Looking for help understanding clock usage in my system

Truly, I don’t get the purpose / benefits of a DDC.  Please explain if you will!

@fastfreight The purpose of a DDC like the Gustard U26 is to effectively elevate digital signal quality/integrity by isolating, regenerating, and clocking the digital signal. To achieve this, better DDCs have their own low-noise power supply, isolation circuit, digital converter, and low phase noise clocking platform. 

Removing galvanic source noise and converting the signal to a synchronous digital format that is locally clocked by the DDC minimizes the influence of both source and DAC on signal quality. As such, a good DDC can effectively improve the perceived performance of various source components and DACs.

@fastfreight @ted_b Thank you for the responses!

I'm inclined to try the U26 without the external clock.  It is a considerable step up from the U18.  Maybe the clock is of no benefit with it.

I simply hooked the ock-2 clock to everything with a clock input with the notion that everything should be clocked the same.  Just because I don't understand it.  As you mentioned, the clock to dac is not doing anything with i2S (I didn't know this). 

I had read that the square wave output of the ock-2 was edgy sounding to some people, but I didn't think so. 

Would there be any benefit to hooking the ock-2 to the N18 Pro ethernet switch if I'm not using the ock-2 for anything else? 

Sorry for all of the stupid questions. 

@sls883  These are very good questions, and you’re far from the first to run into them. I found an instance where Gustard customer service provided clarification to this question, which was published in a Facebook post in a Gustard group. Relatively few DACs have a PLL, and some like the Holo Audio May enable this feature to be toggled on or off by the user, but not in your case.

This is not like in a recording studio, where everything is synchronized to the same clock. Assuming Gustard’s clarification is correct, it seems the only place in this system where the OCK-2 would be the master clock is with the N18 Pro. As for the U26, the OCK-2 should make no difference, but it’s free to try. 

@ted_b thanks again for the reply.

The Gustard X-30 and the U-18 allow you to switch between external clock and internal clock.  But, that doesn't mean that the external clock is doing anything when using the i2S input.

I've reached out to Innuos when I purchased the X-30 and they suggested that I use the ddc rather than going USB straight into the dac.  Gustard concurred.  I didn't ask them specifically about the use of an external clock.  I bought the U-18 and LYH when I was using a Gustard R-26 dac.  I wasn't sure if I needed them with the X-30.  It has a better internal clock.

I also reached out to Gustard and asked if the U-26 would produce better results than the U-18 with the LYH ock-2 and their response was "the U-26 will be an improvement".  I kinda expected them to say that.  

@sls883 If my understanding is correct, this default internal PLL feature appears to apply to R/X/A-26 and later flagship Gustard DACs, so your R26 was the same (whether you realized it or not). 

Innuos has a very good understanding of USB audio concerns, and the Zen Mk 3 has "ultra low noise USB audio output." What you could do is try a direct USB connection from the Zen Mk 3 into the X-30 while using the OCK-2 as an external DAC clock and see how that compares to using the DDC.