ProvenanceModerate signal
Codec artefacts
Traces left by lossy encoders such as MP3, AAC and Opus.
Lossy codecs discard information the encoder's psychoacoustic model believes is inaudible. What remains carries traces: a bandwidth ceiling, quantisation patterns in the frequency domain, pre-echo around sharp transients, and joint-stereo behaviour in the upper bands.
For detection purposes codec artefacts are mostly a nuisance, because they overwrite the fine detail several features depend on. But identifying them is valuable in itself: knowing a file has been re-encoded tells you how much to trust the rest of the reading.
How this tool uses it
Encoding evidence is used to modulate the weight of spectral features and to lower confidence, not to raise or lower the probability directly.
What else produces the same reading
- Multiple generations of re-encoding compound each other.
- Transcoding a lossy file to WAV hides the file extension but not the artefacts.