Either smacking the palm of the hand onto the mouthpiece, or usign an open embouchure and pure tongue into the mouthpiece. Notated with either x-shaped noteheads, or give the pitch and a verbal instruction (if pitched notes are required). By depressing valves, a range of pitches can be produced.
Multiphonics are achieved by singing into the instrument while playing. Notate sung notes with small noteheads. Easy and effective on the trombone, although it is hard to sing a note lower in pitch than the one being played.
The Orchestra: A User's Manual is a free resource and will remain so. It still receives between 8,000 and 16,000 unique visits per month from all over the world. See the testimonials. Thanks to all the donations, I have been able to create this responsive re-design. But the movies and sound clips recorded in 2004 do show their age. I would really like to re-record everything and add many more techniques, especially for solo and ensemble writing. I estimate this will cost around £30,000. If you know a source of such funds, please contact me: a.hugill [at] bathspa.ac.uk