Category Archives: IIR Filters

Biquad C++ source code

I don’t want to get into the business of teaching people how to code—there are a huge number of free resources available on the internet to that do that. But I’ll give a small taste for those trying to get … Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters, Source Code | 65 Comments

Biquad formulas

For fixed filters, we can plug biquad coefficients into our programs. But often, we need to calculate them on the fly, to user settings or changes in sample rate. As a companion to the biquad calculator, here are the formulas … Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters | 40 Comments

A biquad calculator

Something useful: a biquad filter coefficient calculator… Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters, Widgets | 37 Comments

The bilinear z transform

The bilinear transform is the most popular method of converting analog filter prototypes in the s domain to the z domain so we can implement them as digital filters. The reason we are interested in these s domain filters is … Continue reading

Posted in Digital Audio, Filters, IIR Filters | 23 Comments

The digital state variable filter

The digital state variable filter was described in Hal Chamberlin’s Musical Applications of Microprocessors. Derived by straight-forward replacement of components from the analog state variable fiter with digital counterparts, the digital state variable is a popular synthesizer filter, as was its … Continue reading

Posted in Digital Audio, Filters, IIR Filters | 17 Comments

Biquads

One of the most-used filter forms is the biquad. A biquad is a second order (two poles and two zeros) IIR filter. It is high enough order to be useful on its own, and—because of coefficient sensitivities in higher order … Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters | 26 Comments

Pole-Zero placement

Use the new, improved pole-zero calculator—but be sure to read the “Experiments with standard biquads” section below for tips on placing poles and zeros for standard filters. Here’s a Java applet that illustrates pole-zero placement. It lets you design a … Continue reading

Posted in Biquads, Digital Audio, Filters, IIR Filters, Widgets | 8 Comments