Our ears and brains help us sense that louder sounds have higher amplitudes and softer sounds have lower amplitudes; however, to put that information to better use in a musical application, we need to be able to measure a sound wave's amplitude more exactly. Then we can create rules of what to do when a specific amplitude level is reached, and control the range of a soundwave's amplitudes to our advantage. This measurement process forms the basis of all dynamics processors. If we can measure it, we can start controlling it.
There are many ways to measure amplitude. Inside our digital audio workstation, we will use dBFS, or Decibels Full Scale. This scale defines our system's maximum and minimum amplitude values, otherwise known as dynamic range. This helps us measure and control the relative amplitude of audio signals within that range. Sometimes the dBFS can confuse people because it counts up from negative numbers and ends at 0. Why does it do this? In a digital audio system, values above 0 are simply cut off, or clipped, creating digital distortion; thus there is no higher value than 0.
The decibel scale is a logarithmic measurement scale. Turning up an audio signal's volume by 1dB is basically imperceptible. For most of us, it takes at least a 3dB increase for us to notice it. However, because of its logarithmic scaling, the loudness escalates quickly. A 10dB increase represents a perceived doubling of loudness, and an increase of 20 dB is about four times as loud. These numbers are helpful to know when mixing a song. Use them as a guide, but let your ears be the ultimate judge.
The listener doesn't care about the dBFS level of your snare drum, just how it feels when mixed with the rest of the instruments in your song. Measuring amplitude using the dBFS is the first step in helping us control an audio signal's dynamic range.
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