While most folks are are familiar with the “Graphic Equalizer” – arguably the most abused special effect after reverb and echo – I’ve not witnessed to many live engineers and in particular theatre sound engineers using Parametric EQs often. A great pity as they are an awesome tool, once you get used to them, and useful in a variety of situations.
Typically a graphic equalizer shapes a sound in a predictable way, used property it is a good tool to use when “tuning a room”. But the Parametric is a different beast. It allows you to shape your sounds in ways that you want – and in some instances – in ways you’d not imagined if you’ve never used one before.
To appreciate this it’s important to understand what an equaliser (EQ) is. Simply put it’s a filter that you use to enhance or dampen, cut and boost certain frequencies. EQs can have both fixed – Graphic EQs – and dynamic frequencies – Parametric EQs.
While Parametric EQs come in a variety of shapes and sizes these days a fundamental, basic Parametric will have at least 3 main controls to shape frequencies.
- Bandwidth selection
- Frequency selector
- Gain.
Essentially gain allows you to preset how much the filter will boost or cut the desired frequency. The trick with Parametrics, if you’ve never used one before, is to get used how they operate by sweeping though the frequencies. By sweeping though (adjusting gain etc) you’ll be amazed at just how much of a difference can be achieved with this seemingly simple but incredibly powerful tool. If I was given a choice between a 64 band Graphic EQ or a 10 band Graphic EQ and a Parametric it’d be a no brainer – the last two would serve a far wider range of situations.
Example usage includes setting the gain to a high level then sweep the frequency through its spectrum. Using it this way can help to diagnose poor and problem frequencies and is an excellent technique for diagnosing problems with your tracks because some frequencies will sound hard or unpleasant when you listen – while others can be tuned to sound golden.
An old studio engineers trick is to lower the frequency on your high end sounds to around 60-200 Hertz. This can help to produce a lot more room in your mix. In addition it can make the low frequencies in your mix stand out. Excellent for throaty instruments like drums and bass.
There’s Parametric EQs on the market now that can enhance frequencies that are “missing” and allow them to be added back in. Essentially they add harmonic frequencies to the original sound that acts kind of “Ultra-Tune” only for frequencies. 
Not a bad trick for those cruddy, lifeless MP3 sound effects you want to use but cringe over.
Scott Kane