In my last article,   we starting discussing the PowerQuad engine in the LPC55S69 as well as the concept of data in the “time domain”.    Using the Mini-Monkey board, we showed the function of collecting a bucket of data over time.     I chose to use a microphone as a data source as it is easy to visualize and understand.      You can now easily imagine replacing the microphone with *anything* that changes over time.     In this article we are going to look at some common algorithms for processing data in the time domain.  In particular, we will look at the “Dual Biquad IIR” engine in the LPC55S69 PowerQuad. An IIR biquad is a commonly used building block as it is possible to configure the filter for many common filtering use cases.   This article is not intended to review all of the DSP theory behind IIR filter implementations but I do want to highlight some key points and the PowerQuad implementation.