6by9 wrote: ↑
Fri Jul 05, 2019 11:49 am
Far too many variables.
The first things to check.
- kernel versions. Only the absolute latest Stretch updates bumped it to the 4.19 kernel, whilst Buster is 4.19.
- Test Buster on a Pi3.
AFAIK The I2S block is identical between the two, although implemented in 28nm instead of 40nm.
The clock setup is different, but the PLLs should still be feeding in the same frequency.
There are differences in the PMIC, so if you're powering your DAC from the Pi then what level of filtering have you applied?
From the Pi's side this is all digital audio, so other than potentially jitter on the I2S clocks there is nothing it can do to change the THD+N figure.
I am not quite sure what is going on but I have tried the latest release of Buster on Pi3B, Pi3B+ and Pi4B, they all have the issue.
I got the last release of stretch before buster came out same thing.
Lastly I downloaded the latest version of Volumio and there are no issues.
In all cases I used the RPI-DAC overlay and just played a 1kHz tone.
Is this because Volumio uses a different kernel?
In all cases DAC backpowers the Pi.