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’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.
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