Digital transmission is based on SPDIF standard which transmits data and clock information as an encoded signal usually using PCM, that information is decoded on the Mojo into data and clock signal so it's important that the encoded information be jittered free and not degraded over short distance.
The USB transmission on the other end is a device to device transmission mechanism using an encoding scheme and handshaking mechanism, it is usually stream based so more tolerant to poorer wire as frames are transmitted and decoded from the source to the target device. The target device will reconstruct the data and clock signal from the frame and then feed it to the DAC to be analog reconstructed and eventually band pass filtered to remove any residual high and low frequency signals out of the audio band.I still think you need to keep the USB cable short but it is more tolerant of longer lengths up to a limit.
To make a story short, the short USB cable is fine but an analog cable used as a digital one is just a bad idea. Again, that's just my opinion.
Thanks for your intelligent and lucid explanations. If you don't mind a related question:
Clock jitter -- What is clock jitter? The reason I ask is that in considering different DAPs to use as transports to output a digital signal to the Mojo, I've seen some varying specs for clock jitter on different DAPs, as follows:
AK100 90 ps (pico seconds)
AK120 50 "
AK240 50 "
Question: Does clock jitter degrade the digital signal before it's send out from the DAP? Or are they referring to clock jitter of the internal dac, in which case clock jitter doesn't matter since the signal never reaches the dac (it's been output beforehand)?
If clock jitter degrades the signal before it's sent out, then it appears that the AK100 is not as good a transport as the other two. But would the difference be discernible?
Thx
