Whats the actual difference between RCA, digital, and optical outputs ?
Aug 12, 2004 at 12:23 PM Thread Starter Post #1 of 13

dj_mocok

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Im just wondering, for a dedicated CD player, which output is the best in terms of sound quality ?
For example, on NAD 542 you can find RCA, digital and optical out there...
Which one will provide the best audio quality, and whats the actual difference between those ? (apart from different plugs..)

That results to another question, why most headphone amplifiers use RCA, but not optical or something else ? so that means RCA must be more reliable type of output then ?
 
Aug 12, 2004 at 2:00 PM Post #2 of 13

Czilla9000

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RCA outputs are analog. Optical and coaxial digital outputs are digital.

Inorder to hear what is on a CD (or any digital format for that matter) it must first be converted to analog, usually via a "DAC" (digital to analog converter). Typically, the DAC is located in the CD Player. When you use the RCA outputs of a CD player you are using the CD player to do the digital to analog conversion. When you use the optical/coaxial outputs you are outsourcing the digital signal for another device (for example, a receiver) to do the digital to analog conversion. Some DACs are better than others, and DACs are designed to convert a specific type of digital format.

The reason headphone amplifiers have RCA inputs is because most amplifiers are 100% analog. They are designed to take an analog signal from the DAC, wherever it is, and amplify it to listening levels while maintaining the intregrity of the sound it is amplifing.
 
Aug 12, 2004 at 2:06 PM Post #3 of 13

tennisets

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There's a big difference actually. When the laser reads the data off of the disc, it is just a string of 0s and 1s. Inside the CD player is a DAC; a Digital to Analog Converter. That converts the digital bits into an electrical signal, which is fed out of the RCA outputs.

However, for the digital outputs, the CDP leaves the bits alone, and doesn't convert them to analog. The bits are sent through either the optical or coaxial output, and go into an external DAC through an identical input. The DAC does the same job that the internal DAC did in the player, and outputs the data throught the analog (RCA) outputs.

Almost all headphone amps use RCA inputs because all they do is amplify (or buffer, as the case may be) an analog signal. The only amps that have optical or coax inputs are a combination external DAC/amplifier.

So in short, if you use the digital outs you need to add an external DAC into the audio chain (which can be better than the internal one). RCA outs send out analog signals which have already been converted by the player's internal DAC. Optical vs. Coaxial depends on the player. Hope this helps!

EDIT: czilla9000, you beat me to it while I was typing (and I was away from the computer)! Oh well.
 
Aug 12, 2004 at 2:16 PM Post #4 of 13

Hirsch

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Quote:

Originally Posted by Czilla9000
RCA outputs are analog. Optical and coaxial digital outputs are digital.


It's necessary to keep the terminology clear. Many coax digital outputs use an RCA jack. That doesn't make them analog.

An analog output is just that. If the signal was digital at any point, it has already been through a DAC by the time it reaches the analog output. In 2-channel setups the analog outputs will be paired (right and left channel). Analog outputs can also be balanced, using an XLR connector.

Digital outputs carry a digital signal, oddly enough. If using the S/PDIF format, it will normal use an RCA jack to connect to a coax cable, although a BNC jack is also possible, and has a theoretically higher bandwidth. Optical connectors can also use an S/PDIF digital format. The connectors will be Toslink, or perhaps mini-optical. Digital output might also be be balanced, using the AES/EBU standard, in which case it would use an XLR connector. There are many other possible permutations.

The take home message is not to confuse the physical connector with the type of signal that is going through it.
 
Aug 12, 2004 at 2:23 PM Post #5 of 13

Hirsch

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Quote:

Originally Posted by dj_mocok
Im just wondering, for a dedicated CD player, which output is the best in terms of sound quality ?
For example, on NAD 542 you can find RCA, digital and optical out there...
Which one will provide the best audio quality, and whats the actual difference between those ? (apart from different plugs..)

That results to another question, why most headphone amplifiers use RCA, but not optical or something else ? so that means RCA must be more reliable type of output then ?



