What are the most important frequencies in a mix?

Whether in a studio recording, mixing, mastering, or performing live every engineer needs to know the answer to this question.  

In general, the frequency spectrum can be broken up into three sections, the bass, mid-range and highs or treble. Each area has an impact on the other and one adjustment can affect all the frequencies in the spectrum. 

Bass is the most difficult range to work with. Improper treatment here can negatively affect all frequencies that follow. Bass frequencies can reduce headroom, muddy up the mid-range, and reduce clarity in the high frequencies. This frequency range is mishandled the most. 

Mid-range contains frequencies of most instruments and vocals present in any mix. Even bass and kick drum have frequencies in the mid-range. Cymbals and other various high-pitched instruments can also have a presence in the mid-range. A weak mid-range can reduce the impact of a musical composition greatly. 

High frequencies or treble. This is where high-pitched instruments like cymbals cannot have competition. One thing people liked about analog was the saturation created when you hit the tape hard. This process creates harmonics and or distortion that can give a recording clarity, punch and that airy feeling, partially with the vocals. Bass and min-range frequencies can produce harmonics that if not treated will wash out your high frequency content. Ever notice how some recordings conceal the cymbals? Lack of low pass filtering is generally why. 

So what is the most important frequency in a mix? It is the mid-range. Bass adds warmth, bottom and beef and centers a mix. The highs add clarity, height and space to a mix. Without these elements, a mix will sound anemic and flat but the mid-range gives the sound its character its presents, power and it is where most of the emotional content lies. 

Understanding frequencies is essential to good sound. Ear training is required as part of an engineers training when learning about frequencies. Everyone in the music business should have some understanding and training with frequencies. Next time you hear a band or recording that sounds muddy, cannot hear the vocals, some instruments are louder than others, and some things you cannot hear at all, now you know why. It is all about the frequencies.