An automatic gain control (AGC) for use in a digital radio receiver that allows at least two types of input signal to be processed using a single receiver front end by supporting two modes of operation, each optimized for one particular signal type, and a third mode not optimized for either. The AGC enables smooth switching between the optimized modes of operation via the non-optimized mode. By measuring a difference in the strength between the demodulated signals, and comparing that to two preset values, the AGC controls which mode of operation to place the receiver in. Modes of operation are maintained by adjusting the gain of a variable gain amplifier (VGA), so that an appropriate incoming signal is amplified to a level that is suitable for an analogue-to-digital (ADC) converter. The AGC is compatible with existing satellite digital audio radio system (SDARS) transmission capabilities.