Looking for help understanding clock usage in my system

Dump the DDC.

Use the external clock into the DAC., test sine & square, use USB from your streamer.

With USB the DAC's clock (with the help of the external clock) is in charge and you do not have the inherent problems of IIS - with IIS the clock signal is transmitted from the source through the cable - and attaching the external clock to the DAC will not save you from the jitter occurring over IIS connection, the DAC's clock is not used.

Using IIS as a digital interconnect seems to me to be fundamentally flawed - the clock signal is being transmitted over (at least) .5 meters - the connection was designed to transfer data between on board chips!

USB buffers the data and clocking is completely handled by the DAC.

@tutonunez I've listened to a dozen of my reference songs and I'm very impressed with the U-26.  The U-18 and LHY ock-2 are in boxes.

The soundstage is bigger, punchier bass, better separation of instruments, more clarity/detail.  No harshness.  I'm very happy with the X-30 and U-26 combination. 

@tutonunez have you messed with the IIS MLCK rate? It has options of 128FS, 256FS, 512FS, and 22/44 Mhz.  I have no idea what those are. Does anyone else know?

There is also a menu option for DSD flag. FLAF 14, FLAG 15, FLAG 16, and no flag.  I have no idea what those are... 

Hi sls883, the FS refers to the clock frequency coordinated via I2S between the DDC and DAC, which is the master clock. In my case, since I have two DACs, when I use the SMSL SU-X I use 512FS, and when I use Holo Cyan 2 I use 22/44 MHz. This determines the stability and synchronization of the system. I don't have the R30, but I think you should use 22/44 MHz. How can you find out exactly which clock your DAC uses? Connect your DAC to the PC, and XMOS will show you the clock frequency it uses in one of its tabs; that's the one you should select in the U26.

Regarding the DSD Flag, it's only used to designate which PIN the DSD assignment is located on, which varies depending on the DAC manufacturer. However, in your case, that doesn't apply, since you only need to connect the I2S to the IIS-G and the assignment will be automatic because it's between Gustard devices.

I hope that's clearer.

Regards!

@tutonunez Thank you for the reply!  I shot an email to Gustard to see what they suggest for the clock frequency.  They've been good about responding to emails.  If I get a chance, I'll try connecting to a pc.  

I don't know if it's correct, but I found the following information with Google:

For the Gustard U26 to work correctly with the Gustard X30 DAC over IIS (I2S), you should select the 128FS MCLK rate. While the U26 allows you to cycle through multiple rates, 128FS is the standard "native" master clock frequency for Gustard’s current flagship ecosystem (including the X30 and R30) to ensure proper synchronization and avoid playback errors.