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In this installment of the Foundations of Audio series, author Brian Lee White shows producers and audio engineers how to properly apply equalization (EQ) and improve the sound of their mixes. The course covers the use of parametric and graphic EQs—and filters such as the high/low pass filters and shelf filters—in a variety of musical settings. These principles can be applied to any digital audio workstation platform, including Logic and Pro Tools, as well as analog workflows.
We've discussed frequency as the oscillation speed of the soundwave, but what about the other dimension, amplitude? A waveform's amplitude, or amount of push and pull, can be measured using sound pressure level, or SPL. SPL is a logarithmic scale measured in decibels, or dB, above a standard reference level. The standard reference level most commonly used for the starting point of 0 dB is 20 micropascals RMS.
Pascals are unit of measurement for pressure or stress. 20 micropascals is usually considered the threshold of human hearing at 1k. The decibel scale is a logarithmic measurement scale. Turning up an audio signal's volume by 1 dB is basically imperceptible. For most of us, it takes at least a 3 dB increase for us to notice it. However, because of its logarithmic scaling, the loudness escalates quickly.
A 10 dB increase represents a perceived doubling of loudness, and an increase of 20 dB is about four times as loud. Sound confusing? Don't worry. All you need to remember is that 0 dB marks the threshold of our ability to sense sound, and as dBs increase, amplitude increases, and so does the perceived loudness of the soundwave. For example, a quiet room has a noise floor about 20 to 30 dB, while a normal conversation at the dinner table sits it at around 40 to 60 dB.
An average vacuum cleaner is about 80 dB, while front row at a rock concert gets up to around 120 dB. Beyond that, our threshold of physical pain starts at about 130 dB.
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