Digital Signal Processing (DSP) is a branch of signal processing dealing with the analysis and manipulation of digital signals.  Most digital signals have their origin on analogue signals.  Analogue signals are converted to a sequence of numbers, taken at regular intervals from the signal through what is termed an analogue to digital converter (ADC).  Once in digital form, these signals can be analyzed and operated with DSP methods and converted back to analogue form via a digital to analogue converter (DAC).