The basic unit of measurement for the audio frequency is the hertz (abbreviated Hz). Without getting into too much detail it is essentially a metric unit that expresses the number of cycles per second that a sound wave is vibrating. At 1000 hertz the common measurement becomes kilohertz. Pretty easy to remember because kilo is a common prefix with Greek roots meaning “thousand”. The human ear, on average, is capable of hearing frequencies between 20Hz and 20kHz, which is also fairly easy to remember because it’s just the number 20 twice.
Frequencies are grouped into three main ranges, all of which containing sub-ranges. The lowest audible range in human hearing is referred to as bass, which lies between 20Hz and 140Hz. Above that is the sub-range mid-bass, which contains between 140Hz and 400Hz. I usually remember 140Hz by multiplying 20Hz by two and adding 100, 400Hz because it is just the middle A on a piano rounded down (it actually lies at 440Hz). Above that is midrange, which contains between 400Hz and 2.6kHz. The next sub-range above this is upper-midrange, which contains between 2.6kHz and 5.2kHz. Last, and highest in the human hearing range, is the high end, which contains all frequencies between 5.2kHz and 20kHz. These ranges are all fairly easy to remember also because the midrange ends roughly at 2 and a half, which is half of five, which is roughly where the high end begins.