DSP is usually used with real-world analog signals found in our lives , the first step is usually to convert the signal from an analog to a digital form , by using an analog to digital converter . The goal of DSP is usually to measure , filter and\/or compress continuous real-world analog signals . The first step is usually to convert the signal from an analog to a digital form , by sampling it using an analog-to-digital converter ( ADC ) , which turns the analog signal into a stream of numbers .