This is all going to depend on the quality of the circuits involved. No easy answer. If you have an excellent external DAC, then using a digital output to connect to it might produce the best sound. If your player has an excellent DAC, then using the analog outputs and forgetting about the digital signal might be best. However, both players and DACs have analog sections after the D to A conversion, so a bad analog output can offset any sonic gain produced by a good DAC... it's never easy
tongue.gif


Most headphone amps amplify in the analog domain only. The most common analog format is unbalanced, with a single hot lead and a ground return. The common standard for this kind of signal is the RCA jack. Higher priced gear might use a balanced signal for analog. This can result in more common noise rejection, and would use XLR jacks. I wouldn't say either is more reliable. Each is the right one for the job it is supposed to do.
 
Aug 12, 2004 at 4:08 PM Post #7 of 13

chris719

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Coax is usually superior to toslink (optical) because there is more jitter due to the fact that the toslink transmitters aren't very good generally and there are two more IC's in the way of the signal also. A glass (vs plastic fiber) cable can help but it is still not as good as coax most of the time. There was a thread on diyaudio.com a few months ago with measurements from some audio precision test equipment about this subject actually.

The benefit of optical is electrical isolation which is good if you have problems with ground loops or a very electrically noisy source (ie onboard soundcard). The best way to do spdif would be with a 75 ohm BNC on both ends and matching pulse transformers on both ends also, but this is a rarity on commercial stuff; most use rca's which are not a good impedance match, but it seems to have become the standard.
 
Aug 12, 2004 at 5:31 PM Post #8 of 13

BlindTiger

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I'm impressed that your NAD has analog, digital coax and optical outputs.
Usually it's just analog and one type of digital out. And, I'm seeing consumer DVD players switching to the digital coax instead of optical outputs which is bad for me with a MD recorder.
 
Aug 12, 2004 at 8:17 PM Post #9 of 13

Hirsch

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Quote:

Originally Posted by greenhorn
What about the difference between a digital and an optical output?


Nothing at all. Almost all optical outputs are digital.
 
Aug 12, 2004 at 8:21 PM Post #10 of 13

Czilla9000

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Quote:

Originally Posted by Hirsch
It's necessary to keep the terminology clear. Many coax digital outputs use an RCA jack. That doesn't make them analog.


I know. I didn't want to overload him with info.
 
Aug 13, 2004 at 10:30 AM Post #11 of 13

dj_mocok

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Alright... Lets see... (phew... lots of technical infos coming all at once to my brain.... hope it wont overheat... hehehe...)

So... Let me revise this again, see if i understand this correctly..

- So inside the CDP, the lens will read the data as strings of 0 and 1s, and then the D/A conventer inside the CDP will convert the data into electric signal and pass it to RCA output ? (This is when you are using RCA output)

So basically, the difference between high end (good) CDP and lower end (okay CDP) is, the better CDP will either reads more details, reads more 0 and 1 than low end CDP... and it can also mean that the better CDP will have better built-in DAC, so the end result (the output) will be better as well?

- And basically from what Hirsch said, that means that if you wanna start to jump into external D/A conventer world, then you'd better know your stuff well, or else the change will be subtle or even worse, decreasing the sound quality compared to using the CDP's inbuilt D/A converter ?

So that means i have to really know how good is my CDP's D/A converter, and how good can the CDP transfer the digital out, and also how good is my external D/A conventer is, and also how good is the connection of that external D/A converter is...?
If you are doing your own selections (not choosing by combo suggestion), thats a helluva task i reckon... hehe..

- If you are using your CDP's digital out, that means that the CDP will automatically send the infos right to the output and will not convert it to electrical signal?

Did everything i say was correct so far ?

Anyway, this is the brochure about my CDP... Since you guys understand the technical terms and those D/A stuff much better than me, could you tell me how good is the parts inside there ?

Thanks...
smily_headphones1.gif
 
Aug 15, 2004 at 7:13 PM Post #12 of 13

Jasper994

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Your NAD is supposed to be a pretty good CDP. Unless you put a better DAC downstream, just let it do the DA conversion.

BTW, balanced connections can also come in the form of a 1/4" TRS connector which you'll see quite a bit of in pro audio gear. A perfect example of this is the E-MU 1212m the analog outs are all 1/4" female connectors. You can either use 1/4" TS (unbalanced) or 1/4" TRS (balanced) to connect to your downstream gear.
 
Aug 16, 2004 at 12:21 PM Post #13 of 13

dj_mocok

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i dont think im ready to jump into external DAC world yet... im not that experienced yet and most importantly, my wallet is not ready yet, hehe...
very happy with the nad though, im just curious and wanna know opinions from people who knows about the DAC and stuff (and the system inside the nad)...
 

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