A brushless drone motor has three windings (phases) driven by three half-bridges. The ESC does not apply one voltage to one wire and ground to another: it switches the connections around the motor so the stator's magnetic field rotates and the permanent-magnet rotor is dragged along with it.

How fast the field rotates is the commutation. In 6-step drive the ESC energises two phases at a time and advances to the next pair every 60° of electrical angle; the current in each phase is a flat-topped 120° block. In sinusoidal (field-oriented) drive all three phases get smoothly varying currents, which gives less torque ripple and a quieter motor.

The electrical frequency is the pole pairs times the mechanical speed. A 7-pole-pair motor spinning at 20 000 rpm has an electrical frequency of about 2 300 Hz, and six commutations per electrical revolution, so the whine you hear tracks RPM.

Where the beeps come from. An ESC has no buzzer. To make the startup tones it leaves commutation behind and switches the same three half-bridges at an audible frequency with no rotor feedback. The current through the windings exerts a force that vibrates the stator and bell, so the motor itself is the speaker. Because it is open-loop, the rotor does not turn. It just buzzes at the drive frequency.