>>2954094
An audio frequency PWM signal is differentiated by C7 and R3, and the resulting spikes at the base of Q1 discharge integrator capacitor C6. So the output of U1C is a sawtooth wave whose frequency is determined by the square wave input.

I also want to buffer and offset the square wave to send to the rest of the circuit, which is fairly classical analog synth territory - it has a voltage controlled filter and a voltage controlled amplifier. The output is audio between 50 - 4000 Hz.

But I understand that the square wave from the Pi will contain all these very high frequencies because the rise/fall time is measured in nanoseconds. And I know that interference is more of a problem with high frequencies. My SPI interface however is well separated from all of this audio stuff, in the top right of the board.

Maybe I am just overthinking it. I've heard a lot of stuff about separating signal ground and power ground, but it's not like I'm driving a motor or something