Spectrograms

Spectrogram (F9) opens from the Check menu, from any track, or from a Lossless? report (which already shows a smaller one, with the lowpass found drawn on it). It shows the whole track: time across, frequency up to 22 kHz, and level in dBFS from 0 to -120. Above, a lossless track: the treble fades out naturally and changes with the music.

And a track decoded from an MP3: the treble stops dead at about 16 kHz on every frame. Copy puts the image on the clipboard, and Save image… writes it as a PNG.