Audio files are often much larger than they need to be. A WAV recording takes about 10 MB for every minute, and a podcast saved at 320 kbps is more than twice the size it needs to be for speech. Smaller files send faster, fit email and upload limits, and take less space on a phone.
This compressor reduces the file size, which is a different thing from the "compressor" effect that evens out loud and quiet parts. It re-encodes your audio as an MP3 at the bitrate you pick. You can also turn stereo into mono and lower the sample rate, which helps a lot for speech. Everything happens in your browser, so the file is never uploaded.
Which bitrate to choose
The size of an MP3 is simply its bitrate times its length: one minute at 128 kbps is a little under 1 MB, and at 64 kbps about half that. So the choice is how low you can go before you hear it.
For music, 192 kbps is hard to tell from the original on most speakers, and 128 kbps is fine for background listening. For speech, such as a podcast, a lecture or a voice note, 96 kbps in stereo or 64 kbps in mono sounds clean. Going below 64 kbps makes voices sound thin and watery.
When compressing will not help
Compressing a file that is already a low bitrate MP3 gains little and costs quality, because each round of MP3 encoding throws away a bit more detail. The tool shows the current bitrate of your file; pick a setting clearly below it, or leave the file alone.
WAV and FLAC files gain the most, often 80 to 90 percent, because they store the sound without that kind of compression. Keep the original file if you may want to edit the recording later.
Mono and sample rate
Stereo matters for music. For one voice it stores the same sound twice, so mono gives the encoder twice the bits for the same file size, or the same quality at a lower bitrate.
The sample rate sets the highest pitch the file can hold. 44.1 kHz covers everything people hear. 22.05 kHz keeps voices clear but dulls cymbals and other high sounds, so use it for speech only. To make a video file smaller, use the video compressor.
