Shelving Equalizer

Frequency Range

Equalizers are usually described using a "flat response curve." This means that a system or piece of equipment responds equally to all frequencies within a specific range. This range is usually set to 20 Hz to 20 kHz. If some frequencies are boosted or cut, describing the frequency response graph using a visual analogy is useful.  

Shelving Equalizer 101

In a shelving EQ, a band of frequencies is boosted or cut either in the high-frequency end of the spectrum or in the low-frequency end. 'Shelving' is not a term that is ever applied to a mid-range boost or cut. So, in a shelving EQ, all frequencies are boosted or cut by the same amount. The exact change in level is applied to the limit of the frequency spectrum. Other forms of EQ include the 'bell' where a particular band is boosted, but higher and lower than that, the response returns to normal. Another type steadily increases the response towards the end of the spectrum. However, this is not common in sound engineering practice.

Flat Cut

The shelving equalizer offers the peak/deep response on the side of the selected center frequency and a flat cut or boosted region. A broad equalization desire might be to add brightness to the sound. A high-frequency shelving equalizer increased for 6 dB at 8 kHz will raise the output from about 8 kHz and above. It is not limited to a center frequency or its associated bandwidth. The resulting alternation in frequency response is flat (like a shelf) beyond the selected frequency. The concept of shelving equalizer applies to low frequencies, high, and cuts and boosts. In all cases, a flat region is beyond that selected center frequency, which is boosted or attenuated.  

Listen Intensely

The transition back to the unprocessed region is half of the bell curve of a peak/dip contour. Therefore, the 3 dB down point the bandwidth and the Q also apply to the shelving El. Boosting by 9 dB at 10 kHz and above is, in fact, a 3 dB down (+6dB) at 10 kHz, achieving the full boost (9 dB) a little bit above 10 kHz. Below 10 kHz, this shelving EQ is thought not to be processing the signal. This is true well below 10 kHz, but just below 10 kHz, the shelving EQ starts to lift the signal amplitude. A high-Q shelf abruptly transitions from the region of unaltered frequency response to the region of the 9 dB boost. A low Q spreads that transition out across a broader spectral region. Both approaches have production value in the right circumstances, so the engineer must pay attention and listen intensely.  

Easy to Use

Since shelving equalizers have few controls and work on the audio spectrum's two most easily identifiable components (bass and treble), they tend to be among the easiest equalizers to use. However, what the shelving equalizer gains in ease-of-use it lacks in flexibility. This effectively limits you to just tailoring the essential timbral qualities of a sound, whether adding a little bit of high-end sparkle or some extra bass-end weight.