32 Hz: This is the lowest frequency selection on the EQ. This sits in the lowest of low bass frequencies, where sub information resides in mixes –such as kick drums and bass instruments. Some speaker systems can't even reproduce this frequency.
64 Hz: This second bass frequency starts to become audible on decent speakers or subwoofers. Again, mostly bass drums and bass instruments will reside in this region.
125 Hz: Many small speakers, such as in your laptop, can just about handle this frequency for bass information. In other words, if you turn it up on most systems, you'll hear more bottom in your mix.
250 Hz: This is still considered low-end, but more of the "woofy" sound of bass and drum sounds. Guitars and pianos will have a large amount of low end in this frequency range.
500 Hz: Now were approaching midrange frequencies, but still some of the low end of vocals and the mids of bass instruments sit here in a mix.
1K: This is now low midrange of most instruments such as guitars, pianos, snare drums, etc.
2K: The 2k frequency can boost or cut the "nasal" sound of your music, in the range your voice makes when you hold your nose and talk.
4K: 4k is the upper mid range that many electric guitars sit in, as well as a large portion of many instruments.
8K: This is getting into the high end, where the majority of cymbals and hi-hats are, as well as upper range of synths, pianos and guitars. Many vocals have a lot of information in this range.
16K: Theoretically, us humans can hear just above 20K, so this is true high end. If you crank this up, your mixes will get ‘sizzly'. This is the top of high end on the iTunes equalizer.
A rare find! Fascinating article on how to get the most from different acoustic environments.