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One of the confusing things for many people new to DSP equalization (EQ) is the choice between graphic and parametric EQ. In this application note, we explain the difference.

Parametric EQ

In a parametric equalizer, each filter cuts or boosts a range of frequencies. Each filter has three controls:

  • frequency: the center of the frequency range to be cut or boosted

  • gain: the amount of boost or cut

  • Q: the "sharpness" of the boost or cut, with higher Q meaning a narrower filter

Parametric EQ thus allows a single filter to be very narrow or quite wide, and it is therefore very useful for correcting frequency response errors in a loudspeaker or reducing peaks caused by room modes. When implemented digitally, parametric filters can also take the shape of a "shelving" filter, which boost or cuts frequencies above or below the filter frequency.

The screenshots below show four filters in use: a low-shelf filter (boost), a narrow notch, a broad boost, and a high-shelf filter (cut). First the frequency curve as shown in an older version of the miniDSP software:

Setting parametric EQ in the miniDSP plugin

Here is the frequency response measured with Room EQ Wizard:

Measured response of the parametric EQ

Most of the current miniDSP processors support parametric EQ on each output channel, with ten filters in each. The processors that do not have Dirac Live typically also have a parametric EQ block with ten filters on each input channel. Check the User Manual for each product of interest to be sure.

Graphic EQ

A graphic equalizer has a number of filters spread evenly across the audio bandwidth. Each filter is the same shape, and has just one control: the amount of boost or cut. The filters overlap, so the combined response forms the shape given by the positions of the sliders. Most common is the third-octave 31-band graphic EQ, with center frequencies from 20 Hz to 20 kHz.

Graphic EQ can be implemented with analog circuits or with digital signal processing. While miniDSP products no longer support graphic EQ, here is an example from an older version of the software, set to approximately the same response as the PEQ above:

Setting graphic EQ in the miniDSP plugin

Here is the frequency response measured with Room EQ Wizard:

Measured response of the graphic EQ

Which to use?

Provided that you have a measurement microphone and software set up, the parametric EQ is ideal for correcting speaker and room response. Because of this and their great power and flexibility, current miniDSP products only support parametric EQ.