How to Tell If Your FLAC File Is Real or Fake
You downloaded a FLAC file from an online store like Qobuz or HD Tracks, or perhaps from a shady website. The file extension says .flac, your media player confirms it's lossless, and it takes up way more space than an MP3. So it must be real lossless audio, right?
Not necessarily. A FLAC file is just a container — it perfectly preserves whatever audio was put into it. If someone takes a 128 kbps MP3, decodes it, and re-encodes it as FLAC, you get a file that looks like lossless but sounds like a low-bitrate MP3. The data that was thrown away during lossy compression is gone forever. Re-encoding to FLAC doesn't bring it back.
This happens more often than you'd think. It's been found on peer-to-peer networks, lesser-known download stores, and even on some streaming platforms. The question is: how do you tell the difference?
The answer is in the frequency spectrum
Every audio file has a frequency spectrum — a map of how much energy exists at each frequency, from low bass notes to the highest harmonics your ears can (and can't) hear.
Real lossless audio from a CD or hi-res source uses the full frequency range available to it. A 44.1 kHz file can contain frequencies up to 22,050 Hz (its "Nyquist frequency"). A genuine lossless file will typically have content extending naturally all the way up to that limit.
Lossy codecs like MP3 and AAC save space by cutting off high frequencies — the stuff most people can't hear. A 128 kbps MP3 typically cuts everything above ~16 kHz. A 320 kbps MP3 cuts around 19-20 kHz. When someone transcodes that MP3 back to FLAC, the cutoff stays. The frequencies above the cutoff are just silence, packaged in a bigger file.
That sharp cutoff is the fingerprint of a fake. And spectral analysis is how you find it.
A real-world comparison
I recently compared two FLAC files from my own collection. One I purchased from Qobuz, a store known for sourcing directly from labels. The other I downloaded for free from a band on Bandcamp that listed the track as FLAC.
Here's what SoniqTools found when I analyzed both.
File 1: David Bowie — Space Oddity (Qobuz, 96 kHz / 24-bit FLAC)
Genuine Lossless — Full Spectral Content
The spectrum shows audio content extending to roughly 37 kHz — well beyond the 22 kHz limit of CD audio. In the spectrogram, bright content is clearly visible up to about 25 kHz, while fainter energy — still real signal — extends all the way to 37 kHz before trailing off. This is what genuine hi-res audio looks like: a natural, gradual tapering of energy in the upper frequencies, with harmonics from real instruments visible throughout the range. The 96 kHz sample rate isn't wasted here — there's real content above CD range.
File 2: Stick Men — Time's Insane Ashes (Bandcamp, 44.1 kHz / 16-bit FLAC)
Possible Lossy Transcode — Premature Frequency Cutoff
The difference is clear. Despite being a FLAC file, the spectrum drops off sharply around 19 kHz — a telltale sign of a lossy source, likely a 256-320 kbps MP3 or AAC that was re-encoded to FLAC. A genuine CD-quality recording would have content extending smoothly to the 22 kHz Nyquist limit. Instead, there's a hard wall where the lossy encoder cut things off. The spectrogram makes it unmistakable — you can see exactly where the audio abruptly goes silent.
What to look for
Here's a quick reference for spotting fake lossless files:
- Hard cutoff at ~16 kHz — almost certainly transcoded from a 128 kbps MP3
- Hard cutoff at ~18-19 kHz — likely from a 192-256 kbps lossy source
- Hard cutoff at ~20 kHz — possibly from a 320 kbps MP3 or high-bitrate AAC
- Natural rolloff near 22 kHz — genuine CD-quality lossless (or better)
- Content above 22 kHz — genuine hi-res audio (if the sample rate supports it)
The key word is "hard" cutoff. Real music has a natural, gradual decrease in high-frequency energy. Lossy codecs create an unnatural, abrupt wall. Once you've seen the difference a few times, it becomes obvious.
Why this matters
If you're paying for lossless audio, you should get lossless audio. A fake FLAC file gives you the file size of lossless with the quality of an MP3 — the worst of both worlds. You're wasting storage space on a file that sounds no better than a fraction of its size.
For DJs, it matters even more. Playing a transcoded file through a club sound system will expose the quality loss in ways that headphones might mask. That missing high-frequency sparkle and the subtle compression artifacts become obvious at volume.
And if you're an audiophile who has invested in a quality DAC, a good pair of headphones, or a high-end speaker setup — playing a transcoded file through that chain is a waste. All that careful engineering in your signal path is faithfully reproducing the artifacts of a lossy encode. You deserve to know that the file feeding your equipment is actually delivering what it claims.
How to check your files
Traditionally, the go-to tool for this has been Spek, a desktop application that generates spectrograms. It works well, but requires downloading and installing software.
SoniqTools does the same spectral analysis — plus dynamic range, clipping detection, stereo correlation, and automated quality verdicts — directly in your browser. No download, no installation, no account. Drop a file in, and you'll see its true quality in seconds.
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