In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal). Sample rate is the number of samples of audio carried per second, measured in Hz or kHz (one kHz being 1000 Hz) and is a determination of audio quality. VoIP is typically 8kHz or 16kHz.