Arduino PWM Tutorial #1 - How To Change PWM Frequency
The Arduino has a fixed PWM frequency of 490Hz - or does it? On digital pins 3, 9, 10 and 11 it's 490Hz, but on pins 5 and 6 it's 976Hz. Confused?
And it is possible to change the PWM frequency to a higher (or lower) frequency by altering the timer prescalers. Here's how it's done."