when using the FFT for DSP should I convert the A to D samples back into a Voltages ? so A to D sample = sample voltage * ( bits / max Voltages) so sample Voltage = (A to D sample ) *(max Voltages/ bits) that is right, right? anyhow should I keep the samples as digital samples or convert them to analog samples before I run them in to the FFT? why or why not? I kind of think it should matter... but I do not know . I am new to this. I do think that the A to D / mic on a computer might remove all the negative numbers, but i do not know is you would get negative numbers from a microphone... do you ?