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only difference I see between the rp82 and cp72 is no coax on the 72. DOes this come into play at all for any feature or future needs? I am about to buy a receiver w/ 3-6 optical inputs so if there's no diff then I don' t think I need to worry and would rather have 5 disks...


thx,


Rob
 

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People will debate optical vs. coax until the end of time. There is no diffence in functionality or what they can handle. They both handle a digital signal.
 

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Nonsense. Either the bits get there or they don't.


Maybe if you run a thousand meter coax cable through the middle of an electrical power plant you'll develop a problem with interference, but at the 1-3 meter lengths that most people need for home theater applications, any decently-shielded coax cable will transmit a sound identical to an optical cable.


People will argue this forever, with some passionately defending optical cables and other passionately defending coax cables. All while spouting pseudo-science to back up their claims. Don't believe it for a minute.
 

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I obviously can't hear a difference between the two, but I typically go for the coax due to its slightly better durability. However, I have heard that some of the newer designs on Toslink cables are much more durable than the earlier ones which I had tried so perhaps this is no longer an issue.
 

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The best "argument" I've heard in favor of coax is that the use of optical cables requires an additional conversion step (digital to optical to digital to analog, rather than just digital to analog). I think we all know that most conversion processes can introduce errors and may not perfectly convey or translate the signal they receive (e.g., all the emphasis on higher sampling and bit rates in D/A conversion). So in "theory" this extra step may degrade the original signal more than when using a coax cable. Whether you can HEAR a difference is a debate that will likely never be resolved.
 

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I'm no engineer, but I had something strange happen regarding a digital cable. I have a new DAC that I've been playing with over the past few days.


As I understand it, if a digital signal locks in, that's all you need, and the DAC will take it from there. Well, I was comparing the DAC to my DVD player analog output, and was shocked when the DAC sounded noticably worse. I don't mean "lower degrees of resolution" type junk, I'm talking it sounded like someone had put their hand over the tweeter and the midrange was all distorted. The DAC was indicating it was locked in, and sound was definately coming through.


I was using the coaxial digital input and some cheap no name cable. I decided to try a video cable, since it also has a 75 ohm resistance like digital coax. Switching to that cable got the DAC sounding fine.


Now, why did that happen? It makes no sense. Was possible inadequate shielding or whatever on the digital cable responsible for the analog output's problems?


So, engineers, explain it please.


Mike
 

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Quote:
Originally posted by otzdig
I'm no engineer, but I had something strange happen regarding a digital cable. I have a new DAC that I've been playing with over the past few days.


As I understand it, if a digital signal locks in, that's all you need, and the DAC will take it from there. Well, I was comparing the DAC to my DVD player analog output, and was shocked when the DAC sounded noticably worse. I don't mean "lower degrees of resolution" type junk, I'm talking it sounded like someone had put their hand over the tweeter and the midrange was all distorted. The DAC was indicating it was locked in, and sound was definately coming through.


I was using the coaxial digital input and some cheap no name cable. I decided to try a video cable, since it also has a 75 ohm resistance like digital coax. Switching to that cable got the DAC sounding fine.


Now, why did that happen? It makes no sense.


So, engineers, explain it please.


Mike
I don't know the technicals, but I am using a high-end video cable for coaxial as well. I was told it could not be surpassed. I would also be interested in hearing from some knowledgeable posters.
 

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Quote:
Originally posted by otzdig
I was using the coaxial digital input and some cheap no name cable. I decided to try a video cable, since it also has a 75 ohm resistance like digital coax. Switching to that cable got the DAC sounding fine.


Now, why did that happen? It makes no sense.
A digital coax cable is the exact same thing as a 75 ohm video cable. There is absolutely no difference between them other than where you plug them in.


If you were using another type of RCA cable (the red or white strands that are typically used for analog audio connection), those have inferior impedance than the yellow video strand, because the analog sound outputs don't require 75 ohms. The yellow video strand does, however, and so if you are going to use one of these for a digital coax connection you should use that one.
 

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Right, but if the DAC was able to lock in the signal, and decode the signal into analog, and bits is bits, then why did it affect the sound?


That was what I was trying to get at. Does anyone know why this would have an affect on the ending sound?


Mike
 

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Quote:
Originally posted by SayersWeb
I have heard that the optical connection won't pickup noise like a coax can.
Optical eliminates any possibility of a ground loop or EMI pickup on the link, but it's unusual for those problems to crop up on a coaxial digital connection anyway. So most of the time, it really doesn't matter which you use.
 

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Quote:
Originally posted by felthove
The best "argument" I've heard in favor of coax is that the use of optical cables requires an additional conversion step (digital to optical to digital to analog, rather than just digital to analog). I think we all know that most conversion processes can introduce errors and may not perfectly convey or translate the signal they receive (e.g., all the emphasis on higher sampling and bit rates in D/A conversion). So in "theory" this extra step may degrade the original signal more than when using a coax cable.
This is not a real problem in properly functioning equipment, however, and it would tend to be extremely obvious if it were to occur!
 

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Quote:
Originally posted by otzdig
Right, but if the DAC was able to lock in the signal, and decode the signal into analog, and bits is bits, then why did it affect the sound?


That was what I was trying to get at. Does anyone know why this would have an affect on the ending sound?
Improper cable impedance could cause reflections in the cable that could in turn cause data errors. That's why you're supposed to use 75-ohm coax. EMI or a bad ground connection might cause problems with the analog circuitry in the converter. Speculation.
 

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Quote:
Originally posted by otzdig
Right, but if the DAC was able to lock in the signal, and decode the signal into analog, and bits is bits, then why did it affect the sound?
Was this PCM data or another format? PCM data is pretty basic, so if the signal was not getting there, there can be bit errors in the data. Bit errors in PCM data can cause audio anomolies because it is raw data being fed into the DACs. Bit errors in Dolby Digital would cause dropouts because it is a more complex data stream with other information embedded.

It sounds like your cable was bad enough that there were significant bit errors, but some data was getting through. The digital coax (SPDIF) signal is pretty robust, and has alot of headroom for loss and noise, so the signal must have been pretty ugly.

-Bill
 
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