Bass Booster

Small speakers, thin sound, and what a bass boost fixes

Earbuds, phone speakers and laptop drivers are physically small, and small cones move very little air at low pitches. A song that sounds full in a car can feel thin on a desk. In other cases the recording itself is light: a podcast made with a cheap microphone, an acoustic guitar take that lacks body, a beat that was mixed on speakers that exaggerate the bottom end. Raising the low frequencies is the direct way to rebalance those files.

This tool does it with a low-shelf filter. Think of a shelf as a step in the frequency response: everything below the chosen frequency is lifted by the same amount of decibels, and everything above it is left alone. That makes a shelf different from a narrow peak, which would lift a single note region and leave the rest flat. For adding weight to a whole mix, a shelf is the more natural shape, because the kick, the bass line and the low part of a voice all rise together.

You get three knobs. Bass boost runs from 0 to 20 dB and starts at 8. Bass frequency runs from 40 to 250 Hz and starts at 100. Output level runs from minus 12 to plus 6 dB and starts at minus 2. A limiter sits at the end of the chain, and the page shows the peak and loudness of the result so you can see what the boost did.

Choosing the frequency, band by band

The table in the Numbers tab lists the usual names for each part of the low spectrum. The sub-bass region, roughly 20 to 60 Hz, is felt in the chest more than heard, and most phones and small speakers cannot reproduce it at all. Bass proper, from about 60 to 250 Hz, holds kick drums, bass guitar and the foundation of a mix. Above that, the low mids from 250 to 500 Hz add warmth, but too much there turns the sound muddy.

The Bass frequency knob decides where the shelf begins. Set it near 60 or 80 Hz and the boost goes to the deep end, which is the right choice for a big system or good headphones and a poor choice for a phone speaker, where that energy has nowhere to go. Set it near 150 to 250 Hz and you lift the whole body of the mix, which is audible on almost any device but can start to cloud voices and guitars.

A reliable approach is to pick the device you listen on and work backwards. For earbuds or a car, try 100 to 150 Hz. For a phone speaker, try 150 to 200 Hz with a modest gain. For a subwoofer or closed-back headphones, go lower, around 50 to 80 Hz, and let the sub-bass work. The default of 100 Hz sits in the middle and is a decent place to start whatever you own.

The presets, and a way to use the knobs

Four presets give you one-tap starting points: Warm, Punchy, Sub and Earthquake. Warm is the gentle one, meant for adding body to a voice or an acoustic recording without changing the character. Punchy aims at the kick and bass guitar region so that rhythm parts hit harder. Sub moves the emphasis down into the deepest part of the range. Earthquake is the heaviest, and it is meant for tracks that can take it, on speakers that can reproduce it.

Presets only set the knobs, so after tapping one you can still move anything. A good workflow is to tap a preset, then spend a minute on the single knob that matters most. Move the frequency first, because that decides which instruments are affected, and the amount second. Playback restarts within about a quarter of a second after each move, so you can sweep the frequency while the music plays and stop where the kick sounds right.

Keep your own ears honest by comparing often. The Result and Original buttons switch at the same moment of the track, and the space bar plays and pauses. Switch when the boost is at its largest and make sure the Original still sounds like the same song, only fuller, rather than a different mix.

Best settings for common jobs

Hip-hop or electronic tracks that sound flat on earbuds: boost 6 to 9 dB at 90 to 120 Hz. This restores the thump that smaller drivers lose, and it rarely clashes with the vocal.

A voice recording that feels thin: boost 3 to 5 dB at 120 to 180 Hz, and keep it modest. Too much creates a boomy, close-to-the-microphone tone and makes plosives from letters like p and b more obtrusive.

Acoustic guitar or piano: 2 to 4 dB at 150 to 200 Hz, with the Warm preset as a starting point. You want body, not boom.

A workout mix or party playlist on a good speaker: 8 to 12 dB at 60 to 90 Hz, then lower the output level a few dB. The low end uses a lot of energy, and the mix as a whole needs room.

A rule that holds for every job: if you can hear the boost as a separate rumble rather than as extra weight in the music, it is too high or too low in frequency. Back off the gain by two or three dB and move the frequency toward the middle of the range.

Output level, the limiter and distortion

Bass carries a lot of energy. A shelf that lifts everything under 100 Hz by 8 dB raises the strongest, slowest-moving parts of the waveform, and those are exactly the parts most likely to reach full scale and flatten. That is why the Output level knob exists and why it starts at minus 2 dB: it gives the boosted signal a little space before the limiter has to step in.

Watch the peak readout under the waveform. If it sits at or near 0 dBFS, lower the output level a few dB, or reduce the bass boost. A limiter at the end of the chain catches stray peaks, but asking it to hold back large bass peaks can make the kick drum sound squashed and the rest of the mix pump slightly. A cleaner result comes from a lower output level than from a heavy limiter.

The loudness readout in LUFS rises with the boost, which is a reminder that low frequencies add a lot to how strong a track feels. If you plan to put the result next to other tracks, expect it to sit above them after a large boost, and lower the output level to bring it back. Boosting bass is not the same as a general level increase, and the shelf only touches the low end, so the top of the mix stays where it was.

Mistakes and safe listening

The most common mistake is setting the maximum and walking away. A 20 dB shelf at 250 Hz turns most music into a rumble. Treat the gain as a spice: 4 to 8 dB covers most files, and the larger numbers above are for big systems.

The second is boosting low frequencies that the speaker cannot play. If your speakers drop away below 80 Hz, a shelf at 50 Hz simply wastes headroom and can make the cone work hard and distort. Match the frequency to the device.

The third is forgetting what the room does. Bass builds up in corners and near walls, so a mix that sounds right at the desk may boom from the sofa.

Finally, bass is the part of music that tempts people to push their playback level higher, because it feels weak until it is strong. Deep low frequencies are also the hardest to judge by loudness alone. Keep headphones at a level where you could still talk comfortably, and rest your ears regularly, since damage from loud sound builds up quietly and does not announce itself.

File types, quality and saving

Load MP3, WAV, M4A and AAC, OGG and Opus or FLAC, up to 250 MB, so long as your browser can decode it. The tool does not fetch music from streaming sites or links; it processes files that are already on your device, so it is intended for audio you own or are allowed to edit. Most MP4, MOV and WebM videos open as well, which helps with a screen recording whose low end sounds thin; the page reads the sound and the saved result is MP3 or WAV audio.

For saving, pick MP3 at 128, 192, 256 or 320 kbps, or WAV in 16-bit or 24-bit. A size estimate appears before the download. If the track matters, 256 or 320 kbps keeps more detail in the boosted low end. Use WAV if the file is going into a video editor or a music app for further work.

The saved file keeps its original name with the tool name added, so you can always return to the unboosted version. When you finish, the Continue with links under the tool can send the processed result to another effect without a new upload.

Privacy in one paragraph

Decoding, filtering and encoding all take place in the tab you are looking at. No audio is sent over the network, and no copy is kept on a server. The most recent file is kept in this browser's storage on your device so a second tool can offer to pick it up (clearing site data removes it), and the Copy settings link button stores only the knob positions in the address. The drop zone carries a note too: it works with audio files you have, while links from streaming sites cannot be opened.