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).
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 detection and viewing. Lifetime access is $49 — $19 for the first 100 DJs.
