# What does the equalizer do?

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As far as I can tell, it makes some sounds louder and others quieter. Can someone explain with a metaphor or visual what it’s doing?

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It makes different frequency ranges louder or softer. For example, small speakers are often not very good at reproducing base ranges, so you might set the lower frequencies to be louder. Or some people have trouble hearing higher frequencies, so you might set them to be louder.

Essentially, there are electronics that can break the sound up in to different frequencies. Each range of frequencies is now it’s own signal which can be manipulated in any way. Equalizers mostly just change the amplitude (volume) of the signals, then combine them all back together into a single signal that is sent to the speaker.

Sound that you hear covers a broad range of frequencies – from 20 hertz (very low, bassy sounds) to 20,000 hertz (very high, shrill sounds).

The equalizer allows you to adjust the volume of the specific frequency ranges independently. So if you feel that your audio system is too shrill, you can lower just the high-frequency volume without also reducing the volume of low or mid-range sounds.

Hi’s, Lo’s, Mid’s all have their own frequency “ranges” – so an equalizer helps you adjust by emphasizing or softening certain aspects of these frequencies

It’s pretty simple, but you need to understand a lot of simple things about sound to get there.

Sound made by pressure waves in something, usually we just think about it as waves in air. Vibrations make sound by squishing together some air (“high pressure”) then pulling apart air (“low pressure”). The vibrations are usually in a pattern we call “periodic”, which is a math term for “something that repeats over and over the same way”. We call how often a sound wave moves from high pressure to low pressure and back to high again its “period”, and the number of times that can happen in one second is the “frequency”. Frequency is measured in a unit called “Hertz”, abbreviated Hz. 1 Hz means “1 time per second”.

So if you strike a tuning fork for the note “Middle C”, it’s a piece of metal that’s been made so it vibrates back and forth exactly 256 times per second. That is the “frequency” of that note. If we recorded it and looked at it in software that visualizes sound waves, we’d see a perfect wave going up and down 256 times per second.

Notes we call “low notes” (bass) have low frequencies compared to notes we call “high notes” (treble).

What if we strike 2 or 3 chords at the same time? That’s when sound gets kind of complicated. You can sort of visualize it by thinking about ripples in water after you drop a rock inside. Those *also* have “high pressure” parts (where the water is tall) and “low pressure” parts (where the water is short).

To oversimplify the math: when two waves meet each other, their pressure is basically added and at that point there is a new wave with the sum as the result. So if you hit 2 tuning forks at the same time, both “high” pressure parts would hit and you’d get a “twice as high” pressure part. Same with the low pressure parts. The result would be the same note, but louder. But that’s if they’re perfectly in line. If you don’t hit them at exactly the same time, some of the “high” parts hit “low” parts and they sort of cancel out, so you get a quieter version of the same note. You tend to see something more like that in water, where the places that the ripples meet look a little chaotic. That’s because it’s hard to make them hit each other perfectly outside of a lab.

ONE MORE THING and I swear I’ll answer the question.

Music has “chords”, where we play more than one note at the same time. When that happens, waves with different frequencies start at the same time and we get a “weirder” wave. Each note’s “high” parts hit the other waves at different intervals and the best way to describe this wave is it’s “wavier”.

So when a song is playing, and there’s like 5 instruments, and they’re all playing different chords, the “wave” for the song looks very chaotic because it’s being made by dozens of different one-note waves and the result is very hard to recognize as “a wave”.

Over the centuries, people who were smart and bored figured out you can use some math to analyze a wave representing a chord and figure out what notes were in it. It’s some pretty complicated math. But if you work it out and know enough about the waves involved, you could separate the whole song into each individual instrument and each note and show the waves for each one.

THAT is where the equalizer comes in. It has some circuitry that can do the math and separate sounds in certain “frequency bands”. That’s just a term that means “any waves with frequencies in a certain range”. If you “turn up” a frequency band, the circuitry separates the waves for that band then raises the high pressures while lowering the low pressures. The result is those notes contribute more to the overall wave and sound louder than the other notes. If you “turn down” the frequency band, it lowers the “high” pressures and raises the “low” pressures which makes those notes seem quieter.

So if you turn all of the low-frequency bands up, that’s a “bass boost”. If you turn them all the way down, the treble parts of the song will seem a lot stronger. So if you know a lot about where certain instruments and notes fall in the frequency bands, you can adjust the frequencies to emphasize certain instruments while downplaying others.

This helps adjust sound output for specific places. The shape of a room, the materials in its walls, and even if it’s empty or crowded can cause echoes and other phenomenon that change the way music sounds. You can use an equalizer to make adjustments to compensate for the room’s acoustics and make it sound like whatever you decide “right” means.

## Really short version without technical info:

Think about how if you have a red light bulb lighting a room, everything looks red. But if you wear specially tinted glasses, they “cancel out” the extra red and you’ll see the colors in the room look more like what they’d look like under white light or sunlight.

Equalizers are like “tinted earplugs” for sound.

A good metaphor might be to think of a piano keyboard: there are 88 keys (typically) with those on the left controlling the longest strings with the lowest notes and those on the right controlling the shortest strings with the highest notes.

In a perfect situation, the piano is constructed to play every string at the same volume. In this perfect situation, the room is acoustically perfect, neither reflecting or absorbing certain notes more or less than any other. The listener in this situation also has perfect hearing, with no difficulty hearing any note. This allows the the performer perfect control over the music and is able to control how vigorously or how gently they play each note.

Alas, real life is rarely perfect. Rooms greatly affect sounds — think of how a large tiled bathroom sounds, or an elevator, or a spacious theater, or a shower stall. None of us have perfect hearing, especially those of us who are older or who listen to earbuds or who have used firearms without hearing protection. Hearing damage occurs unevenly, with some frequencies (some notes) being affected more than others.

Now add to that that when we use recorded music there are several steps that alter the sound. First, the recording changes the sound of the live performance. What microphones are used, how they are placed, what room was used for the recording, and a hundred other factors shape the sound in a certain way. Second, the medium used for playback affects the sound: a vinyl record sounds different than a CD, which sounds different than an MP3. Third, the musical equipment being used for playback affects the sound. Earbuds sound different than electrostatic speakers, which sound different than boomboxes. Every link in the chain changes something.

So there is a long, long list of factors that affect how our recorded piano sounds that make it different than what a live piano in the same room sounds like.

What the equalizer does is try to partially account for all of those changes by making precise changes to each frequency (each note). Maybe it pushes those higher notes up a little so we can hear them more clearly and so they shimmer like the notes from a real piano, and maybe it lowers the bass notes just a little to avoid a hollow boom caused by the placement of the speakers.

Some equalizers are very simple and some are tremendously complex but they all are designed to help shape the overall sonic spectrum to make music sound more lifelike.