Do you recognize this filter?
This is a digital state variable filter. Note that your pseudo-code of the filtering process is not correct. You replaced all += in the original code by =, which results in a filter that wouldn't work as desired.

The actual recursive equations implemented by the code are

$$\begin{align}l[n]&amp;=l[n-1]+fb[n-1]\\
h[n]&amp;=q\big(x[n]-b[n-1]\big)-l[n]\\
b[n]&amp;=fh[n]+b[n-1]\end{align}\tag{1}$$

where $l[n]$, $h[n]$, and $b[n]$ are the low-pass, high-pass, and band-pass outputs, respectively. The equations $(1)$ implement a second-order IIR filter (actually three).