The device consists of two pairs of analog input pins (INxP and INxM) as differential inputs for the recording channel. The device supports simultaneous recording of up to two channels using the high-performance stereo ADC. The input source for the analog pins can be from electret condenser analog microphones, micro electrical-mechanical system (MEMS) analog microphones, or line-in (auxiliary) inputs from the system board.

The voice or audio signal inputs must be capacitively coupled (AC-coupled) to the device and, for best distortion performance, use the low-voltage coefficient capacitors for AC coupling. The typical input impedance for the PCM1820 is 2.5 kΩ for the INxP or INxM pins and 10 kΩ for the PCM1821. The value of the coupling capacitor in AC-coupled mode must be chosen so that the high-pass filter formed by the coupling capacitor and the input impedance do not affect the signal content. Before proper recording can begin, this coupling capacitor must be charged up to the common-mode voltage at power-up. To enable quick charging, the device has a quick charge scheme to speed up the charging of the coupling capacitor at power-up. The default value of the quick-charge timing is set for a coupling capacitor up to 1 µF.