There's a function I think could be useful for system response measurement: f(x)=sin(pi*(fH-fL)*t)*cos(pi*(fH+fL)*t)/t
it's basically the ideal bandpass function, it's fourier transform is 0.5 between fL and fH and 0 everywhere else. There's another related signal, the sinc... but what should this one be called? "cosinc" is already taken--it's the name of the derivative of the sinc. sincos? sounds silly Chuck