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Topic: optical vs coax (Read 6831 times) previous topic - next topic
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optical vs coax

i am in the process of tweaking my new media center. a pc as source feeds the receiver via these connections:
a) optical
b) coax
c) ethernet

today i connected the coax cable and wondered why it obviously sounds different from the optical connection. i thought my mind is playing tricks on me but i am sure it is something else. either way the receiver shows digital so the signal being transferred from a lossless source should come out perfectly. what else could make a difference in sound quality?

the coax cable says it is suitable for hifi & video connections. it is declared as 75 ohm. a product of hama.
the optical cable is a product from amazon.

i've read somewhere that optical cables can have up to 7 times higher jitter. although it is not said that one can hear that. could the coax cable have more or less damping? i refuse to believe that there couldn't be a reasonable explanation, i am just searching for it  the last and most difficult difference could be the receiver processing the signals in a different way depending on the input.

br

optical vs coax

Reply #1 –
Quote from: foo_on_air on
i am in the process of tweaking my new media center. a pc as source feeds the receiver via these connections:
a) optical
b) coax
c) ethernet

today i connected the coax cable and wondered why it obviously sounds different from the optical connection. i thought my mind is playing tricks on me but i am sure it is something else. either way the receiver shows digital so the signal being transferred from a lossless source should come out perfectly. what else could make a difference in sound quality?

the coax cable says it is suitable for hifi & video connections. it is declared as 75 ohm. a product of hama.
the optical cable is a product from amazon.

i've read somewhere that optical cables can have up to 7 times higher jitter. although it is not said that one can hear that. could the coax cable have more or less damping? i refuse to believe that there couldn't be a reasonable explanation, i am just searching for it  the last and most difficult difference could be the receiver processing the signals in a different way depending on the input.

br



Quite possibly your mind playing tricks on you.  Why are you 'sure' it's something else?


optical vs coax

Reply #2 –
It is not likely that optical and electrical (coax) do something to the bits.
The advantage of optical is that it completely isolate the PC and the receiver galvanic.
But the optical circuit is slower than the electrical one.
This makes it harder for the receiver to detect the rise and fall of the signal properly.
Hence optical will generate more input jitter.

Secrets of Home Theater and High Fidelity compared the coax and the Toslink out of an OPPO BDP-83SE.





Indeed there is a substantial difference in the amount of jitter produced by both connection.
However in absolute sense the values are very low.
Of course the pictures above say something about the product tested only.
It is possible that het values produced by your PC are substantial higher and become audible in the process.


TheWellTemperedComputer.com

optical vs coax

Reply #3 –
TOSLink is a very "lossy" transmission medium, i.e. it degrades the digital signal quite rapidly, and for long-distance transmission - dozens or hundreds of feet - coax is a much more robust medium.

However, at the usual 6-20 foot lengths found in a consumer home entertainment environment, there should be no practical difference whatsoever, considering the relatively low bitrates involved.

If you really are hearing an audible difference, something is wrong.

As a sanity check, can you connect a pair of analog outputs from your receiver ("tape out", "preamp out", or something similar) to the line input on your PC's sound card and do a loop-back recording?
"Not sure what the question is, but the answer is probably no."

optical vs coax

Reply #4 –
Quote from: foo_on_air on
i am in the process of tweaking my new media center. a pc as source feeds the receiver via these connections:
a) optical
b) coax
c) ethernet

today i connected the coax cable and wondered why it obviously sounds different from the optical connection. i thought my mind is playing tricks on me but i am sure it is something else. either way the receiver shows digital so the signal being transferred from a lossless source should come out perfectly. what else could make a difference in sound quality?


I've compared the jitter in optical outputs versus cox outputs on many occasions and found negligable differences.  The means you seem to be using to compare - sighted evaluation - is well known to be highly misleading on many occasions.

Quote
the coax cable says it is suitable for hifi & video connections. it is declared as 75 ohm. a product of hama.
the optical cable is a product from amazon.


It should be just fine.

Quote
I've read somewhere that optical cables can have up to 7 times higher jitter.


The inverse is also true. It's all about chosing what you compare.

Quote
although it is not said that one can hear that.


Jitter is audible if strong enough. However, it is often obsessed over when it isn't strong enough to be heard.

Quote
could the coax cable have more or less damping?


No. Whether or not the coax is ringing is based on its chraracteristic impedance which is always close enough for cables only a few feet long.

