Compress an Audio File and Reduce Its Size

Audio file too big for WhatsApp, email or Discord?

A recording made on your phone or a song in WAV quickly goes over upload limits. WhatsApp rejects audio files over 16 MB sent as media, Gmail caps attachments at 25 MB and many other email services at 20 MB (encoding an attachment makes it about a third bigger), and Discord accepts 20 MB on a free account. Pick the target that applies to you: the tool sets the MP3 bitrate by itself based on the length of your audio so it stays just under the limit, and shows the expected size before you start. If your file is already smaller than the limit, it tells you: there's no need to compress it.

Working out audio file size: length and bitrate

An MP3's size depends only on its length and its bitrate, meaning the amount of data used per second: size in MB = bitrate in kbps × length in seconds ÷ 8,000. At 128 kbps, one minute weighs 0.96 MB; at 96 kbps, 0.72 MB; at 64 kbps, 0.48 MB; at 32 kbps, 0.24 MB. Under 16 MB, that gives about 17 minutes at 128 kbps, 33 minutes at 64 kbps and over an hour at 32 kbps. The tool does the math in reverse: for a 45-minute lecture to send on WhatsApp, it picks 40 kbps and gets a file of about 13.5 MB. A CD-quality WAV weighs nearly 10.6 MB per minute: as a 128 kbps MP3, it becomes eleven times smaller.

Voice or music: which bitrate, mono or stereo?

For speech (voice memo, lecture, meeting, interview, podcast), a bitrate of 32 to 64 kbps is enough: the voice stays clear and the file is tiny. In that case, choose mono: the whole bitrate goes to a single channel instead of being split between two. At the same size, the voice is clearer; at the same quality, mono weighs half as much as stereo, which is why the option halves the bitrate in “Quality” mode. For music, keep stereo: 128 kbps is a good balance, 96 kbps is still fine and 64 kbps noticeably muffles the highs. When the target size is very small (under 32 kbps), stereo would sound bad: the tool then switches to mono automatically. MP3 removes information for good: keep your original file, and start from it rather than from an MP3 that's already compressed.

What the tool does, and what it doesn't

“Compress” here means making the file smaller, not adjusting the sound's dynamics: the compressor you find in a studio, on a mic or in Discord, which brings loud and quiet sounds closer together, is a different thing and doesn't change the file size. The tool reads MP3, M4A, AAC, WAV, OGG, Opus, FLAC, WMA, AMR and AIFF, as well as the audio track of a video, and always outputs an MP3, the format everything plays. The title and artist are kept, the album art is removed. To keep only one part, use the “MP3 Cutter” first; to convert without aiming for a size, “Convert Audio to MP3”; for a whole video, “Compress Video”.