Real 320 kbps MP3s have content up to ~20 kHz. Fakes have a hard cutoff around 16 kHz. Music Library Doctor's FFT analysis catches both — at scale.
The bitrate field in an MP3 is whatever the encoder claimed. A track encoded at 128 kbps and then re-encoded to 320 still reports "320 kbps" in the tag, but the audio has no high-frequency content above ~16 kHz — the original encoder threw it away and re-encoding can't put it back. These fake-320 files are everywhere: forum packs, P2P sites, "free 320 mp3" bundles. Tag-based checkers can't tell them apart from real 320s. Spek is great for inspecting one file at a time, but you'd need a year to check 20,000 tracks manually.
Supported today
Rekordbox · Serato DJ · VirtualDJ (incl. Favorite Folders) on Windows 10+ and macOS (Apple Silicon + Intel). No DJ software? Folder Library mode audits plain music folders too.
FFT-based detection works because lossy compression discards high frequencies — and once they're gone, no amount of re-encoding brings them back. A real 320 kbps MP3 has spectral content all the way up to the Nyquist limit; a fake-320 (re-encoded from 128 or 192) has a sharp cliff right where the lower bitrate stopped. MLD batches this analysis across thousands of files, scores each numerically, and lets you sort your library by actual quality — not by what the tag claims.
An MP3 file whose tag claims 320 kbps but whose audio was up-encoded from a lower-bitrate source (typically 128 or 192 kbps). The file is bigger than necessary, the tag says high-quality, but the audio has the spectral footprint of the original lower-quality source.
Spek is a single-file visual inspector — excellent for one track. MLD runs the same FFT-based analysis but batch-processes your entire library, scores every file numerically, and lets you sort/filter to find the worst offenders.
Yes. A FLAC made from a 128 kbps MP3 source has the same spectrum cliff as the original MP3. The FFT analysis runs on the decoded audio, so the wrapper format doesn't matter — see the fake-FLAC detection guide.
Roughly 100–200 tracks per minute on a modern Mac or PC. A 10,000-track library finishes in roughly an hour. Results are cached, so subsequent scans are instant.
No. Folder Library mode is built for non-DJ users. Just point MLD at any music folder.
Free tier covers scanning and detection. Pro is a one-time lifetime license, or a monthly plan if you prefer. Current pricing is on the homepage.
It finds Rekordbox, Serato and VirtualDJ on its own, and reads plain music folders when you use none of them. Nothing to configure before the first scan.
macOS 10.15+ or Windows 10+. Notarized and code-signed. See pricing
