We have mentioned how the the human ear's audible frequencies go from 20 Hz to 20 KHz. Let's now try and label these frequencies to get a better idea of where they belong in the audible spectrum.
Table 2.2. The frequency spectrum
Extension (octave extension)
1 Hz - 20 Hz
They are not audible by the human ear. They are generated by earthquakes for example, or by large reed organs in churches.
Very low frequencies
20 Hz - 40 Hz
It is the lowest octave audible to the human ear. The bass drum in a drum kit and the low notes on a piano as well as the sound of thunder or air conditioning are within this range.
40 Hz - 160 Hz
Almost all low frequencies in music are within this range.
160 Hz - 315 Hz
The Central (C) note on the piano (261 Hz) is within this range. This range contains many of the sound signal informations that can be potentially altered by poor equalizing.
315 Hz - 2.5 KHz
The ear's sensitivity is at its highest in this range. This band's sound quality, if taken individually, is similar to that of telephones.
2.5 KHz - 5KHz
In this range the isophonic curve
[Isophonic curves - Equal loudness contours
has its highest peak and is therefore the range the ear is most sensitive to. To equalize an instrument in this range increases its presence in the mix, bringing it in front of the other sounds (this is true if you want to obtain the opposite too: if you want to hide an out of tune voice you've been forced to keep in your mix because the singer is the record label's boss' friend's cat's son-in-law, remove the frequencies at 3 KHz and drown it in reverb... it'll become a distant, almost metaphysical presence!).
5 KHz - 10 KHz
It is the range in which we perceive the brightness of sounds because it contains many of the harmonics generated by the notes belonging to the previous ranges. The acoustic energy levels are very low here and the consonants 's', 't' and 'c' belong to this range.
Very high frequencies
10 KHz - 20KHz
Even less acoustic energy is found in this range. Only the highest harmonics of certain instruments are here. They are nevertheless important because they confer the indispensable brightess, without which the mix would become dull.