Lower noise with USB to S/PDIF to I2S

[Skip Pack]

I was making an I2S DAC for a friend of mine. He is old school, and uses a CD transport with S/PDIF output to an external DAC.  

I used a DIR9001 module to convert S/PDIF to I2S. I needed to test this, and I don't have a CD transport. 

I used a PCM2704 USB to SPDIF module with Raspberry Pi USB output and Moode. USB to S/PDIF to I2S. 

This sounds better than my regular setup, which is Kali and the I2S DAC. There is significantly reduced CPU noise with the USB to S/PDIF to I2S setup. I am not referring to noise in silence (there is none), but noise modulating on the signal, which creates a slight increase in perceived treble. 

Power for the DIR9001/I2S DAC is separate from the RPi/PCM2704. There is a single supply in the RPi/Kali/I2S DAC. All supplies are the same SMPS.

The difference is unmistakable, and I am having difficulty going back to my regular setup.

Interesting! Was it one of these?

 https://www.amazon.com/Lazmin-Portable-PCM2704-Decoder-Amplifier/dp/B07S2JZXTX/ref=pd_lpo_2?pd_rd_w=G7k5J&content-id=amzn1.sym.116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_p=116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_r=79DGFB9VKCH1JEG7VXA3&pd_rd_wg=cPSl7&pd_rd_r=93b5aa16-0b06-470f-b217-b0996c794240&pd_rd_i=B07S2JZXTX&psc=1

I was interested in the HDMI audio extractor that you last posted to, but that path (to S/PDIF) might need some work in MoOde that I can't do and this looks like it will just plug in.

Thanks,  Skip