Volume Booster (Audio & Video)
Turn quiet recordings up — or loud ones down — without clipping.
Levels of the original
Volume change
+6.0 dBBefore and after
Solid colour: the sound after the change. See-through band on top: the original. Dashed lines: the ceiling. The preview loops up to 15 seconds and switches between the two in place, so you can compare them.
Save
About the Volume Booster (Audio & Video)
Make a quiet recording, podcast, song or video louder — or a loud one quieter — by anything from −20 to +20 dB. A limiter stops the peaks from clipping, so a big boost does not crackle or distort, and the page measures the file first and tells you how much room there is and how much the limiter will have to work.
Play the before and after preview of any part of the file and switch between the two while it plays. Audio files stay in their format (MP3 stays MP3, WAV stays WAV, FLAC stays FLAC) or can be saved as MP3, M4A, WAV or FLAC. For videos (MP4, MOV, MKV, WebM) only the sound is re-encoded: the picture is copied packet for packet, so it loses nothing and stays in sync. Everything happens in your browser; nothing is uploaded.
How to use it
- Choose an audio or video file. The page reads it and measures its peak and loudness.
- Set the gain with the slider, the quick buttons or the exact field — or press Use … (loudest without limiting) for the most you can add with no limiting at all.
- Leave Prevent clipping with a limiter on; read the forecast of how much it will do.
- Press Play preview and switch between Original and Adjusted; move Preview from to check another part.
- Press Make it louder (or quieter) and download the result.
Examples
Peak −14.2 dBFS · loudness −31.0 LUFS
Room before the ceiling: +13.2 dB. At +12 dB nothing is limited and the loudness becomes about −19 LUFS; the picture is copied unchanged.
Peak −0.3 dBFS · gain +4 dB
The peaks would reach +3.7 dBFS, so the limiter turns them down by up to 4.7 dB (−0.3 + 4 − (−1)); the result never goes above −1 dBFS.
Gain −6 dB
About half the amplitude (×0.501; exactly half is −6.02 dB); nothing needs limiting.
Common uses
- Lecture, interview and voice-memo recordings that are too quiet to hear on a phone.
- Phone and camera videos whose sound is faint compared with other clips.
- Podcasts and audiobooks before uploading, or a song that is quieter than the rest of a playlist.
- Turning down a file that is uncomfortably loud.
How the gain and the limiter work
A gain of G dB multiplies every sample by 10^(G/20): +6 dB doubles the amplitude, +20 dB multiplies it by ten. On its own that would push loud peaks past full scale (0 dBFS), where they are cut off and crackle. The limiter looks 1.5 ms ahead, sees each peak coming and turns the level down smoothly just enough for it to stay at the ceiling, then lets the level recover over about a tenth of a second. It is built so that no sample can go past the ceiling, and its short delay is compensated so the sound stays in sync with the picture. The preview runs the exact same processing on the excerpt you hear.
Reading the levels
Peak is the highest sample, in dB below full scale (dBFS). Loudness is the integrated loudness of ITU-R BS.1770 in LUFS: frequency-weighted like the ear and gated so that pauses do not count — what broadcasters and streaming services use to compare loudness. Room before the ceiling is how far the file can be turned up before its highest peak reaches the ceiling (rounded down to 0.1 dB); with the limiter off it is the room before clipping at full scale. For reference, EBU R 128 sets −23 LUFS for broadcast; much music is mastered far louder. A gain changes the loudness by the same number of decibels, minus a little where the limiter works.
How much to boost
As a rule of thumb, +10 dB sounds roughly twice as loud and +3 dB is a small but clear step. Speech recorded far from the microphone often needs +10 to +15 dB; finished music usually has little room, so any boost is mostly limiting. Keep the forecast in mind: limiting a small share of brief peaks is inaudible, but when the limiter works most of the time (more than about 9 dB of reduction), the sound becomes flat and squashed — choose less gain. The ceiling of −1 dBFS leaves room for the small overshoots that MP3 and AAC encoding and playback can add; EBU R 128 caps true peaks at −1 dBTP for the same reason.
What is kept
Tags and cover art are carried over. Lossy sound (MP3, AAC, Opus) is re-encoded with the original bitrate (or the next standard step up) as its target, so it keeps its quality — AAC and Opus encoders spend fewer bits on very simple sound; lossless sound (WAV, FLAC) stays lossless at the same bit depth. Videos keep their sound codec where the browser can write it, and the uncompressed (PCM) sound of camera MOV and MKV files stays uncompressed. All audio tracks of a video get the same change. Browsers cannot write a few formats, so AIFF becomes WAV, Apple Lossless becomes FLAC, Vorbis becomes Opus, and AC-3, E-AC-3 or DTS sound becomes AAC; the page says so before you start.
Limitations
- Lossy sound is re-encoded once: at the original bitrate the difference is very hard to hear, but it is not bit-for-bit the same.
- Background noise and hiss get louder along with the voice, and distortion that is already in the recording cannot be removed.
- Subtitle tracks and chapters of a video are not carried over.
- Very large videos need a lot of memory: in Chrome or Edge on a computer, turn on “Save straight to a file”.
- Copy-protected (DRM) files cannot be read. One file at a time.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot. The audio engine (and, when the file needs them, the MP3, AAC or FLAC encoder) downloads from MySmartCoPilot the first time you open a file. Your audio and video are never uploaded.
Frequently asked questions
How do I make a video louder?
Choose the video, set a gain such as +6 dB, check the preview and press Make it louder. You get the same kind of file (MP4 stays MP4) with the picture copied unchanged and only the sound re-encoded.
Will boosting the volume distort the sound?
Not with the limiter on: no peak goes past the ceiling, so there is no clipping. What you can hear with very large boosts is the limiting itself — loud passages lose some punch. The forecast tells you how much the limiter will do; if it is a lot, choose less gain.
Does the video lose quality?
No. The video stream is copied packet for packet, exactly as it was. Only the sound is decoded, changed and encoded again.
What is the maximum boost?
+20 dB, ten times the amplitude. Room before the ceiling shows how much you can add before any limiting is needed; beyond that the limiter holds the peaks down.
Why is my file saved in a different format?
Browsers can read some formats they cannot write. AIFF is saved as WAV, Apple Lossless as FLAC, Vorbis as Opus and AC-3 or DTS sound as AAC; you can also choose MP3, M4A, WAV or FLAC under Save as.
Is my file uploaded?
No. The file is read, measured and processed by this page in your browser and never leaves your device.