An oscillator controls the current sample index of a digital sampler, effectively turning that section of the sample into a wavetable.
Knob 1 – where you are in an odd* 4 minute sample
Knob 2 – frequency multiplier (1 = normal pitch)
Knob 3 – decay
Knob 4 – amount of modulation

As you turn up knob 4 you get more high frequency content. Turning knob 2 down to .5 will lower the pitch by an octave, turning it down to under .006 will get you some really weird results.