Yamaha's Sweet Tenor Sax is incredibly realistic and Boo Hargis said that it sounds so realistic that he would have a great deal of difficulty listening and determining if it was real or not.
There are lots of other instruments on the newer model Yamaha arranger keyboards that are equally as realistic sounding, and in the hands of a good player, they can really make a huge difference in the production of a song.
I personally believe that fingering technique and in depth knowledge of the instrument you are trying to emulate is the key to success. Don Mason was a sheer genius with his guitar emulation, and my son, whom is an accomplished guitarist said it would be impossible to know those sounds were coming from an arranger keyboard.
Jimmy McKinney (JimSax) who was inducted in the Musicians Hall Of Fame in Maryland for his sax playing said he wishes he could get his tenor sax to sound as good as the one on his Tyros2 arranger keyboard.
Attached are a few examples: 4 different sax demos from my PSR-S950.
Sax Demos Gary
