Sound intensity, also known as sound pressure level, is a measure of the magnitude of sound. It is typically measured in decibels (dB) and phon (ph). Decibel is a unit of measurement used to quantify the intensity of a sound relative to a reference level. It is a logarithmic scale, meaning that a small change in decibels can represent a large change in sound intensity. Phon is a unit of measurement used to quantify the loudness of a sound relative to a reference level. It is a linear scale, meaning that a small change in phons can represent a small change in sound intensity.