Find out whether a FLAC, WAV or AIFF file is really lossless or was made from an MP3 or AAC. The checker analyses the whole file, looks for the frequency cutoff lossy encoders leave behind and gives a plain-language verdict with a spectrogram you can save. Your music never leaves your computer.
Drop your FLAC, WAV or AIFF files on the box, or click Choose audio files. You can add a whole album at once.
Wait a moment while each file is decoded at its native sample rate and scanned from start to end.
Read the verdict: Lossless, Suspicious, Fake or Inconclusive, with the highest frequency found and an explanation.
Check the spectrogram: a flat, dark area above a hard horizontal line (often at 16, 19 or 20 kHz) means the file came from a lossy source.
Download the spectrum image or the CSV of all results to keep a record or show a seller.
Typical lossy cutoffs at a glance
Lossy encoders cut the highest frequencies first, because they are the hardest to hear and the most expensive to encode. The position of that brick-wall edge on a spectrogram is a good clue to the source. These are typical values; encoder version, settings and the music itself move them a little.
Where the spectrum stops
Likely source
Verdict here
Below 11.5 kHz
64 kbps MP3 or less, low-quality streams
Fake
About 15 to 16 kHz
96 to 128 kbps MP3 (many encoders), 128 kbps AAC
Fake
About 17 kHz
128 kbps MP3 from LAME
Fake
About 17.5 to 19 kHz
160 to 192 kbps MP3, VBR V2 to V4
Suspicious
About 19 to 20 kHz
192 to 256 kbps MP3, VBR V0
Suspicious
About 20.5 kHz
320 kbps MP3 (LAME)
Suspicious
21 to 22.05 kHz, or up to the top
Genuine 44.1 kHz audio (the edge is the recording's anti-aliasing filter)
Lossless
22 to 26 kHz in an 88.2/96/192 kHz file
CD-quality audio upsampled to a hi-res rate
Fake (hi-res)
How to read the spectrogram
Time runs left to right, frequency bottom to top. Bright colours are loud, dark purple is silence. The scale is linear, so the top quarter shows the treble where lossy cutoffs appear.
A hard horizontal line with flat darkness above it across the whole song is the classic lossy fingerprint. The checker draws a green line where it found it.
A soft, uneven fade that changes with the music is natural. Cymbals and breath noises reaching the top now and then are a good sign.
Thin bright lines at fixed high frequencies (for example 15.7 or 19 kHz) are usually electrical noise or a pilot tone from a broadcast or tape, not a lossy encoder.
Tips for reliable results
Check several tracks from the same album: a whole release with the same 16 kHz edge is much stronger evidence than one quiet track.
Bright, loud music shows cutoffs most clearly. Solo piano, speech or old mono recordings may be Inconclusive.
A genuine file can still be badly mastered: clipping and loudness are mastering choices, not signs of lossy encoding.
To look closer, open the file in the Audio Spectrogram Generator and zoom into the top band, or test whether you can actually hear a difference with the ABX Audio Test.
Frequently asked questions
How can a FLAC file be fake?
FLAC is lossless only in the sense that it stores exactly what it is given. If someone decodes an MP3 or AAC file and saves the result as FLAC, the file gets bigger but the detail the lossy encoder threw away is gone for good. Such files are often called fake, upscaled or transcoded FLACs.
How does the checker detect a transcode?
To save bits, MP3, AAC and Vorbis encoders apply a steep low-pass filter and remove almost everything above a fixed frequency. The checker measures the average spectrum of the loud passages in 50 Hz bands, looks for a sudden drop of 20 dB or more with an empty band above it, and compares its position with typical encoder cutoffs.
Which cutoff matches which bitrate?
Typical values: about 16 kHz for 128 kbps MP3 with many encoders (around 17 kHz with LAME), 17.5 to 19 kHz for 160 to 192 kbps or VBR V2, about 19 to 20 kHz for 256 kbps or V0, and about 20.5 kHz for LAME at 320 kbps. Genuine CD audio usually continues to around 21 to 22 kHz. The exact figure depends on the encoder and its settings.
Can a genuine lossless file look fake?
Sometimes. Old analogue recordings, quiet acoustic music, some masters that were low-passed on purpose and files made from tape or vinyl may have little treble. These usually fade out gradually, which the checker reports as genuine. A sharp edge between 17 and 20.7 kHz is marked Suspicious rather than Fake for this reason; compare with other tracks from the same release.
Can it detect fake 24-bit or hi-res files?
Yes. If a 24-bit file only contains 16-bit values with the extra bits set to zero, it is flagged as padded. If a 96 or 192 kHz file has no content above about 22 to 26 kHz, it was almost certainly upsampled from 44.1 or 48 kHz audio and is not real high resolution.
Which formats can I check?
FLAC, WAV (including 24-bit, 32-bit float and RF64) and AIFF work in all modern browsers. ALAC in M4A works in Safari and usually in Chrome. MP3, AAC and Ogg files are accepted too, but they are lossy by definition, so the checker simply reports their cutoff. APE, WavPack and DSD are not supported by browsers; convert them to FLAC first.
Are my files uploaded?
No. Each file is decoded with your browser's Web Audio API and analysed with JavaScript on your own device. Nothing is sent to a server, so you can check large collections privately.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.