The tapin~ and tapout~ objects work together to delay sound. The tapin~ creates a place in memory for storing a circular buffer of the most recently received signal. Its argument specifies how many milliseconds of audio it should store. Any connected tapout~ object accesses that memory to get the recent past of an audio signal.
In the groove~ object, you specify the rate of playback of a buffer~ by means of a signal in the left inlet of groove~. Normal playback speed is achieved with a signal value of 1. As shown also in the example "Play a sound file with vibrato", you can create a vibrato by modulating that signal with a low-frequency oscillator.
To impose a vibrato (a periodic fluctuation of frequency) on the playback of a sound file, you can use a low-frequency oscillator (a cycle~ object) to modulate the playback speed of the file. The right inlet of the sfplay~ object controls the playback speed with a rate factor. A value of 1 is normal speed (the default), 2.0 is double speed, 0.5 is half speed, etc. The speed can be supplied as a constant number (float) or with a continuous signal.
This example demonstrates one of MSP's many filter objects—the resonant bandpass filter reson~—and demonstrates how a parameter of that filter—in this case its center frequency—can be easily modulated by a low-frequency control oscillator (cycle~). The range of cycle~ is between 1 and -1, but that range can be amplified by multiplication, and can be offset by addition.
When you want to turn off an oscillator in MSP, you don’t literally stop it or turn it off, you just turn its amplitude to 0; you multiply it by a constant value of 0 so that the resulting signal is 0. Setting an oscillator’s frequency to 0 does not turn the oscillator off, it just stops it dead in its tracks. (It is completing exactly 0 cycles per second, meaning it’s going nowhere.) It will continue to output whatever value it was at when its frequency was turned to 0, which in all likelihood will not be exactly at the value 0.