Quote
i refuse to believe that there couldn't be a reasonable explanation, i am just searching for it  the last and most difficult difference could be the receiver processing the signals in a different way depending on the input.


It is possible that the reciever is processing the inputs differently, but that is unlikely. Usually there is a phototransistor that converts the optical input back into the same signal that comes out of the coax, and it is very simple and almost always performs flawlessly.

The most likely source of audible differences in this case is listener bias. but I'd like to back that judgement up with some measurements.

We could probably do something with your PC, and the Audio Rightmark program to see if there is serious cause for concerns.

optical vs coax

Reply #5 –
thank you for the useful answers. i am really interested in solving this. if we can rule everything else out i am willing to believe that my mind makes the difference. although i don't think that now because i didn't start the comparison biased.

another simple yet very plausible reason could be that there is a difference in the level, or is this impossible? maybe the level on the optical is a bit higher, hence the signal stronger and the volume higher. it has been tested more than once that humans perceive louder signals as of better quality.

which cables do i need to record from the analogue output(s)? do it use rightmark audio analyzer? a specific song?

optical vs coax

Reply #6 –
My preamp (really my dolby decoder, but that's where the digital inputs are)  will maintain different settings  (stereo, pro-logic, "jazz club", etc) for each input.  Maybe you have something like that going on?

optical vs coax

Reply #7 –
Checking “configuration” in the Win sound panel is another one.
If one is set to eg. Desktop and the other to Full Range they do sound different.
Check the "enhancements" too
TheWellTemperedComputer.com

optical vs coax

Reply #8 –
Quote from: DonP on
My preamp (really my dolby decoder, but that's where the digital inputs are)  will maintain different settings  (stereo, pro-logic, "jazz club", etc) for each input.  Maybe you have something like that going on?

I have ruled that out. The interface is not intuitive but I run it in pure audio mode where every enhancement is disabled.
 

optical vs coax

Reply #9 –
Quote from: Roseval on
Checking “configuration” in the Win sound panel is another one.
If one is set to eg. Desktop and the other to Full Range they do sound different.
Check the "enhancements" too

That's a tough one. I have disabled all enhancements for the sound device. But I don't know how I could set different parameters for the different digital outs. There is only one soundcard.

optical vs coax

Reply #10 –
Quote from: foo_on_air on
I have disabled all enhancements for the sound device. But I don't know how I could set different parameters for the different digital outs. There is only one soundcard.


By disabling them you have already done the right thing.
If you don’t see 2 different devices(Optical and coax) there is simply nothing to configure
The sound card probably takes the same stream and feed it to both the coax and the optical out
TheWellTemperedComputer.com

optical vs coax

Reply #11 –
could someone guide me through the process of testing the output via rightmark aa?

optical vs coax

Reply #12 –
Quote
another simple yet very plausible reason could be that there is a difference in the level, or is this impossible? maybe the level on the optical is a bit higher, hence the signal stronger and the volume higher. it has been tested more than once that humans perceive louder signals as of better quality.
With digital data, the signal level has no relationship to the volume...  If the signal falls too low, the ones & zeros can be corrupted and the sound will be messed-up...  It won't simply lower the volume. 



Each bit is either a 1 or a zero...  There are no fractions or decimals.*  If the level is high enough, it gets interpreted as a 1, and if the level is low enough, the bit is interpreted as a zero.

I don't know the details S/PDIF (or how the optical levels are measured), but here's an example  how TTL logic works -
With the original 5 Volt TTL logic, 5 Volts is considered 1, and 0V is considered zero.  But, if you look into the actual specs,  there are 4 threshold levels:
For a logic input, anything greater than 3.3V is a logic-one, and anything less than 0.8V is a logic-zero. (Anything in-between is undefined, and will never happen in properly functioning circuits).
For logic outputs, a logic-one must be greater than 4.7V, and a logic-zero must be less than 0.2V.

Since the output specs are tighter than the input specs, there is no ambiguity (assuming no defects).

This is the beauty of digital data storage & transmission...   There are billions of bits in your computer and it's very rare that even one bit goes wrong.  The only way to get an error is if a bit gets "flipped" (from 0 to 1 or vice-versa).  And, when a bit/byte does get corrupted, there is often error correction so you never see the error.  If there are any spelling errors in this message, it's not because of "weak" data going over the Internet.     




* Of course, you can represent fractions or decimals, and I can write "1/3rd", but everything in the computer (including this text) is stored as ones & zeros.