Volume booster for audio and MP3 files
I built this so you can make a quiet voice note, recording or song louder without installing anything. Choose a file, set the gain, listen to a preview and save the result.
or drop it here
Level:
The limiter is on by default. It turns the volume down smoothly just before a peak that would go over 0 dB, so boosted audio does not distort. Switch it off and those peaks are cut flat (clipped) instead.
The preview plays at the gain you set. Turn your device volume down first, because +20 dB is much louder.
How it works, and what stays on your device
Your browser decodes the file and I multiply every sample by the gain you choose, from -20 dB to +20 dB. The page shows the gain in dB and as a percent of the original level: 0 dB is 100 percent, +6 dB is about 200 percent, +20 dB is 1000 percent and -20 dB is 10 percent.
Boosting pushes the loudest peaks towards 0 dB, the highest level a digital file can hold. Past that, a sample cannot be stored as it is, and I never let it wrap around into a loud crackle: every sample is held between full negative and full positive. What happens at that limit depends on the limiter, and the page tells you before you save.
With the limiter on, which is the default, I look about 5 milliseconds ahead and turn the volume down smoothly just before a peak that would go over 0 dB, then bring it back up. Every channel is turned down together, so the stereo picture stays put, and the peak lands at or below 0 dB. If the loudest peak stays under 0 dB at your gain, the limiter does nothing and the file is only multiplied. With the limiter off, anything over 0 dB is clipped, which means cut flat at the limit, and that can sound harsh. After you save, the page says whether the limiter acted and by how much, or how many samples were clipped.
A WAV file is saved as WAV and an MP3 as MP3. Files in other formats, such as M4A, OGG or FLAC, are saved as MP3 by default, because MP3 and WAV are the two formats I can write in the browser. You can switch between the two before saving. MP3 is written at 192 kbps unless you pick another quality, the output is 44.1 kHz, and in an MP3 files with more than two channels are mixed down to stereo.
The preview plays the result with the settings you have chosen, so turn your device volume down first.
Nothing is uploaded. The page never sends your audio anywhere, there is no account, and closing the tab clears the file from memory. The file can be up to 200 MB.
Need only part of a file? Cut it down first. Open the audio trimmer
MP3 encoding uses LAME through lamejs, both under the LGPL. Read the licence
Frequently asked questions
How do I make an MP3 louder without uploading it?
Choose the file, set the gain with the slider and press Boost and save. Decoding, boosting and encoding all happen in your browser, so the audio never leaves your device.
Will boosting the volume make it distort?
Not with the limiter on. It keeps every peak at or below 0 dB by turning the volume down briefly around the loud parts, so the rest of the file keeps its boost. If you switch it off, peaks over 0 dB are clipped and can sound distorted.
What do the dB and the percent mean?
Both describe the same change. dB is the usual unit for volume, and the percent shows how much each sample is multiplied: 100 percent is the original, 200 percent is double the sample values and 50 percent is half. +6 dB is about double.
Can the saved MP3 still clip in my player?
The limiter keeps the samples I send to the encoder at or below 0 dB. MP3 compression changes the sound slightly, so a player can occasionally show a peak a little over 0 dB. Save as WAV if that matters.
Does the new file keep the title, artist and cover art?
No. I process the sound only, so the new file has no tags. Add them in your player or a tag editor afterwards.