Fake lossless detector: is your FLAC real?

Load an audio file and we analyse its spectrum in your browser to tell whether it is truly lossless or comes from an MP3 (a «fake lossless»).

A free fake-lossless detector: load a FLAC, WAV or MP3 and it measures the frequency cutoff of its spectrum to tell whether the file is genuinely lossless or was transcoded from a lossy MP3. It all runs in your browser — your file is never uploaded.

How it works

Lossy codecs discard the highest frequencies, leaving a sharp cutoff. A real lossless file keeps energy up to near the sample-rate limit. The tool shows the average spectrum and where it drops off — a hint, not a definitive verdict.

The spectrum tells you what the file contains, not whether you can actually hear the difference. For that second question there is the blind ABX test.

Frequently asked questions

How do you detect a fake lossless?

Lossy codecs like MP3 throw away the highest frequencies to save space, leaving a sharp cutoff (often around 16–20 kHz). A genuine lossless file keeps energy up to near the sample-rate limit (~22 kHz at 44.1 kHz). We measure where the spectrum drops off.

Is it 100% reliable?

No. It is a strong hint, not proof. Some music genuinely has little high-frequency content, and some encoders preserve more highs. Treat a low cutoff in a «lossless» file as a red flag to investigate, not a final verdict.

Is my file uploaded?

No. The file is decoded and analysed entirely in your browser with the Web Audio API. Nothing is sent to any server.

What cutoff does each format have?

Roughly: MP3 128 kbps cuts near 16 kHz, 192–256 kbps near 19 kHz, 320 kbps and high AAC near 20 kHz, and true lossless reaches ~21–22 kHz at 44.1 kHz. These are typical values, not absolute rules.