In the Home Recording Studio world we often refer to dB’s. Guitarists will usually tell you to turn them up a couple of dB’s (rarely do they tell you to turn them down!), and mixing advice will often tell you to turn the level down a dB or so at some frequency or other. The term “dB” is frequently used without any real understanding of what it is. In practical terms, turning levels up or down is very easy to do, you just need to push the slider on your Mixer up a couple of notches from where it is, or pull it down a few increments from its setting on the Equalization control. But what are we actually doing; how much is a dB?
A dB (or decibel) can be a relative measurement or it can be an absolute measurement. It was initially devised by those clever guys at Bell Labs to describe the amount of loss that would occur in an an audio signal over a length of cable. So as a relative measurement, it refers to a change in level from where it is, to a different level; it has no dimensions like volts, or current etc. It useful in that if you increase the magnitude of a signal by say 3dB at any level, that change in magnitude will always be the same. In this case, a 3db increase in power will always about double the power. A 3db increase at 1 Watt will increase the power to about 2W; a 3dB increase at 5 Watts will double the power to about 10 Watts and so on. In the negative direction, a 3dB decrease will about halve the power. I have used the term “about” because it’s not an exact ratio due to it’s mathematical derivation. but as far as the human ear is concerned, the differences aren’t noticeable and the error will always be less than 1%.
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