TOPIC:

Man the "subject" line really does not allow many characters.

Simple question, I think. The DDRC-22D sits between my PC and my DAC.

Is there any point feeding the DDRC-22D with a high quality SPDIF clock? I'm guessing with all the processing it does that the original clocks are thrown away anyway and the device will use its own clocks, basically making the DDRC-22D asynchronous? Please correct me if I'm wrong.

This question mainly stems from the fact I am trying to isolate my audio system as much as possible from my PC, the best way to do that is either optical (free) or an isolated USB > SPDIF converter (expensive). People freak out about optical having terrible jitter etc but will this even matter in the end since the DAC is effectively being fed by the DDRC-22D (via AES in this instance), not the optical source from the PC?

Cheers all

The DDRC-22D is is indeed asynchronous because of its sample rate conversion to 96Khz. As long as it is done properly, it shouldn't be a big problem.
The biggest 'weak point' of the DDRC-22X series is the fact that it has a switched power supply. Replace this by an (ultra) low noise lineair power supply and your unit will sound much better. Why? Because the 24.576 XO is also fed from that same noisy power supply. This XO is also used to resample all digital data to 96Khz. You might know that a clock is an analog signal, and has nothing to do with I and 0's. That's why a clock will benefit a lot from a clean power supply.

I recently replaced the internal 24.576Mhx XO for a Femto Clock. I notice a (slight) difference on the positive side, but not as much as when I switched to the lineair power supply.
One last thing I will test in the future is providing the XO it's own, clean power supply. That's usually what works best. Just need to find the time for it.

Having said this: asynchronous SRC/upsampling (or whatever manufacturers may call it), does have positive influence on the jitter level, but it will never (fully) recover a bad source. Trash in = trash out. So, I would always try to keep the source as clean as possible.
When your PC is you source, I would choose for an isolated connection: Toslink, AES (which is by standard transformer isolated) or the isolated USB ->S/PDIF option.

I agree with rhodes54 about the linear power supply. I have both an SBooster LPS and the Uptone Ultracap LPS1.2 and both improve the sound, the Uptone in particular does a good job.

FWIW I tried re-clocking the output of the DDRC-22D, albeit with nothing too fancy - the W4S Remedy. I struggled to hear a difference.