GS is for "Geyer Studio" - this is a studio-optimized mouthpiece for your Geyer type horn.  What makes this a studio mouthpiece are its outstanding smoothness and malleability while retaining good slots for accuracy.  Used by Allen Fogle on major Hollywood soundtracks!

The cup is medium deep and paired with an open backbore to create a velvety sound.  The backbore has been carefully optimized to let you find notes comfortably yet open enough to let the pitch slide in the transition between notes rather than just notching in.

In a concert hall, depending on the horn, this can be an incredibly good mouthpiece - particularly on some of the more-recent Geyer-family horns. It won’t work for every player and setup but when it works it works.