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.
• Translated into 19 languages.

spek.cc
github.com/alexkay/spek

References:

en.wikipedia.org/wiki/Spectrum_analyzer