06 - Loudness

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In sound and music production we make a distinction between amplitude and loudness. Measuring the amplitude as a number between 0 and 1 is very handy from a digital signal processing perspective, but it says very little about how we perceive the loudness of a sound. This perception is very subjective, and it depends on several factors: how long the sound lasts, its frequency, as well as its amplitude. We are a lot more sensitive to higher frequency sounds than we are to lower frequencies. In order for us to perceive a very low tone as the same level as a high tone, the low tone needs a lot more energy than the high tone, as you can see in this plot:

We will not go too deeply into the distinction between amplitude and loudness, but it is useful to know that there is a difference, especially when you compare a commercial pop track (LOUD!!! but still not exceeding 1.0) and your own mixes, which will not be very loud.