This may be a bit overkill, but Baudline is an incredible real-time FFT spectrogram. It's not in Ubuntu repos, so you will need to download it on your own. It displays a real-time analysis of source signal, but it also allows to analyze pre-recorded data. The brightness of a point represent the power of the sound at this frequency, where horizontal axis represents frequencies, and vertical time - so it kind of shows history of your signal.

It's extensive features make it definitely the most advanced spectrogram available for Linux. It may be a bit too complicated for your uses, though. I am not sure what exactly you are looking for.