Spectral ceiling
The frequency above which a recording contains essentially no energy.
Many generative models are trained on band-limited representations, so their output simply stops at a particular frequency, often with a sharp shelf rather than the gradual roll-off of a microphone recording. Seen on a spectrogram it is a horizontal line with nothing above it.
This used to be one of the most cited AI-audio giveaways. It is far less useful than its reputation suggests, because every lossy codec produces the same shape. A 128 kbps MP3 of a live orchestra also has a hard ceiling near 16 kHz.
The honest position: a hard ceiling on a verifiably lossless file is meaningful evidence. A hard ceiling on a file of unknown provenance is close to worthless.
How this tool uses it
Detected and reported, but automatically down-weighted whenever other evidence indicates lossy encoding. It can never carry a result alone.
What else produces the same reading
- MP3, AAC and Opus encoding at any moderate bitrate.
- Old or low-quality source recordings.
- Deliberate low-pass filtering as a production choice.
Questions
No. It is the single most common false-positive cue in circulation. Lossy compression produces the same shape, and most audio on the internet has been compressed at least once.