Some other pages on our site you may enjoy:
WASP - Record & display speech signals
WASP is a simple program to record speech signals and to display a spectrogram and pitch track. More information.
ESYNTH - Harmonic analysis/synthesis teaching tool
ESynth is a free program designed to explain the harmonic analysis and synthesis of signals. With ESynth you can create signals by adding together individual sinusoidal waveforms (sinewaves) and study the resulting waveform and spectrum. You can also perform an analysis of an input waveform, to see how a given sound can be represented in terms of a sum of sinewaves. More information.