Why do digital cables sound different?

While it is strictly a matter of semantics, the actual digital out signal from a transport is sent at 2.822 MHz. If one could resonate a cable that introduced a perfect non-reactive 75 ohm load at that frequency, you would end up with no standing waves. Bare in mind that terminating and feedpoint impedances are a LOT more complex than just selecting a 75 ohm cable ( we wish it was that simple ). This would allow the transport to load up easier due to a complete lack of reflections and a clearer signal path to transmit the data, which theoretically should drastically reduce jitter. This takes for granted that the transport and dac would both have nominal 75 ohm inputs & outputs though. This is something that i've been meaning to check into but just haven't gotten around to it. Sean
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Looks like you're right audioengr. I got into an argument with Monstrous Mike one time about Manchester Biphase encoding. He was trying to say there was no digital edge, only FM modulated sine waves. From what I can find, you are right -- the signal is still sent as square waves from what I can tell (but not with sharp edges -- the standard should likely work even if the signal were closer to a sine wave, but with more jitter).

As for who I am Drubin, just an audio enthusiast, who lurks on the audoasylum cable forum under "audioNeil".

Sean wrote:

If one could resonate a cable that introduced a perfect non-reactive 75 ohm load at that frequency, you would end up with no standing waves.

There may be no standing waves to a pure sine wave at that frequency, but you would certainly experience reflections with digital edges. There are only a couple of ways to eliminate reflections with digital signals, including:
1) series terminate (75 ohm driver) into a 75 ohm Zo cable - reflection from the end is absorbed at the driver.
2) parallel terminate a low-impedance driver into a 75 ohm Zo cable using a 75 ohm resistor at the end - no reflection.
3) Series and parallel terminate - (75 ohm driver) into a 75 ohm Zo cable with a 75 ohm resistor at the end - this cuts the signal in half, but eliminates all reflections.

Forgive me for coming late into conversation...

From what ive seen there is a major flaw in the spec itself The #1 contributer of EMI is the rise time. The quicker it
is the more EMI emitted. A common misconception is the Freq
is the culprit not true. Its seems to me that the rise times
are faster than needed for application. If some one knows why they used the 3mhz with a 12-15ns rise time... Please let me know? It doesnt make sense to me. Although those numbers are prehistoric it is asking for excessive EMI with
faster rise times than needed. Typically you would see a rise time more like 30 maybe as high as 80 for that type
of frequency.

Its like saying take 15min to drive to the store (a 5 minute drive) and then RUN in side and try and make up for lost time when you get there.

As far as termination I agree with Audioeng. You have have
termination in place at reciever end. Its the reflection back thats the killer... Backwards crosstalk is evil sh*t in any system.