speed relative to your output frequency. So you have to buffer a bunch of input, and nudge your output frequency a bit to keep the buffer from overflowing or underflowing.


For an example of the challenge, let's say your receiver is playing PCM audio from a CD. But, the CD source is a DVD player using an ESS decoder chip. CD is supposed to play at 44.1 kHz, but ESS chips have been known to play it at 44.2 kHz. So the receiver has to detect this, and adjust its output frequency to 44.2 kHz. Because a slight frequency error sounds better than having to discard some input because it arrives at a higher rate than you can play it.
 

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Ian, thanks for the input. I didn't intend to trivialize the effort required, but there are inexpensive prepros that do this and much more. I guess that I'll have to have the DVD-Audio mix down to stereo and connect those analog outputs to my Rotel preamp. Then have the optical out connect to the Rotel DD decoder. If I want surround DVD-Audio, I'll either have to live with the DD interpretation or manually switch some cables. Of course, I could always plunk down the 200 clams for that 5.1 switch that someone pointed out here the other day. It just makes ya cranky. So close, and you have to come up with another grand or two to get it right. Grrr.

Peace.
 

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oferlaor:


This may be an exaggeration, but if I shine a laser beam right at your eye, and then move it a little to one side and it's hitting your cheek, do you register the same brightness of the beam? No.


Of course this shouldn't be happening at the end of the fiber because the pickup should be very close to the end of the fiber. But my point was that by moving the connector just a little the beam's focus point may move, changing beam intensity, and therefore changing the behavior of the converter turning the signal back from light to electric.


Personally I think it's all kind of silly myself, but I'm just hypothesizing from an article I read claiming that some "audiophiles" didn't like optical because physically moving the cable could alter the signal... they just didn't state why. I can't imagine it would change it so much that you would notice it... but I've also read lots of sillier claims about expensive cables and transports and all that stuff. I'm personally doing just fine with my cheapo optical cable that cost about 20 bucks.
 

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Quote:
Originally posted by Ian Montgomerie
When playing a DVD, the system has an internal clock to control time. You throttle the speed of audio and video decode to match the clock. But when taking digital input, you have to be able to decode and play the stream as fast as it comes in. There will be slight fluctuations of input speed relative to your output frequency. So you have to buffer a bunch of input, and nudge your output frequency a bit to keep the buffer from overflowing or underflowing.
I don't understand this. Especially the last two sentences. What is a fluctuation of input speed? Input to what? Speed of what?


Are you trying to say that there can be packet jitter at the digital input? What do you mean by "output frequency," the decoded data rate?


I'm an electrical engineer, so lay it on me if you really understand it.
 

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iodine23,


It's obvious you know nothing of electronics or fiberoptics (no offense, this is just my observation).


Oposite the laser, is a light sensor. The laser basically has to point towards it. There is a tolerance there for the brightness of the beam. The beam turns off and on to allow for "1" and "0". If the connector is bad and the "1" is too low, NO SOUND will be coming out of the unit. That's what we call "go-no-go". Either there's a link or there isn't one.


I'm tired of explaining this & you not getting it. Think what you like. Moving lasers, cheap fiber, whatever...
 

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Bottom line is if you get NO DROPOUTS you are getting the highest quality audio period (no matter how expensive the cable or whether it's Optical or Coaxial)! Cables do not enhance digital signals at all and if there is any bits being delaye etc.. you don't get dimished audio you get dropouts. To many people are still living in the Analog world and tend to apply Analog rules to Digital which is not appropriate as they act in a totally different manner.


As to which cable... if you can use Coaxial use it first as it's cheaper for the cable if not then any optical cable will do. If you get dropouts you know the cable is bad but I myself have yet to encounter a cable causing dropouts and being bad at any time.
 

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oferlaor:


Actually I have a masters degree in electrical engineering and have built a circuit on a robot utilizing a laser and photodiode as a pickup (I'm not sure if that's how optical audio is setup, though). So your observation is wrong.


If there's a brightness tolerance, then I can accept your arguments. Makes me wonder why companies, like Monster Cable, pitch their high quality optical cables with a spring loaded connector for "precise alignment" and stuff then... if you say alignment doesn't really matter (or that it's built into the tolerance). Though it wouldn't be the first time a marketer put a lot of spin in to relieve your wallet of your money.
 

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My reciever supports 3 coax and 3 optical on the back + 1 one the front. Since optical seems to be more prevalent than coaxial, I am choosing caxial for new equipment. My optical ports are all taken.


I've got plenty of experience with the electronics and personally don't think that it matters much for standard connections. If you have a component in the chain with high BER or a crappy clock and bad retiming, you might hear an increase in the noise floor or some wierd low level tones if the PLL is hunting, but this shouldn't occur in well-designed equipment.
 

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Quote:
Originally posted by iodine23
Makes me wonder why companies, like Monster Cable, pitch their high quality optical cables with a spring loaded connector for "precise alignment" and stuff then... if you say alignment doesn't really matter (or that it's built into the tolerance). Though it wouldn't be the first time a marketer put a lot of spin in to relieve your wallet of your money.
Monster is a company that really sells marketing claims rather than cables.
 

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kelliot: It seems like sometimes that's easier said than done. I'd love to get a new RP62 or something along those lines, but they're optical only. I guess I could get a converter... cuz I'm in the same boat as you. 2 optical, 2 coax on the receiver. Optical is taken up with PS2 and TiVo, optical only. My current DVD player is coax and optical, so I moved it to coax. But any new components have to be coax, converted to coax, or I have to get a new receiver.


As I said earlier, and to stay on topic, I didn't notice any difference at all when I moved the DVD from optical to coax.



gabe: Yeah, it's a lot of claims. Too bad Monster's PS2 optical cable that I picked up doesn't have those "precision alignment" spring loaded connectors. The cable connector doesn't even lock into the optical port on the receiver at all, it can slip out very easily. I'll get the most out of my game with another brand of cables next time. :)
 
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