Humans have a logarithmic perception of the majority of uncountable and some countable things. A0, which is percieved as the basic note, has a frequency of 27.50 Hz. A1=55 Hz, and A2=110 Hz. You might notice that each time we increase the octave, we multiply the previous frequency by 2. Hence, the formula for the note A would be: An=27.52n Hz If we check this, then A7=27.5128=3520 Hz, which, if you check any sources, you will find is correct.