Lossless Audio Checker
Verify if your FLAC, WAV, or AIFF files are genuine lossless or transcoded. Runs on your device — files never uploaded.
Drop audio file here or click to browse
FLAC, WAV, AIFF, MP3, M4A · processed on your device
How to Check for Lossless Audio
- 1 Upload a FLAC, WAV, AIFF, MP3, or M4A file
- 2 Read the spectrogram — look for a sharp horizontal cutoff where color abruptly drops to black
- 3 Check the verdict and cutoff frequency against the reference table below
How to Read Your Spectrogram
A spectrogram shows every frequency in your audio over time. The horizontal axis is time (left to right), the vertical axis is frequency (low at the bottom, high at the top), and brightness indicates energy.
What does a genuine lossless file look like?
A true lossless recording fills the entire spectrogram from bottom to top. You'll see color and texture all the way up to the Nyquist frequency (half the sample rate — 22.05 kHz for 44.1 kHz files). The energy naturally fades toward the top because most music has less high-frequency content, but there's no abrupt cutoff — just a gradual, uneven fade.
What does a transcoded file look like?
A file that was converted from MP3/AAC to FLAC/WAV shows a sharp horizontal line where all content abruptly disappears. Above the cutoff: solid black. Below it: normal audio content. This "shelf" is the signature of lossy compression — the encoder discarded frequencies above that point, and re-encoding to a lossless format can't bring them back. The tool draws a red dashed line at the detected cutoff.
Frequency cutoff reference table
Different bitrates cut at characteristic frequencies. If the detected cutoff matches one of these, the file was almost certainly transcoded from that source:
| Cutoff | Likely Source | What It Means |
|---|---|---|
| < 16.5 kHz | 128 kbps MP3 | Definitely transcoded — significant quality loss |
| 16.5 – 19 kHz | 192 kbps MP3 | Transcoded — moderate quality loss |
| 19 – 20.5 kHz | 320 kbps MP3 / 256 AAC | Transcoded — minor quality loss, harder to detect |
| > 20.5 kHz | True lossless | No artificial cutoff detected — genuine lossless |
What about the confidence percentage?
Confidence measures how sharp the cutoff is. A lossy encoder creates a "brickwall" — a near-vertical drop where energy disappears within a very narrow frequency range. A sharp brickwall (high confidence) is almost always a transcode. A gradual rolloff (low confidence) could be natural — some recordings, especially older ones or acoustic music, naturally have less high-frequency content. When confidence is low, use the spectrogram as the final proof: look for a clean horizontal line versus a fuzzy, uneven fade.
