G'day Diego,
Thanks for your prompt reply, unlike my follow up. I note the original thread has been locked so hope this falls in order. The link if not.. https://goo.gl/9QDucZ
The schematics are fairly straight forward and don't deviate too far from that on the datasheet. If you still think they would be of benefit, I can post them.
In short the noise issue appears to be directly related to the low sampling frequency of 8kHz.. If the sampling frequency is increased (48KHz was all that could be managed in this case by design) the odd switching noise disappeared and so to did the hiss / noise. I'm not sure why this is and I was only able to try 48Khz. Any insight would be appreciated?
I'm very certain the artifacts noted in my previous post were being generated by the DAC as there was no other switching signals near the DAC outputs. It was also unchanged when the Din line was tied low. The noise also seemed to be quite low impedance.. loading the output didn't have a significant effect.
Using a higher sampling rate in this case can be tolerated, albeit slightly higher power and a new PCB to take into account the new and more versatile SAI clocking domain. A plus is less stringent anti aliasing filters. Although it would be good to know if this issue is a silicone limitation with the configuration being used or something else.