Final answer:
An LFO used to modulate sound through shaping the frequency spectrum is known as filter modulation or filtering, applied to various parameters to alter the character of a sound source.
Step-by-step explanation:
When an LFO (Low Frequency Oscillator) is used in the context of sound design, it modulates various aspects of sound to create variations in the sound's timbre or expression. This modulation can be applied to different parameters such as pitch, amplitude, or filter cutoff. The process is typically referred to as modulation. Specifically, when an LFO is used to control or alter the character of a sound source by shaping the audio signal's frequency spectrum, it is known as filter modulation or simply filtering.
Sound equipment like synthesizers and function generators have controls for both the amplitude, which affects the loudness, and frequency, which affects the pitch of the sound. An oscilloscope might also be used to visualize sound characteristics. In musical terms, instruments are classified by the method by which they produce sound; for instance, a guitar would be classified as a string instrument because its sound is produced by vibrating strings.