The wav sample editor is driven from the lisp REPL: you can watch immediately the result of each applied functions. cl-wav-synth comes with some effects as echo, delay, pitch...
The spectrum editor is here just for educational purpose. It show the effect of adding sinus together. But it can load spectrum from the sharc project and can be used to produce instruments sounds (the sample amplitude need to be modified to have a real sound).
The song editor is a way to express a song. A song is just a list of events to write on a wav file. cl-wav-synth traverses the song list and evaluates the form of each song-sample, if the result is a wav sample, it is merged in the song wav file.