Step 7: Putting it all together
How do you get that noise source to come into the composition at 33 seconds? How do you turn on that chiming bell at 16 seconds, then turn it off, then turn it on again at 42 seconds? One way is to use a behavioral voltage source to make the desired sound then turn it on and off by multiplying the sound generating voltage by another voltage that turns the sound on and off, as was done in bell_drum_cymbal_string.asc. You can do the same sort of thing to fade sounds in and out.
The idea here is to set up repeating sounds then use additional source(s) to add those sounds to your composition at desired times by multiplying their voltages by the sound voltages. You can include as many voltages in the final sound output as you want, just keep multiplying them (same as logical "and") together. By starting the sounds up all at once they will remain in perfect sync throughout the composition so they will never be early or late in the time of the music.
Look at composition_1.asc. There are two bells, one in each channel. The pulse_bell voltages operate throughout the simulation but the sounds only show up in the output when V(bell_r) and V(bell_l) are not equal to 0.