Noise on SAMD51 DAC

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I am using a SAMD51 for an audio application.  There is quite a bit on noise on the signal.  Not horrible, but you hear it.  I have an Adafruit M4 Neotrellis where they really seemed to follow all of the rules in terms of isolating the analog ground plane, although they don't appear to filter the VREFA like I am going to do.  (The Neotrellis just uses the filtered AVDD for their VREFA).  Turns out, the NeoTrellis actually sounds more noisy than my prototype design.

 

Now I am considering moving to an external I2S D/A converter instead of using the SAMD51's built-in DAC, but there is no guarantee that will be any quieter.

 

Does anyone have any design experience in using the SAMD51 for audio that could give me any thoughts on this?

 

 

 

 

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I redesigned my board to try and eliminate all noise going into the DAC, it didn't really help much.  In looking at the specs, we see the SAMD51 has about a 55dB S/N noise ratio.  Dedicated DACs can get up over 100db S/N.  Isolating ground planes and isolating VREFs with ferrites didn't help much.  

 

I am sticking with my design using the on-chip DACs.  If I need better S/N in the future, I will go with an external DAC.