Because the bitrate field is a tag, not a measurement. Files re-encoded from low-bitrate sources keep their 320 tag forever — but not their high frequencies.
You bought (or downloaded, or were sent) an MP3 tagged 320 kbps. You play it on good speakers or headphones and it sounds dull, smeared, or thin. The bitrate field says high quality, your ears say otherwise. That's a fake-320: a file that was once a lower-bitrate MP3 (typically 128 or 192) and got re-encoded to 320 along the way. The tag updated, the audio didn't. The file is bigger than necessary but contains no more information than the source.
Supported today
Rekordbox · Serato DJ · VirtualDJ (incl. Favorite Folders) on Windows 10+ and macOS (Apple Silicon + Intel).
The bitrate field in an MP3 is metadata, not a measurement of audio quality. Once a lossy encoder discards high frequencies, no amount of re-encoding restores them. MLD's FFT analysis reads the actual spectrum and scores the audio honestly — if the high-frequency content is missing, the file scores low regardless of what the tag claims. That's how you turn "this sounds wrong" into a sortable, numerical answer across your whole library.
Really worse. The high frequencies that give MP3s their air and clarity are physically absent in a fake-320 — they were thrown away by the original lower-bitrate encoder and re-encoding can't recreate them. On accurate playback gear the difference is audible.
No. Lost frequencies can't be reconstructed from what's left. The only fix is to obtain a genuinely higher-quality source — Smart Upgrade searches for one and lets you swap.
Be skeptical of any 320 MP3 from forum packs, free-download sites, or unknown sources. Files from official stores (Beatport, Bandcamp, iTunes Plus, Tidal/Apple Music ripped lossless) are reliable. MLD's score after the fact catches whatever slipped in.
Streaming sources downloaded for offline use are usually genuinely high quality — Apple Music Lossless, Tidal HiFi, Spotify Premium are all real lossless or near-lossless. The fake-320 problem is mostly with files distributed outside legitimate stores.
Yes — see the fake FLAC detection guide. The FFT analysis runs on decoded audio, so the wrapper doesn't matter.
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