Is the following correct: The frequencyData is a 32 element array. The audio range from 20Hz to 20,000Hz is divided into 32 smaller ranges and each range is assigned to an index. If this is correct, what are the ranges for the 1st four indexes?
At that range, the bins are 12.5Hz apart.
The first is 37.5Hz (not 20Hz), then 50Hz, then 2 bins each for 62.5+75, 87.5+100.
If you hit it with 50.1Hz, it would predominantly fall into the 50Hz bin. If you measured 43.75Hz, it would probably split between the 37.5Hz bin and the 50Hz bin.