Contains core signal processing methods and classes, including: * Resampling (discrete up, down and up/down, polynomial up, and hybrid up/down). * FFT transform (forward and inverse). * DFT transform (forward and inverse). * Windows (Blackman, Hamming, etc.). * Windowed sinc filter for lowpass and highpass. * Dual windowed sinc filter for bandpass and bandstop. * Interpolation (linear and polynomial). * Data plotting via gnuplot (must be installed to use). * Delay line. * Biquad filters. * Envelope detector. * Conversion from dB-linear and linear-dB. * Oscillator with selectable wave type (sine, square, triangle, sawtooth). * Signal abstraction class.