I am an engineer, with 30 years digital design experience, so I'll be happy to give you the technical explanations:
1) The S/PDIF output from a transport is specified at 75 ohms characteristic impedance. This means that the output impedance of the transport should be 75 ohms and the input impedance of the DAC should be 75 ohms, as well as the connecting cable and connectors. Mismatches in this impedance can cause reflections that cause jitter, and these mismatches are quite common in even the best transports. I have measured and fixed plenty of them.
2) The slew-rate or rise-time of the S/PDIF digital signal has a large effect on the jitter when the signal is detected at the DAC. All transports have quite slow risetimes by design in order to pass FCC emissions testing with the poorest S/PDIF cable attached and mismatched impedance. Therefore, they cause unneccessary jitter. Some Transports will have slower risetimes than others, but unless they are modded, they are all slower than desired.
This white-paper I wrote details the analysis of why the cable length, impedance matching and risetime are all critical to minimizing jitter:
http://www.positive-feedback.com/Issue14/spdif.htm
Steve N.
Empirical Audio
Manufacturer/modder
1) The S/PDIF output from a transport is specified at 75 ohms characteristic impedance. This means that the output impedance of the transport should be 75 ohms and the input impedance of the DAC should be 75 ohms, as well as the connecting cable and connectors. Mismatches in this impedance can cause reflections that cause jitter, and these mismatches are quite common in even the best transports. I have measured and fixed plenty of them.
2) The slew-rate or rise-time of the S/PDIF digital signal has a large effect on the jitter when the signal is detected at the DAC. All transports have quite slow risetimes by design in order to pass FCC emissions testing with the poorest S/PDIF cable attached and mismatched impedance. Therefore, they cause unneccessary jitter. Some Transports will have slower risetimes than others, but unless they are modded, they are all slower than desired.
This white-paper I wrote details the analysis of why the cable length, impedance matching and risetime are all critical to minimizing jitter:
http://www.positive-feedback.com/Issue14/spdif.htm
Steve N.
Empirical Audio
Manufacturer/modder