A FLAC made from a 128 kbps MP3 source plays back as "lossless" in any player but has the same spectrum cliff as the original MP3. MLD scores them accurately.
FLAC is a container — it's lossless compression, but only relative to whatever audio was put into it. A FLAC made from a 128 kbps MP3 source contains exactly the audio the original 128 kbps MP3 contained, no more. Plex, Roon, Navidrome, and Apple Music all happily display these files with lossless indicators because the container is lossless. The actual audio is anything but. These fake-FLACs sneak into audiophile libraries through deceptive uploads, free pack sites, and bulk archive grabs.
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Rekordbox · Serato DJ · VirtualDJ (incl. Favorite Folders) on Windows 10+ and macOS (Apple Silicon + Intel).
Lossless container indicators (the green "FLAC" badge in Roon, Plex's lossless tag) reflect file format only, not signal quality. The only way to verify a FLAC is genuinely lossless is to decode the audio and inspect the spectrum. A real lossless rip has full-spectrum content out to the Nyquist limit; a fake FLAC made from a 128 kbps MP3 has a hard cliff around 16 kHz that the FLAC wrapper can't hide. MLD's FFT pipeline runs that check on every FLAC in your library in one pass.
Sometimes it's deceptive uploading — a torrent labeled as a lossless rip when it was actually made from a lossy source. Sometimes it's people trying to "upgrade" their MP3 library by transcoding to FLAC, not realizing the audio quality doesn't improve. Either way, the resulting files take up many times the disk space of the source without any audio benefit.
Essentially yes — and that's the problem. The audio inside is whatever the source was. The FLAC wrapper just stores it without further loss. If your audiophile setup is filtering for lossless format, fake FLACs slip through and crowd out genuine masters.
Yes. Any lossless container can hold lossy audio. MLD decodes the audio and scores it regardless of the wrapper format — ALAC, WAV, AIFF, FLAC all get the same FFT-based score.
0–100. Real lossless rips usually score 90–100. Fake FLACs from lossy sources score 30–55 with the FAKE marker. Borderline files score 60–80 and get a "likely lossy source" warning so you can decide manually.
No direct integration — MLD operates on the file system. You clean up the files, your media server rescans, and the library updates. No plugin to install, no auth dance.
Free tier covers detection and viewing. Lifetime access is $49 — $19 for the first 100 DJs.
