Two independent dials on the same signal. One sets how much power gets delivered. The other sets whether the switching is invisible or an audible whine.
Pulse-width modulation controls a motor, an LED, or a heater by switching a signal on and off very quickly rather than holding it at some intermediate voltage. Every PWM signal is described by two numbers: a duty cycle (what fraction of each cycle the signal spends HIGH) and a frequency(how many complete on/off cycles happen per second). It's tempting to think of these as one combined "PWM setting," but they control genuinely different things, and mixing them up is a common source of motor whine, flickering LEDs, and overheating drivers that otherwise look "correctly configured."