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|   Hey Kelsci, Optical vs Coax cables revisited. | KiD SmokE
Jul 29, 2002 1:07 PM | | I did some digging after your post concerning difference you heard between Optical vs Coax cables. For starters, here is what the signal looks like out of DVD player's digital output (Manchester):
<img src="http://www.mycal.net/projects/digital/manwav.gif">
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The above diagram represent an ideal digital signal (no jitter). As you can see, the most important thing here is the clocking. The clocking is taken at zero [volt] crossing (look at Belden diagram).
The clocking will determine when a data's bit ends and where next bit begin. This clocking (timing) is very important. For example if you have a 96/24bit DAC, timing not only tell DAC where the 24th bit end (as to start on next 24 bit..each 24 bit represent an analog value), but also the at what precise second place its analog interpretation along analog X-Y axis (X..>, Y..^)
By precisely placing the analog interpretation of 24 bit in its place, you will get seamless analog representation of analog signal as next analog representation of 24 bit is placed precisely next to it. The end result would be that you will get a analog sine wave that seem continuous (not step motion like).
<img src="http://static.howstuffworks.com/gif/cd-tone.gif">
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Now, let see what happen if jitter introduced into system by transportation system. Lets look at below diagram:
<img src="http://www.haveinc.com/BELDEN/images/tpcbctd1.gif">
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As you can see from above diagram (the crocked solid lines is cause by jitter), the timing is slightly off. Ideally, the zero crossing for clock is at precisely 20, 100 and 180 nanoseconds. But because of jitter, the zero crossing is at 25, 103 and 190 nanosecond. And since 1s and 0s of data are constructed using the clock, the jitter will cause 0 to be slightly longer or shorter than 1s or vise versa which is technically called non-symmetrical (0s and 1s should have be symmetrical..same shape).
Since the timing is off and Receiver's DAC depend on the timing for precise placement of equivalent analog value of digital bits, then the end result (if you look closely at the constructed analog signal) is "step" shaped analog signal rather than continuous (sorry no picture..use your imagination)
Step shape analog signal will not have "high" or "bass" roll off, or any adjective that is associated with analog signal. But rather you will get sound quality that could be describe as smearing, dry, metallic or fatigue sound. |
| KID; acknowledging your post. THANK YOU | kelsci
Jul 30, 2002 11:00 PM | | I will have to study this more. I am not computer savvy but I will attempt to create a file and download this for study. Your knowledge of this is way way above my possible comphrehension.
The smearing, dry, metallic and particulally fatigue sound is something that I have heard in differences between different coaxial cables. The HIGH and BASS roll off was a shoot out between a GE OPTICAL vs a AR OPTICAL. It was the AR OPT cable that exhibited the roll off. |
| Looks like my job is not done yet :) | KiD SmokE
Jul 30, 2002 11:15 PM | | Sorry if I made it too technical. I couldn't see any way around it.
>The HIGH and BASS roll off was a shoot out between a GE OPTICAL vs a AR OPTICAL. It was the AR OPT cable that exhibited the roll off.
I may have dig into this subject and come up with more charts, graphs and technical jargon. Let me know when you are ready for more :) |
| KID, no apology needed, but if you hear about a new volcano..... | kelsci
Jul 31, 2002 12:47 AM | | spewing lava in the South Florida area, it was my brain or in other words, the springs of the CLOCKING mechanism got loose. |
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