Microcontrollers are purely digital devices which work on logic0 and logic1 voltages; still they are widely used for analog signal processing. There are specialized signal processors chips available which are custom made for particular applications; however a general purpose microcontroller is more than enough for small kind of signal processing applications like audio signal input and output. The microcontroller can read the analog input voltage by sampling it and converting it to their digital values. The Analog to Digital Converter (ADC) available in almost all the microcontrollers help in this task.  A timer can be used to generate the sampling time period. The sampled values can then read and modify by the microcontroller. The modified signal is then output by the microcontroller in the form of Pulse Width Modulated (PWM) waves. Most of the microcontrollers have the PWM module which helps them in generating analog voltage output at an external device.