Why "lossless" files can be fake
Converting an MP3 to FLAC gives you a file that is lossless from that point on, but the detail the MP3 threw away is gone for good. These upscaled files turn up in downloads, sample packs and DJ pools, and they're big, labelled lossless, and sound like the MP3 they came from.
The giveaway is the treble. To save space, MP3 and AAC encoders remove high frequencies above a cutoff that depends on the bitrate. Real CD-quality audio usually has content, even if only faint noise, right up near 20 kHz; an upscaled MP3 has a hard ceiling below that.
How the check works
WAVR averages the spectrum across up to 240 slices of the track (skipping silence), smooths it, and takes the 2–8 kHz range as a reference level. It then finds the highest frequency still within 45 dB of that reference, and measures how steeply the level falls just above it.
| What WAVR finds | Verdict | Typical source |
|---|---|---|
| Sharp drop (>25 dB) below 16.5 kHz | Likely lossy | MP3 at 128 kbps or lower |
| Sharp drop between 16.5 and 19.8 kHz | Possibly lossy | MP3 or AAC around 192–256 kbps |
| Content up to about 20 kHz or a gentle roll-off | No lossy cutoff found | Genuine lossless, or a very high-bitrate source |
The honest limits
- It's a heuristic, not proof. A clean result doesn't guarantee the file is genuine; 320 kbps MP3s can keep content close to 20 kHz.
- Some real recordings are dark on purpose: old tapes, lo-fi mixes, speech, or masters with a low-pass filter. These can be flagged.
- Files at 32 kHz or lower can't contain high frequencies in the first place, so the check is skipped.
For a second opinion, press S in the panel to open the spectrogram. A fake usually shows a flat, straight ceiling across the whole track. Full walkthrough: How to tell if a FLAC is fake.
Fake FLAC questions
How accurate is this?
It is a heuristic. It is good at catching files made from 128 to 256 kbps MP3s, which cut off sharply below 20 kHz. It can be fooled by very high-bitrate sources, and it can flag genuine recordings that are dull or were low-passed on purpose.
Can it check MP3s?
It will show where an MP3's content stops, which hints at the bitrate it was encoded at, but an MP3 is lossy by definition, so the verdict is mainly useful for files that claim to be lossless.
I found a fake. Can WAVR fix it?
No tool can bring back what the MP3 removed. If file size matters, convert the fake back to a good MP3 or M4A and save the space.
Does it upload my files?
No. The analysis runs in a background thread in your browser.