I was listening to "Wintermute" for trombone and tape by Bruce Hamilton yesterday. I didn't know anything about the music, other than it was performed by Andrew Glendening. I've performed some trumpet and tape music, so I was prepared for a mix of electronics, musique concrète, samples of standard instruments. Something more abstract, stretching the boundary of normal timbres, since that is the strength of taped accompaniment. I was a little surprised how polished the sounds were, and then it hit me that most of the electronic sounds were not abstractly generated, but were rather samples of electric guitar and electric bass. Oh, and yes some smatterings of drum set, though just hits and ghostly hints of grooves. The timbres were undeniably rock-oriented, and I started listening with a more third-stream/post-rock/indie-classical-to-make-Nico Muhly-wet-himself stance. I could easily see this piece converted to allow a DJ to accompany the trombone, spinning various samples.
There was no four-on-the-floor driving rhythms to make it sound rockish, no blues progressions or pentatonic scales. The only thing evoking the rock genre was the timbre. The electric bass, electric guitar, and drum set sound like rock, especially the overdrive bass sound that was used. What are other timbres that evoke a genre? A particular vibrato in singing can evoke opera, a raspy off-the-string bowing of a violin can evoke "old-timey music." Period instruments are for that very reason, to create the timbres that evoke a time period and genre, thus the use of the shawm, cornetto, harpsichord, and lute. Some world musics have very distinct instruments, like the sitar or the didgeridoo.
Can you name any other timbres that instantly cause you to think of a style of music? Timbres only, no harmonies or melodies, rhythms or tempos.