When we talk about decibels we are really talking about a ratio of two quantities. These quanitites could describe sound pressure, voltage or wattage — all of which are interesting subjects for electronic music composers.

You are probably most familiar with dBs being discussed in terms of SPL (Sound Pressure Level) or acoustic levels. With SPLs we discuss the ratio of an audible sound to the threshold of sound (the point where we can begin to just here a sound). So a loud concert hovers around 115dB above the threshold of hearing which we would call 0 dB. If I were speaking to you my voice would probably sound to you to be about 80dB above the threshold of hearing at 0dB.

But really, the definition of a decibel stems from the unit of measurement called a Bel which is the logarithm of an electrical, acoustic, or other power ratio. Again, it is important to note that a decibel describes the ratio of two powers, not a specific power value. So a dB itself has no absolute value at all.

How do we perceive dBs in terms of Sound Pressure Levels? A sound that is 3 dB higher in level in comparison to another sound may sound just a tiny bit louder. A sound that is 10 dB higher in level sounds to us like it is twice as loud as the softer sound we are comparing it to. If you have ever seen a mixer used for sound reinforcement you may have noticed that the sliders might have dB markings. Try pushing the slider up 10dB while monitoring a sound and see if indeed the sound sounds to you as if it has gotten twice as loud.