Musical Synthesis 101
1.3 The Meter (Amplitude)
Amplitude is a measurement of the intensity of a sound at a point in time. Typically amplitude is measured in decibel units or dB. When measuring the amplitude of a signal in the real world (acoustic signals), we typically measure from 0 dB SPL (decibel sound pressure level aka acoustic pressure) to +infinity dB SPL. But when measuring digital signals, the measurement is taken from -infinity dBFS (decibels relative to full scale) to 0 dBFS. Decibels are best used to represent relativity between amplitudes, therefore when the context of the measurement changes so can the scale.
You’ll notice that two different measurements exist to define the amplitude of signals based on whether they are acoustic/analog signals. In fact there are many different ways to measure a variety of signals, and each one works in a slightly different way. While the contents of this reading are mostly DAW and synthesizer related, we will only be focusing on dBFS for digital audio, but do know that other decibel scales exist and may be used for different reasons.
One way to accurately read the decibel count on an audio signal is by using an integrated decibel meter. There exists a wide variety of meters that all look slightly different, but they all fundamentally work in the same way. Firstly, there will be some indicator of what the decibel level is currently being measured at. Secondly, there will likely be some indicator of the true peak decibel level. The true peak level is important because it can help indicate how dynamic your signal is. Furthermore, you can use the peak level to determine whether your signal is clipping or not. Typically, there will be some colored indicator to help you identify if the signal is clipping.
The way that humans perceive signals is different from the way that computers do. Take a listen to these two sounds and note which one appears to be louder.
If you said the first audio was louder, you’d be wrong. The peak value of the second audio exceeds that of the first. This is why it is important to use other types of units in order to determine how loud humans will perceive an audio signal.
There exists two main forms of integrated readings known as LUFS and RMS. Both of which measure the average audio level over time. RMS gives us a reading of the average level of an audio signal in relation to its power output, while LUFS, the standard, gives us a reading of how loud a signal is over time based on human perception of loudness. This is what makes LUFS the ideal unit to use when assessing the loudness of a track.