EQ Sweep tunes your headphones to your ears.

It's a free Android app. It plays one clean tone at a time, you mark where the sound jumps out or drops away, and it builds the EQ that evens those spots out.

No pair of headphones plays every note equally loud. One spot too loud and cymbals sting or voices turn shouty. One spot too quiet and part of the music goes missing. Most equalizers hand you presets and sliders and leave you guessing which one to move, because music plays everything at once and you can't tell where the problem is. One tone at a time, you can.

A profile for your headphones on your ears, made in a few minutes, with no microphone and no account. EQ Sweep doesn't play your music itself: you take the profile to the EQ you already use, like Wavelet on Android or Equalizer APO on a PC.

Sound passes through several things on its way to you, and each one makes some tones louder and others quieter. Each sheet here is one of them, drawn from bass on the left to treble on the right: where its line rises those tones get louder, where it falls, quieter. Your ear is one of the sheets: the canal is a small tube, and it lifts everything around 3 kHz. The bottom sheet is what you end up hearing, all of them added together. Switch a layer off and the bottom line changes. Press ANOTHER EAR: same headphones, a different result.

So how do you find out what's in your own headphones? Music won't tell you: it plays every tone at once, so you hear that something's off, but not where. One tone at a time will. The needle is the tone you're hearing and the bar is how loud it comes out. The line is that bar for every tone, and a flat line would mean they're all equal. Drag across and listen for where it jumps out and where it drops away. We planted this line in the sound so you can hear it. With your own headphones nothing is drawn: your ear is the only instrument, with no microphone and nobody else's measurements.

Every ear lifts the tones on the way up to about 3 kHz. That climb is normal and it's not what you fix, so "is this one loud?" tells you nothing. Compare instead. Move the tone slowly, back and forth, and ask: is it louder than the tones right next to it? If they rise in step, that's your ear, so leave it. If one stands above both neighbours, it's a peak: mark it and cut it. If it sinks below both, it's a dip: mark it and boost it. PLAY THE THREE plays them one after another, and the bars show what you should hear.

What you're after is a sweep where no tone jumps out. When one does, you tell the app three things: START, where it begins to rise, TOP, where it's loudest, and END, where it's back down. From those marks the app builds a filter, the same shape upside down, so the two cancel out. It starts gently, at 3 dB. Sweep across again, and if the spot still sticks out, cut deeper. You don't need to know what the numbers mean.