The "pitch" of a note is determined by the frequency of vibrations which creates its sound. A high frequency determines a high pitch and vice versa.
The human ear is capable of hearing frequencies in the range of 16 to 20,000 cycles of vibrations per second. Dogs can hear much higher frequencies, and bats even higher frequencies.
The middle A note upon which the entire orchestra tunes its instruments today has 440 vibrations a second, but it was not always so. In the 17th century, the pitch of this same A note was tuned to approximately 374 vibrations per second.
