Voice changing combines several audio processing techniques. Pitch shifting moves the fundamental frequency and harmonics up or down. Formant shifting changes the resonant characteristics of the vocal tract independently of pitch, which is what makes a voice sound male, female, or alien. Modulation effects like ring modulation and vocoding multiply the voice signal with a carrier wave to produce robotic or synthetic textures. Layering these effects and adjusting their parameters creates a wide palette of character voices.