630 is the middle of the 20Hz to 20kHz audible range... but the FFT only goes up to 8176 so a large portion of your display would be unused if you made 20kHz the top of the display. The middle of a 64Hz to 8176Hz range is 723Hz.
Maybe he has hardware capable of sampling at 44kHz.
Where did you get 43Hz steps? 64 to 8167 in 64 steps is 7.872784%