You can use a MIDI "program change" message to tell a synthesizer to change to a different sound. The Max object for that is pgmout.
This patch will leap to a random point in the video loaded into jit.qt.movie every 1/4 of a second.
This patch uses a rslider to set the minimum and maximum for random values of the brightness of red ouput by the jit.matrix and the frequency of an cycle~.
This patch will choose a new 1 second segment of a video to play every second.
This patch will play random cosine tones within the range of two octaves above middle C.
This patch will output random MIDI note values stored within the table. The range and offset of values are determined by the top-right random object and drunk object respectively.
The probablility P of something occurring is defined as the number of looked-for outcomes divided by the number of possible outcomes. For example, the probability that heads will show up on an unbiased coin flip is 1 (there is one instance of heads on the coin) divided by 2 (there are two possible outcomes, heads or tails), which means P = 0.5. With this definition, any probability can be described as a number in the range from 0 (impossible) to 1 (absolute certainty).
Above are examples of four types of non-linear contours of values from 0 to 127 that one could use as continuous controller information for a MIDI device.
This program triggers a sound repeatedly, and changes the sound's playback rate with each repetition. The sound file is so short that there's really no need to turn it off with a 0, so we just start it with a 1. The playback rate is calculated so as to cause a random transposition from -12 to +12 equal-tempered semitones, using the twelfth root of 2; the number of semitones (x) of transposition is determined by setting the rate to "2 to the x/12 power". You can put the patch into Presentation mode, which will present a cleaner user interface.
This example shows how to offset the pitch of a midi note by a random amount.