The most important tool you can have in your arsenal is the audio equalizer. Equalizing your tracks so that they fit together in a professional sounding mix is an art form. But it's easy to get to grasp with the seemingly tricky aspect of equalizing.
Whether you are using a parametric equlizer to sculpt your 24 track mix together or a graphic equalizer to tune a concert sound system there are a few general guidelines you can follow to make equalization easier.

There are three different ways of treating the EQ spectrum. You can either filter a frequency out completely, cut an unflattering frequency range out or enhance a specific frequency that flatters the sound you are equalizing.
The parametric equalizer is the most popular and widely used audio equalizer. A parametric equalizer allows you to both filter, cut and boost any frequency range. In addition to that, it also allows you to define the width of the cut, allowing you surgical precision in your cuts or broad and flattering boosts.
The graphic equalizer can be a lifesaver when you need to tweak specific frequencies in a live sound situation. Whether you are trying to equalize a sound system or trying to get rid of feedback when monitor mixing, the graphic equalizer is a great friend to have.
EQ is used on everything. Making thin sounds thicker, boxy sounds better and generally bringing out the best of a specific instrument. Being able to recognize frequencies is something that comes with experience but you can speed up the process by taking frequency recognition tests to further develop your hearing skills.
Equalizing the low end is an important factor considering the tightness of your mix. You need a perfect blend of highs and lows in order for your track to have a professional sound.
Cutting out unneeded low end from instruments that don't have anything of interest in the bass frequencies is a great way to clean up unnecessary clutter in your mix.
Use a high pass filter to filter out expendable low frequencies from vocals, guitars and drums. Leave the bass to the bass instruments such as the kick drum and bass guitar.
Is your mix suffering from a distinct lack of clarity?
Do your instruments sound like they were all drenched in mud before they were recorded?
Get rid of a boomy and muddy mix with some good EQ'ing in the right spots.
Some sounds can have a boxy character. Percussion instruments such as the kick drum can have a cardboard box quality that takes the punch and fullness out of the drum and just makes it sound horrible.
Luckily, with the clever use of equalization you can cut out those pesky cardboard frequencies from your drums and obtain a professional drum sound.
Vocals, for me, are the most important part of any song or production. If a vocal doesn't sound good it can take away from the overall feel of the song.
An ill-defined and nasally vocal sound can make an amazing performance sound lackluster.
So although you should concentrate on getting the best vocal sound in the recording phase, a little bit of EQ while mixing can take a vocal sound to a whole new level.
Ahh...that high end sounds sweet. The angelic soprano voices,
the cymbal washes and amazing sounding orchestral strings. We can lift
up many elements that suffer from lack of high end by adding some high
frequency equalization. Add some air to your tracks with a high
shelving boost at 12Khz or higher. It can give a subtle boost of life
to your instruments.
The best way to familiarize yourself with the different frequency areas of the audio equalizer is to sweep around the frequency spectrum and listen to how each frequency sounds.
Are you looking for a specific frequency to make your guitar sound a specific way? Use my guitar frequency guide to sort through the various frequency areas characteristic to the guitar.
I wrote a very informative tutorial on recognizing frequencies for Audiotuts+ that is worth a look. I recommend it to everyone who wants to further understand the frequency spectrum and how the different areas sound in relation to each other.
For a one-stop, all-you-need-to-know course on EQ, check out Understanding EQ by HomeStudioCorner here.
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