An infinite impulse response (IIR) filter library for Linux, Mac OSX and Windows which implements Butterworth, RBJ, Chebychev filters and can easily import coefficients generated by Python (scipy). The filter processes the data sample by sample for realtime processing. It uses templates to allocate the required memory so that it can run without any malloc / new commands. Memory is allocated at compile time so that there is never the risk of memory leaks. All realtime filter code is in the header files which guarantees efficient integration into the main program and the compiler can optimise both filter code and main program at the same time.