DUE-PWM-20Khz-Serial-Control
The PWM 20kHz is only available on pin 6 to pin 9 and user must edits the variant.h before use it.
The location of vatiant.h (windows system) is C:\Users<host_name>\AppData\Local\Arduino15\packages\arduino\hardware\sam\1.6.11\variants\arduino_due_x