Spek (IPA: /spɛk/, ‘bacon’ in Dutch) helps to analyse your audio files by showing their spectrogram. Spek is free software available for Unix, Windows and Mac OS X.

Features

Supports all popular lossy and lossless audio file formats thanks to the FFmpeg libraries.
Ultra-fast signal processing, uses multiple threads to further speed up the analysis.
Shows the codec name and the audio signal parameters.
Allows to save the spectrogram as an image file.
Drag-and-drop support; associates with common audio file formats.
Auto-fitting time, frequency and spectral density rulers.
Adjustable spectral density range.