A difference of x Hz produces a beat at 30x BPM. So notes at 440Hz and 443Hz (a difference of 11.8 cents) would produce a 90BPM tempo. But at higher frequencie

A difference of x Hz produces a beat at 30x BPM. So notes at 440Hz and 443Hz (a difference of 11.8 cents) would produce a 90BPM tempo. But at higher frequencies the same increase in Hz corresponds to a smaller number of cents: 4400Hz to 4403Hz would be 1.18 cents.