Very nice work. I enjoyed the subdued energy of this one. Towards the end of the piece at 2:44 I could hear spit flying out of the 'bone. How'd you do that?
That's called a "blat" and almost all brass instruments are capable of producing this sound. You have to drive a particularly low frequency range pretty hard to get this sound with GPO. In real life you produce the sound by quickly and forcefully blowing a lot of air through the instrument, causing its bell to vibrate strongly. When Fr. horn players do it, it is an impressive and majestic sound.