Have you ever tried Amiga Module Tracker or PC Scream tracker?
These programs make sound by sending out digitized sample
at diffenrent pitch ( i.e. Digital -> Analogue Convert )
Trakers are different essencially from FM synth (such as ROL,CMF),
because it produces sounds of real world.
GTS has the same function,but there is some differences.
* First,you can input your own music graphically.
this idea is mainly from Macintosh programs
such as Super studio session,Finale,Delux Music.
Well,I'm much inspired by "Super studio session".
and many of samples are from it.
* Second,the music itself is seperated from samples.
Above modules have musical sequence and samples all in 1 file,
and therefore have big size.
But If you have some samples statically,
your music can be created more easily with very small size
(like scream tracker STS).
* Third,GTS can manage .VOC as sample.
You can record your own voice (sampling), -- Analogue -> Digital
and produce music from that sample. -- Digital -> Analogue