Audio Recording with Equalizers – 10 Equalizer Modes – Part Ten – Shelf EQThe Shelf EQ is a vital tool in the art of recording, mixing, and mastering music. It is called a Shelf EQ because it does not taper off at the ends, but remains constant like a shelf until the end of the spectrum. If you use a high Shelf EQ that begins at 10kHz, it will continue in a curve until it reaches a certain point and then remains at that level as far as the upper Frequencies continue. If you are working at a sample rate of 44.1kHz, then the high shelf EQ will continue all the way to 22,050Hz, and a low Shelf EQ will continue all the way to a theoretical 0Hz.
In actuality, it takes roughly 10Hz to reach the edge of a digital wave file, and approximately +/-10dB, but this is practically irrelevant to any audible recording. The Shelf EQ will sound and mostly appear perfectly straight beyond its edge, curve, or slope. A Shelf EQ will normally have Fixed Frequency positions to choose from along with +/- Gain options. As an example, you may have a Program Equalizer with 30Hz, 50Hz, and 100Hz Shelf EQ positions with boost and cut Gain, and you may have high Shelf with 6kHz, 8kHz, 10kHz, 12kHz along with boost and cut Gain. All of these options will extend all the way to the extreme high or low spectrum beyond the starting curve or slope, but the Frequency that is designated will mark the position that the EQ goes from flat to adjusted. In some ways, you could look at a Shelf EQ as being a Bell-Shaped EQ where only one side of the EQ has the Bell, and the other side continues at the height of the Bell. Shelf EQ is not always the exact same slope or curve.
There are some rare cases where a “Q” control that would be used in Band mode, doubles as an adjustable edge for the Shelf EQ as well. In this case, the user is able to not only select the Frequency from which the Shelf will begin processing, but also the shape of the edge Frequency that makes the transition from flat to Shelf. In this case, the user can decide whether the transition is extremely gradual or a quick, sharp transition.