How can you tell if a FLAC is fake?
A fake FLAC is a lossy file, usually an MP3 or AAC, converted to FLAC. It takes up lossless-sized space and says FLAC everywhere, but it sounds exactly like the file it was made from, because converting to FLAC cannot bring back what the MP3 encoder threw away. You can spot it in under a minute: MP3 and AAC encoders cut off the high frequencies at a fixed point, and that flat ceiling survives the conversion. A real CD-quality FLAC carries sound almost all the way to 22 kHz. The same test works on WAV and AIFF files, which get faked the same way.
Check whether a FLAC is really lossless
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Pick a file to testStart with a track you doubt: one from a blog, a forum or a friend's drive, or an album where every file is the same size per minute as an MP3 would be. Test a couple of tracks from the same album, since fakes usually come in whole albums.
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Open it in a spectrogramDrop it on our free in-browser quality checker, which reads FLAC, WAV and AIFF as well as MP3 and never uploads the file. Or open it in Spek, a free spectrogram app, or switch an Audacity track to Spectrogram view.
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Find where the sound stopsLook at the top edge of the coloured area across the whole track. On a genuine 44.1 kHz FLAC the music reaches about 21 to 22 kHz. A flat ceiling well below that is the fingerprint of a lossy encoder.
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Brickwall or gentle fade?An encoder leaves a hard, straight edge with nothing above it. A dark master or a vinyl rip fades out gradually instead. Only the hard edge proves the file was lossy once.
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Read the cutoffA hard edge around 16 kHz means a 128 kbps source. Around 18.5 kHz is about 192 kbps, around 19.2 kHz about 256, and around 19.9 kHz about 320. Above roughly 21 kHz with no edge is genuine lossless.
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Check hi-res claims separatelyA 24-bit 96 kHz FLAC made from a CD copy has nothing above 22 kHz, even though its sample rate allows sound up to 48 kHz. Look for an empty band above 22 kHz in the spectrogram.
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Scan the rest of your libraryIf you found one fake, there are usually more from the same source. Scan your whole library instead of opening files one by one.
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Replace, don't re-encodeGet a genuine copy from a store, a record pool or the CD. Converting a fake FLAC to AIFF or WAV only makes another fake.
What a fake FLAC actually is
FLAC is lossless compression: it shrinks audio without changing a single sample. That guarantee only covers the conversion to FLAC. If the audio was an MP3 before it became a FLAC, every sample of that MP3 is kept perfectly, including the damage the MP3 encoder did. So a fake FLAC is not a bad FLAC. It is a perfect copy of an MP3.
It happens for innocent reasons as often as dishonest ones. Someone converts a folder to FLAC so it plays on a device that wants FLAC, a DJ converts MP3s to AIFF or WAV for an old player, or a download site re-packages MP3s as FLAC to look like a better source. Months later the file sits in your library looking lossless.
The cutoff frequency cheat sheet
MP3 encoders remove the highest frequencies first, and how much they remove depends on the bitrate. These are the cutoffs our analyzer measures on LAME encodes, the encoder behind most MP3s:
- About 16.4 kHz: made from a 128 kbps MP3.
- About 18.5 kHz: made from a 192 kbps MP3.
- About 19.2 kHz: made from a 256 kbps MP3.
- About 19.9 kHz: made from a 320 kbps MP3.
- Content to 21 to 22 kHz, no hard edge: genuine CD-quality lossless.
AAC files, the format Apple Music and many stores use, also cut off at a fixed point, so a FLAC made from an AAC shows the same kind of ceiling. MP3s are covered in more depth in how to spot a fake 320kbps MP3.
Fake hi-res: 24-bit and 96 kHz files
A second kind of fake is a CD-quality file sold or shared as hi-res. Raising a 16-bit 44.1 kHz file to 24-bit 96 kHz makes it more than three times the size and adds nothing. In a spectrogram, a converted file shows music up to about 22 kHz and a dead, empty band from there up to 48 kHz.
Be careful with this test. Plenty of genuine hi-res recordings also have very little above 22 kHz, because the microphones, instruments or mastering simply did not put much there. An empty band is a reason to doubt, not proof. Our checker and Crate Cleaner judge whether a file was ever lossy; they do not try to judge hi-res claims. For DJing, the question rarely matters: a genuine CD-quality file is all a club system needs.
Does a fake FLAC matter for DJing?
It depends on what is underneath. A FLAC made from a 320 kbps MP3 sounds like a 320 kbps MP3, which is fine for almost any gig, and only costs you disk space: around three times what the MP3 needed. A FLAC made from a 128 kbps MP3 is a different story. On a big system the missing top end and the swirly artifacts in hi-hats and reverb tails are audible, and putting it in a lossless container hides that from you when you choose tracks.
Serato DJ Pro plays FLAC, but some older CDJs and standalone players do not, which is why DJs convert to AIFF or WAV. That conversion is safe on a genuine FLAC. On a fake it just moves the problem into another lossless-looking format, so check before you convert. Convert Audio in Crate Cleaner converts FLAC to AIFF, WAV or MP3 and carries your Serato cues across.
Checking a whole library
Opening files one by one works for a single album, not for thousands of tracks. Crate Cleaner’s audio quality check runs the same spectral test on every track in your Serato library, on your Mac, and compares the cutoff with what each file claims. A lossless file with a 320-style cutoff is marked suspect; one made from 256 kbps or lower is marked fake. Files that fade out gently, like dark masters and vinyl rips, get a warning rather than a verdict, and files below 44.1 kHz are never called fake for frequencies they cannot contain. The scan is unlimited on every plan, including free.
From there you can sort your library by what to replace first. Duplicate Finder also uses the result, so when you have two copies of a track it favours the genuine one; see removing duplicate tracks in Serato.
FAQ
Can you fix a fake FLAC? No. The frequencies the MP3 encoder removed are gone, and no conversion can restore them. The only fix is a genuine copy from a store, a record pool or the CD.
Does converting MP3 to FLAC improve quality? No. FLAC keeps the MP3's audio exactly, flaws included. You get a bigger file that sounds the same.
Can WAV and AIFF files be fake too? Yes, the same way. An MP3 converted to WAV or AIFF keeps its MP3 cutoff, and the spectrogram test spots it the same way.
Is a FLAC with a cutoff at 20 kHz fake? Probably made from a 320 kbps MP3 or a high-bitrate AAC, if the edge is hard and flat. A gentle fade around 20 kHz can just be the master, which is why the shape of the edge matters.
Is the online checker private? Yes. It runs in your browser and nothing is uploaded. The file is read and analyzed on your own computer.
Find every fake lossless file at once
Crate Cleaner scans every FLAC, WAV, AIFF and MP3 in your Serato library for lossy cutoffs and ranks what to replace first. The scan is unlimited on the free plan.