Pages coming from (2004-2013):

Music and New Technologies - Conservatory "A.Casella" in L'Aquila- Italy

Using RTsect

The use of  RTSect is straightforward. Start-up it using the key: 

The upper pane shows the waveform (like an oscilloscope). The lower pane shows the spectrum (like a spectrum analyzer) 

Here the formants were all switched off, so that you can see the waveform as a typical sawtooth, with some amount of Gibbs phenomenon (ringing)  due to the circumstance that the number of partials is limited (finite). The exponential overall shape of the ll peaks is due to the -6 db/octave slope. If also the frequency scale were logarithmic (i.e., notes or pitch, rather that frequencies in Hertz), the shape would be rectilinear. 

Note: LTAS = Long Term Average Spectrum (or  LTS, Long Term Spectrum), namely the spectrum taken over a long period ( > 30 sec). It should typically show the average quality of the signal. 

Try the LTAS blue key, you can see a average spectrum accumulating. The red key reset the spectrum.