Need to get 20kHz PWM on pin D9.
I've spent an hour reading through pages like "secretOfArduinoPWM", "PwmFrequency", "TimerPWNCheatsheet", About all I could get was that something called TCCR1B affects the timer1 which operates pin 9. This is WAY over my head. I've seen different examples, but I don't even know which of them to start with.