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A 40 MB recording won’t go through email, and a folder of lectures won’t fit your upload limit. Choose a preset or type the size you need, and each file is re-encoded at the bitrate that gets it there. You see the size before and after, and nothing leaves your computer.
Processing locally on your device
Overview
This tool compresses file size, not dynamic range. (A dynamics compressor evens out loud and quiet passages and does not make files smaller.) For lossy formats, size depends almost entirely on bitrate and duration: megabytes ≈ kbps × seconds ÷ 8,000. A four-minute song is about 9.6 MB at 320 kbps, 3.8 MB at 128 kbps and 1.9 MB at 64 kbps. Because the relationship is that simple, the compressor shows an estimate for every file before you start and can work backwards from a size you type.
There are five presets. High (192 kbps) and Balanced (128 kbps) suit music, Small (96 kbps) is fine for casual listening, Voice (64 kbps, mono) suits podcasts and lectures, and Tiny (32 kbps, mono) is for long speech recordings. Tiny switches to Opus, because at 32 kbps MP3 and plain AAC sound noticeably muffled. Phones use HE-AAC for such low rates, but that encoder isn’t available in the browser, so Opus is the honest choice here. In target-size mode the bitrate is calculated from each file’s length, with a few percent of headroom for container overhead.
Two other settings save a lot of space on speech. Mixing down to mono halves the information the encoder has to describe, which usually lets you halve the bitrate with no audible loss for a single microphone. Lowering the sample rate to 22.05 or 16 kHz removes treble that voices barely use. Very low MP3 bitrates switch to a lower sample rate automatically, because the format needs it. Cover art is dropped by default, since an embedded picture can add 50 KB to 1 MB per file.
Each file is read directly by FFmpeg running in WebAssembly, so long recordings don’t need to be decoded into memory first. The engine downloads once (about 31 MB) and is then cached. If a compressed result would come out larger than the original, for example when you compress an already small 64 kbps file at 128 kbps, the tool keeps the original instead and tells you, so you never end up with a bigger file.
| Bitrate | Size per minute | 4-minute song | Good for |
|---|---|---|---|
| 32 kbps (Opus, mono) | 0.24 MB | 0.96 MB | Speech, voice notes |
| 64 kbps (mono) | 0.48 MB | 1.9 MB | Podcasts, lectures, audiobooks |
| 96 kbps | 0.72 MB | 2.9 MB | Casual music listening |
| 128 kbps | 0.96 MB | 3.8 MB | Everyday music |
| 192 kbps | 1.44 MB | 5.8 MB | High-quality music |
| 320 kbps | 2.4 MB | 9.6 MB | Maximum MP3 quality |
| 1,411 kbps (WAV) | About 10.1 MB | About 40 MB | Uncompressed CD audio |
Drop the audio files you want to shrink, or click to browse. Videos work too.
Choose MP3, M4A (AAC) or Opus as the output codec.
Pick a preset, or switch to Target size and enter the size each file should fit in.
Optionally mix down to mono or lower the sample rate for speech.
Click Compress, compare the before and after sizes, and download.
Use cases
Type 25 MB, or a little less to be safe, into target-size mode and a long interview or rehearsal recording is re-encoded at the bitrate it needs to fit under a 25 MB attachment limit such as Gmail’s.
Use the Voice preset to turn hour-long WAV or high-bitrate MP3 recordings into mono files of roughly 30 MB per hour that still sound clear, ready for a learning platform or podcast host.
The Tiny preset with Opus brings spoken audio down to about 0.25 MB per minute, so long voice messages send quickly over mobile data and take little space on the phone.
Compress background music and narration to 96–128 kbps so pages load faster on mobile, while keeping the same title and artist tags.
Pro tips
Answers to common questions about the audio compressor.
A WAV file shrinks by about 90% at 128 kbps and over 95% with the Voice preset. An existing 320 kbps MP3 drops to about 40% of its size at 128 kbps. Files that are already at a low bitrate can’t shrink much further, and the tool keeps the original if re-encoding wouldn’t help.
The bitrate is calculated from each file’s duration with about 3% headroom, so results usually land just under the target. Opus is variable-bitrate and often comes out a bit smaller. MP3 snaps down to the nearest standard bitrate. If a file is too long to reach the target even at the codec’s minimum bitrate, you’re warned.
Below about 48 kbps, standard AAC and MP3 lose a lot of clarity. Phones use HE-AAC for those rates, but HE-AAC encoding isn’t available in the browser’s encoder. Opus was designed for low bitrates and keeps speech clear at 32 kbps, so it’s the better tool for that job.
No. This tool makes files smaller by lowering the bitrate. A dynamic range compressor is an audio effect that reduces the difference between loud and quiet parts; it changes how the audio sounds, not the file size.
Yes, a little, because it is decoded and re-encoded with a lossy codec. At moderate bitrates the difference is often hard to hear, but it adds up over repeated re-encodes, so keep your original.
No. ToolEnhancer processes files on your own device inside the browser. They are never sent to, stored on or seen by our servers.
Yes. The audio compressor is free to use with no sign-up, no watermarks and no daily limits.