Parametric EQ

I’ll give it a go 🙂

There are three terms to be familiar with when using a parmetric EQ – gain, frequency (or center frequency), and bandwidth (or "Q").

"Gain" refers to how much you are boosting or cutting the amplitude (level) of the audio in a particular band. Gain is expressed in dB (decibels).

"Frequency" – sometimes expressed as "Center Frequency" – is the mid-point of the given band. An equal range of frequencies above and below this center frequency will be affected by the boost or cut in gain, as determined by the next factor – bandwidth.

"Bandwidth" or "Q" refers to how narrow or wide a range of frequencies you’re adjusting, sometimes expressed, as you pointed out already, in octaves. Bandwidth is understood to refer to a range in which the levels have risen or fallen by a maximum of 3 dB.

You can think of an octave in two ways. If you’re familiar with a piano keyboard, an octave is a range of 12 notes a half-step apart in pitch from one another. The range from middle C (C4) and the next C up on the keyboard (C5) is one octave.

As it applies to a parametric EQ, however, it’s better to think of an octave as the interval between one musical pitch and another with half (lower pitch) or double (higher pitch) its frequency. To make the math easy, let’s say you have a note that plays at 440 Hz (which happens to be the A above middle C on the piano). The A above it has a frequency of 880 Hz. The A below it has a frequency of 220 Hz.

Bandwidth can be adjusted from a tiny sliver of an octave to target a very narrow and specific frequency range, to a very broad range of up to 3 octaves or so. The lower the bandwidth, the fewer frequencies will be adjusted. The higher the bandwidth, the more frequencies will be adjusted.

With me so far? 🙂

Here’s where it gets tricky. Although "Bandwidth" and "Q" are often used interchangeably, and both refer to a particular range of frequencies, they are expressed in inverse scales. That is, a higher "Q" number means a narrower range, whereas a lower "Q" represents a wider range. For example, a "Q" of approximately 29 (trying to keep the numbers round here) translates to a mere 1/20th of an octave, while a "Q" of 0.40 affects 3 whole octaves.

With all of that in mind, let me offer a couple of real-world examples.

Let’s say you want to increase the amount of bass with a parametric EQ. If you set the center frequency low, say, 50 Hz, and set the Q high (for a narrow bandwidth) you can increase the amount of "low" bass you hear – kick drum, lower bass guitar, etc., without causing any mid-bass boost which might result in a muddier sound on a higher end system.

Or, let’s say you have smaller, bass-shy speakers that can’t reproduce lower bass notes. You might choose a higher center frequency – say 120 Hz – and a lower Q (for a wider bandwidth) and "warm up" the sound, compensating somewhat for the deficiencies in the speakers.

If you want to hear the effect of the settings best, I suggest picking a middle frequency – say, 1 kHz – and boost it a good amount – say, 10dB – with the Q set to mid-scale on your EQ. You’ll now become familiar with which parts of the audio "live" in that range. Leave everything else the same and cut the amount by 10dB and take note of what disappears. Widen the range and notice how a broader portion of the spectrum is affected. Move the center frequency up or down and see what effect that has. Experiment!

The bass shape control in Breakaway actually changes two of these factors simultaneously – center frequency and bandwidth. When used with the bass boost/cut slider, you can get pretty precise control over the quantity and texture of the bass. (These controls also affect compressor thresholds and maybe band outputl levels (?) in the multi-band processor section as well, but that’s another topic altogether…)

Leif or Jesse, please chime in if I haven’t described that function of Breakaway fairly or accurately!

Hope that helps some and didn’t muddy the waters further for you 🙂

Jim