ABSTRACT
When talking about sound that exists in the air and is heard by our ears (or picked up by a
microphone), volume level is referred to as sound pressure level, or SPL. Our ears respond
to changing air pressure, which in turn deflects our eardrums, sending the perception of
sound to our brains. The standard unit of measurement for SPL is the decibel, abbreviated
dB. The “B” refers to Alexander Graham Bell (18471922), and the unit of measure is actually the Bel. But one Bel is too large for most audio applications, so one-tenth of a Bel,
or one decibel, became the common unit we use today.
