The video was very helpful in understanding why the board needs to be redesigned. This is what I ended up with:
I’ve changed the pads for the ESP32 and amplifier board to SMD pads. Continuous ground plane at the bottom, ground pour at the top. Power is routed at the top and there are no signal lines at the bottom. I’ve added a bunch of vias to connect the ground pours at the top to the bottom ground plane. I’ve also moved the GND line in the connector to be close to the I2S signal lines. I’ve updated the board settings with the help of this thread: Board setup - design rules for Pcbway and other questions. I’m unsure how many vias to place. I placed them close to ground pads and in islands.
I think I got everything. Feedback is greatly appreciated.
The other board I’m working on:
(it’s upside down; don’t ask)
It connects to the first board. I know I also have a problem with the cable I’m using to connect the boards. I’ve put the GND cable close to the high frequency I2S signal cables, but the cables really should be shielded. I’m still trying to figure out how to solve that.