Matrix Of Related Frequencies

The chronological hierarchy that underlies most music. Most typically expressible as a binary tree. This is why western rhythmic notation uses terms related by powers of two, i.e. 1/2 notes, 1/4 notes, 1/8 notes, 1/16th notes, etc. This hierarchy continues in the other direction as well: music tends to be organized into measures (bars) of four beats long, and phrases of 4, 8 and 16 bars. This is especially true of most improvised music, where such rigorous "whens" make for more flexible "whats".