Total Harmonic Distortion (THD) is defined as the ratio of the signal power at the fundamental frequency to the signal power of all other harmonics observed at the switch output (VD) with a pure sinusoidal waveform applied to the switch input (VS). This specification influences switch selection in audio applications where the fidelity of the signal is altered as it is channeled through the switch. RON and RON Flatness are the switch characteristics that have the largest influence on THD and noise performance.