Had the same problem with Spek on THIS POST
But I found a much more advanced Spectrum Anaylser which can display (Spectrogram, Melodic Range Spectrogram, Peak Frequency Spectrogram, waveforms and so on)
It also plays files too and very customisable!!
Read my post here to find out more: In Tools run a shortcut
Sonic Visualiser website here: http://www.sonicvisualiser.org/screenshots.html