Audio equalizer.

From left to right: 31 and 62 Hz are the sub-bass and the thump of a kick, felt more than heard and missing on phone and laptop speakers. 125 and 250 Hz are the body of bass, guitar and voice, and where a mix turns muddy or boomy. 500 Hz and 1 kHz are the middle of most instruments; too much sounds boxy or honky. 2 and 4 kHz are presence, where the ear is most sensitive: a little makes a voice clear, a lot makes it harsh. 8 and 16 kHz are cymbals, breath and the sizzle of an S. Play the song, then drag one dot up as far as it goes and sweep it left and right: the part of the sound that jumps out is that band.

Bass lifts the bottom three octaves; Treble lifts the top three. Smile raises both ends and dips the middle, the V-shaped curve that sounds fuller at low volume because the ear hears less of the extremes when it is quiet. Vocals cuts the low end a little and lifts 500 Hz to 4 kHz, which brings a singer forward. Voice is for speech, a podcast, a lecture, a phone recording: it cuts 31 and 62 Hz hard, where rumble, wind and handling noise sit, and adds presence for clarity. Every preset is a starting point; drag any dot from there.

Cutting usually sounds more natural. If a song sounds thin, try lowering 500 Hz to 2 kHz before raising the bass; if a voice is muddy, cut 250 Hz before boosting 4 kHz. Boosts also need room above the loudest peak, and a finished song has almost none, so a limiter catches the peaks here and keeps them under −1 dB. That keeps the file from clipping, but a big boost on a loud master makes the limiter work hard and the hits lose some punch. Switch to Original and back at the same moment to hear whether a change really helps.

Each band is a peaking filter one octave wide (Q 1.41), centered on the standard ten-band frequencies, adjustable in steps of 1 dB from −12 to +12. The curve on screen is calculated from the same coefficients the download is filtered with, so where two raised bands overlap the curve shows their sum. The preview plays through the browser's own peaking filters, which use the same formula, and a limiter set like the download's, so what you hear is what you save.

No. It changes an audio file, so the EQ travels with it to wherever it is played. To change everything a device plays, use the equalizer in the player or the system: Spotify has one under Settings, Playback, Equalizer; the Apple Music app has one under Settings on iPhone and in the Window menu on a Mac; Windows needs a system-wide EQ such as the free Equalizer APO.

Anything your browser can play: MP3, WAV, M4A and AAC, FLAC, OGG Vorbis and Opus in current Chrome, Edge and Firefox. The download is an MP3 at 128, 192 or 320 kbps, or a 16-bit, 44.1 kHz WAV, the same length as the original. We set no length limit; the whole file is held uncompressed while you work, about 20 MB a minute in stereo, so an hour is fine on a laptop.

An equalizer changes the sound; the bars in a music visualizer only measure it. The faint shape that moves behind the curve here is that measurement, a spectrum of what is playing, bass on the left and treble on the right, so you can see a boost land. The guide on equalizers goes through both, and the audio visualizer turns the spectrum into a video of your song.

No. The file is decoded, filtered and encoded on your device, and the download is made there. The page only counts that a file was saved, with the format and the preset, never a name or the audio.