What it does
Simple FIR "subtracting" comb filter built from scratch
Illustrates how to build a simple FIR subtracting comb filter from a delayed version of the signal connected, with a negative sign, in parallel with the original signal. This filter is known as a "Finite Impulse Response" (FIR) filter since the output depends only on the sequence of inputs (by contrast, an "Infinite Impulse Response" (IIR) filter utilises the previous outputs as well as the inputs). Play the DrawingBoard and observe the characteristic "comb" response displayed in the magnitude plot.
For a detailed discussion on this basic filter, see: "The Computer Music Tutorial", Curtis Roads, The MIT Press, 1996 (p.416).
Delays and gains are the elemental buliding blocks of all filters. Try building more elaborate filters from these basic blocks. Note that ASCII input and output files (included but unconnected in this DrawingBoard) are very useful when prototyping a filter design since they allow direct access to the exact input/output numerical data, without the scaling inherent to WAV I/O conversions.