An analog to digital converter (ADC) is a system that converts an analog signal, such as a guitar strum picked up by a microphone, and turns it into a digital signal. It does so by converting the analog voltage on a pin into a digital number. Simply put, it is a mixed-signal device that provides an output that digitally represents the input voltage or current level.
In audio recording setups, an ADC is an especially helpful audio accessory. That’s because most auditory data (voices, instruments, etc) is comprised of analog signals. In order to manipulate this data using a microprocessor though, you need an analog to digital converter to turn the analog signals into digital signals so that the microprocessor will be able to read, understand and manipulate that data.
There are several types of analog to digital converters, of course. The most common types are flash, successive approximation, and sigma-delta. These ADCs offer various speeds, use different interfaces, and provide differing degrees of accuracy. Be sure to choose the right analog to digital converter for your situation and desired finished effect.