MP3 Preview is a free VST3/AU plugin for Macs with Apple silicon (M1 and later). It uses a real MP3 encoder and decoder in real time, at any bitrate from 32 to 320 kbps or VBR, so you can hear a track or mix as an MP3.
Recent Updates
2026 November
- MP3 Preview 1.0.0: Initial release.
To use MP3 Preview, put it on a track in a DAW. The track is encoded to MP3 and decoded again as it plays, so what you hear is what the file would sound like at that bitrate and those settings.
For more flexibility, I included a mix control, which then goes to a 2nd control that blends in the Difference signal that was originally taken out, until only the Difference is left at 100%. You can listen to this by soloing the Difference, and it's more pronounced at lower bitrates.
Bitrate: Bitrate of the MP3. 32 to 320 kbps are constant bitrate. V0 to V9 are VBR, where the encoder varies the bitrate frame by frame, V0 the highest quality. 320 is the default.
MP3 Mix: Blend between the original audio and the MP3.
Difference Mix: Blend between the MP3 mix and what the encode removes. At 320 kbps the difference is faint. At low bitrates it is a sound of its own.
Solo MP3: Plays only the MP3.
Solo Difference: Plays only what the encode removes from the signal.
Lowpass: Applies a filter for the bitrate (20.5 kHz at 320 kbps, lower at lower bitrates), as encoders do by default.
Joint Stereo: Encodes the two channels together where that uses fewer bits, as encoders do by default.
Bypass: Passes the original audio through unchanged, delayed by the same amount as the MP3 so the track stays in time.
Drag a slider's number to change it in small steps, click it to type a value, or double-click it to reset it. Click MP3 Preview for the menu: Reset, Dark or Light Mode, Hide Info View, Window Size, and sanguine.works, which reads Update Available when there is a newer version.
An MP3 encoder works in frames and holds a few back, so the plugin has a fixed delay, from about 95 ms at 320 kbps to about 300 ms at the lowest bitrates and VBR. It reports the delay to the host, so with plugin delay compensation the track stays aligned. Changing the bitrate, Lowpass, or Joint Stereo restarts the encoder, with a brief gap while it refills. Sessions above 48 kHz are resampled to 48 kHz (44.1 kHz for 88.2 and 176.4) for the encode and back again, as a bounce to MP3 is.
Requires macOS 11 or higher on Apple silicon. VST3 and AU. Encodes with LAME (libmp3lame, LGPL) and decodes with minimp3.