Dissonance/Consonance: Both consonance and dissonance result from the layering of sounds. In a traditional, western sense, harmonies consist of complimentary sounds (the 1st, 3rd and 5th notes in a scale). ccnsonance, by contrast, comprise notes that don’t fit into this pattern of traditional harmony. 20th Century composers, though, like pianist Anton Webern worked to change these perceptions.

Pitch: A sound’s pitch is determined by the rate that the wave vibrates. Combination of these notes can create dissonance or harmony dependent upon the vibrations. The distance between the pitch of two notes is an interval (progression) - an octave is the most common example of.

Duration is characterized but the length of a note or tone. The work of Glenn Branca, in a variety of different ways, utilizes duration to good effect.

Timbre (Tone Quality): The quality of a sound that distinguishes it from other noises (trumpet vs. sax). Timbre relates to the concept of psychoacoustics and how a sound can be pleasant to an individual.

Psychoacoustics: This is the study of how sound affects a listener. It seeks to define what’s pleasant to hear versus what is unpleasant and the results of these experiences on the human body. The layered guitars that make up much of Rhys Chatham’s work is most likely going to be troublesome to most listeners. If his work was rendered in terms of an acoustic guitar, though, a wider audience would be able to sit down and listen.

References:
Connections: Harmonic Series (http://cnx.org/content/m11118/latest/)
Interview w/ Glenn Branca (http://media.hyperreal.org/zines/est/intervs/branca.html)
Psychoacoustics (http://www.appliedmusic.com/psychoCont.html)
Harmony, Dissonance, and Tonality (http://www.essortment.com/all/musicandtheory_rkxl.htm)
Music Theory: Classic Harmony (http://www.aboutmusictheory.com/classic-music-theory.html)