Before we get to the finer points of boosting and cutting EQ, it’s important to establish a quantitative reference. (That’s geek-speak for “how much.”) Since our ear doesn’t perceive volume in a linear fashion, we use a logarithmic scale to measure increase and decrease in volume, measured in decibels (dB).
Contrary to popular belief logarithms are not produced by beating sticks on hollowed out tree trunks, but there are musical applications. One dB is considered the least amount of change in sound the human ear can detect without a reference. Certain “golden ears” can hear smaller subdivisions, but for our purposes we’ll stick with one dB as a reference point.
Getting back to the logarithmic scale, while 1dB is the smallest rate of change we can hear, a boost of 3dB is not merely adding by two, it actually results in a doubling of voltage, which equates to sound pressure in audio equipment. As applied to mixing, a small boost or cut will sound more natural. Too much EQ can introduce phase problems, plus the added gain decreases headroom by adding more volume to the overall mix. To hear the effects of a 3dB boost or cut, import a song from a commercial CD into a stereo track in your DAW software. Insert a parametric EQ, select 10kHz with a fairly broad bandwidth (if your plug-in allows it), and cut it by 3dB. Use your EQ plug-in’s bypass to hear the results. Do the same at 8kHz, 6kHz, 3.5kHz, 1kHz, and 250Hz. You should hear a pretty dramatic difference when you compare it the original. Now do the same with 1dB cuts and boosts. In the following tips we’ll discuss where in the frequency spectrum we might wish to boost or cut EQ, and what musical effects this will have.