A "bit" of information

my marantz 5 disc cd changer sounds VERY different(like crap to be exact) from my dvd player when both used as transports with my Bel Canto DAC2, with Philips $65.00 dvd player being a clear winner. And WireWorld Super Nova 3+ glass toslink sounds way better than the $25 Monster coax when fed into the dac from same dvd player, and I am not the only one to confirm this in my own system, just for those who beleive all digital cables sound the same. go figure.....

Pondering your question got me thinking about optics, like the ones in cameras. Precision optics render sharp images. Dull optics produce errors, particularly at the edges. While maybe irrelevant to CD transports, the precision concept by itself may not be. The transport conveys electrical or optical representations of the ones and zeros, not the numbers themselves. Because the transport performs a translation of the pits and lands embedded in a CD, how well it achieves this feat becomes important. From the responses you can see that not all transports are created equal.

But more to your point, and processing considerations aside, in any piece of audio gear the quality of the parts used, their stability over time, the quality of assembly and the rejection of outside influences like vibration and radio interference, along with cosmetics, play a role in decision making too.

Welcome to the real world Neo...

Koestner, in my opinion, although some dacs claim superb jitter rejection, their ability to deal with certain amount of junk that comes in from the transport is important. I personally don't think that Benchmark DAC-1 or my Bel Canto DAC2 are so jitter immune. They probably are better in this regard than some other dacs, but again it all depends on how much of that junk that comes in they can deal with. Recklocking the signal could be affecting other aspects of the dac's performance, making overall impact on the sound. I think that the cleaner the signal from the transport, the better the dac's overall performance. Also, this is where a good digital cable comes in. I seem to agree with Rockvirgo
here, it's just like a lens on the camera. Better transmission of the signal, that's all. Just speaking from my experience, this is how I picture it.

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