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Category Archives: IIR Filters
About coefficient conventions
It’s been asked many times, so it’s worth an article explaining the conventions used on this site for transfer functions, and why they may differ from what you see elsewhere. People run into this most often with biquads: I use … Continue reading
Posted in Biquads, IIR Filters
7 Comments
Evaluating filter frequency response
A question that pops up for many DSPers working with IIR and FIR filters, I think, is how to look at a filter’s frequency and phase response. For many, maybe they’ve calculated filter coefficients with something like the biquad calculator … Continue reading
Posted in Biquads, FFT, Filters, FIR Filters, IIR Filters
27 Comments
Filters for synths—the 4pole
The last post noted that the two most popular synthesizer filters are the 2pole state variable, and the 4pole “Moog style”. And we started with the state variable—simple, popular, and delivering multiple filter outputs (lowpass, bandpass…) simultaneously. Here, we’ll follow … Continue reading
Posted in Digital Audio, Filters, IIR Filters, Synthesizers
5 Comments
Filters for synths–starting out
We haven’t developed a synth filter here yet… Filters we’ve presented Biquads. While they are useful for many simple cases of filtering, they are not a good choice for analog synthesizer emulation. Most notably, they are poorly suited to timevarying … Continue reading
Posted in Digital Audio, Filters, IIR Filters, Synthesizers
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Envelope generators—ADSR Part 1
After discussing the exponential decay of the onepole filter in a recent article, I couldn’t help but think about envelope generators. Besides, it would be handy to have one to test out some of these other components I’ve been writing … Continue reading
Posted in Envelope Generators, IIR Filters, Synthesizers
1 Comment
A onepole filter
Here’s a very simple workhorse of DSP applications—the onepole filter. By comparison, biquads implement two zeros and two poles. You can see that our onepole simply discards the zeros (the feedforward delay paths) and the second pole (feedback path): We … Continue reading
Posted in DC Blocker, Digital Audio, IIR Filters, Source Code
34 Comments