Link: Understanding the Decibel

In the RF microwave test and measurement world, engineers often deal with the power measurement unit of dBm instead of wattage. However, engineers entering the audio measurement arena will need to understand one more measurement unit known as dBu, which is decibel relative to 1 mW into 600 Ω.

The decibel is a very commonly used yet often misunderstood unit of measurement. The “bel” in “decibel” comes from the name of Alexander Graham Bell. He was interested in the way in which the human ear responds to sound intensity. He used a logarithmic scale to express this sound intensity, in which range from the softest sound to the loudest (threshold of pain) sound is one to a billion (1012) or zero to 12 bels. The decibel is one-tenth of a bel and is abbreviated as dB.

See the full article here: Understanding the decibel :: RadioComms.