What everyone should know about Equalizing and Compression

Equalizing and Compression are the two easiest ways to adjust a sound system to work for a situation.

We listen to music in a lot of different situations: alone or together, talking, dancing or lying around, when our roommates are sleeping, when we can make all the noise in the world, etc.
By adjusting the frequency response and dynamic range of the music, we can make it work best for these different situations.

Equalizers let you set how the music competes with other sounds

An equalizer will have a set of controls that goes from low to high. Different equalizers have different numbers of controls.
If you have an EQ with two knobs, one for bass and one for treble, then you can add mid by turning them both down, and remove the mid by turning them both up.
If you have an EQ with three knobs, the middle one will be mid, and the bottom and top ones are bass and treble, respectively.
The more frequency controls an EQ has, the more narrow the range of each control is, so you may want to adjust a few at a time so they form kind of a pretty slope, for the most natural sound. If you want it to sound natural.
"Loudness" is the relationship of the mid frequencies with the whole thing. Boosting the treble and bass while reducing mid makes a song sound louder, while reducing the bass and treble while boosting the mid reduces "loudness."

An equalizer splits the sound into a set of ranges from high to low, and then lets you adjust the volume of each range.

EQ adjustments often make the whole thing sound louder or quieter, so you often have to adjust the volume at the same time.
EQs allow you to change which frequency range dominates the sound, because when you cut one frequency, you can afford to make the whole thing louder, and you hear more of the rest. So if you have a song with a bad bassline, you can take the focus away and let the lyrics take over by boosting the mid and cutting the bass, or just cutting the bass and boosting the volume.

Compression and limiting let you change the music's dynamic range

Here's how to understand dynamic range and all this stuff: take the example of trying to watch an action movie quietly enough not to wake up your roommate, but loud enough to catch the whispered dialog between action scenes. The action scenes are so much louder than the dialog that you have to keep adjusting the volume. You turn it down when it gets to a certain point, and turn it back up again when it's quietened down and doesn't seem like it's going to get louder again. That "certain point" is the threshold of a compressor. The amount that you turn in down is the ratio. And the "attack" and "release" or "speed" of the compressor is the speed of your response in changing the volume, and how long you wait before deciding it's quietened down and you can turn it up again. The dynamic range is the difference in volume between the loud and quiet parts. Older movies had a narrower dynamic range, which was more convenient but less realistic. Music has gone the other way - recordings used to have quiet quiet parts and loud loud parts, but now our quiet parts and loud parts are at about the same volume, because of compression.
A limiter is a compressor without controls. You can adjust the dynamic range by adjusting the volume going into the limiter. The louder the volume going in, the more narrow the dynamic range coming out. You'll have to adjust volume before and after the limiter in opposite directions to keep the actual volume level.
When you reduce the dynamic range of a piece of music, it becomes clearer and sounds louder, which often means you get to turn it up.

Adjusting for your situation

• If you're listening to music alone and want to hear it clearly, reduce loudness and open up the dynamic range. You do that by cutting bass and treble, boosting mid, and reducing compression ratio.
• If you've got some conversation going on, cut the mid so that the music leaves room in the middle for the voices in the room.
• When the party gets started, and you want it to sound loud as hell without having it loud as hell, and you want people to be able to talk instead of shouting, you'll need to louden up the mix and reduce dynamic range. With the medium frequencies out of the way, people can hear each-other's voices through the loud bass and treble, which are making the music sound loud. A narrowed dynamic range makes the music sound more artificial, so everyone's brains can separate it more easily from the conversation, and increases clarity of musical detail, so the music becomes easier to understand, as if it's being enunciated better. That means people can spend less energy keeping track of both the music and conversation, and they don't end up escalating the volume by raising their voices.
• If you're trying to keep the neighbours happy late at night, cut the bass as much as possible, and reduce dynamic range as much as possible. Bass cuts through walls more than anything else, so that's usually what neighbours hear. And a mix without dynamic range sounds more and more like a drone the further away you go, so to the neighbours it may just sound like a fan or something.

Handy party tricks

• Another way to make things sound louder is to distort the whole thing a little bit, if you know how. Then you can turn it down without making it sound turned down.
• Reducing volume is hard when you don't want to affect the vibes of a party room. The only thing you can do is make adjustments between songs. Increase loudness, decrease volume, and let the next song come on. Err on the side of reducing volume too much, and then let yourself bring it back up again during the beginning of the next song.
• Whatever you can do to make each song come in at around the same volume, do it.