Help needed to create a simple parametric Eq

I’m starting with the creation of VST plugins. All is going very well and I’m enjoying it a lot but I have come to a point where I would like to be able to add some EQ to the audio processors I’m creating.

I know there’s a filter DSP which can be used to create hi pass filters, and low pass filters, and band filters. My question is, how could I create a filter that allows me to increase the gain at a random frequency, and with a given Q, as you would do on a parametric EQ? I mean, what would be the right strategy? I’m not looking for code answers here, but more of an understanding of what would be the best way to add a bit of equalization to my own audio processors.


A straightforward implentation of such a filter is typically a biquad (e.g. second order) IIR filter. If you use the JUCE dsp::IIR filter, dsp::IIR::Coefficients::makeNotch computes the right filter coefficients for that type of filter

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@PluginPenguin Thanks for your answer. Does this mean that I could use a dsp instance of a IIR filter, and use the Coeffients class to calculate the coeficients (the parameters I guess) for the IIR filter so I can use it as a single “band” parametric equalizer, on a given frequency and Q?

Do you know if there’s any small code sample in the demos or anywhere to take a quick look to the implementation detail?

Basically, yes.

Have a look at this plug, authored by someone who posts here often. it will probably answer many of your questions.

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Thanks @AnoesisAudio!