t p1 p2 p3 p4 ..... (unlimited)
This statement sets the tempo and specifies the accelerations and decelerations for the current section. This is done by converting beats into seconds.
p1 must be zero
p2 initial tempo in beats per minute
p3, p5, p7, ... times in beats (in non-decreasing order)
p4, p6, p8, ... tempi for the referenced beat times
Time and Tempo-for-that-time are given as ordered couples that define points on a "tempo vs time" graph. (The time-axis here is in beats so is not necessarily linear.) The beat-rate of a Section can be thought of as a movement from point to point on that graph: motion between two points of equal height signifies constant tempo, while motion between two points of unequal height will cause an accelarando or ritardando accordingly. The graph can contain discontinuities: two points given equal times but different tempi will cause an immediate tempo change.
Motion between different tempos over non-zero time is inverse linear. That is, an accelerando between two tempos M1 and M2 proceeds by linear interpolation of the single-beat durations from 60/M1 to 60/M2.
The first tempo given must be for beat 0.
A tempo, once assigned, will remain in effect from that time-point unless influenced by a succeeding tempo, i.e. the last specified tempo will be held to the end of the section.
A t statement applies only to the score section in which it appears. Only one t statement is meaningful in a section; it can be placed anywhere within that section. If a score section contains no t statement, then beats are interpreted as seconds (i.e. with an implicit t 0 60 statement).
N.B. If the csound command includes a -t flag, the interpreted tempo of all score t statements will be overridden by the command-line tempo.