Also known as: automatic gain control, AGC

Automatic gain control (AGC) adjusts amplification to keep a signal at a usable level — high enough above the noise floor but below the ADC’s clipping ceiling (0 dBFS).¹

AGC continuously adjusts gain so the output level stays roughly constant despite a fading input.

How it works

AGC can live in the tuner hardware or in software. For decoding a fixed system it can “pump” — ramping up in quiet moments and clamping on strong bursts — which is why a well-chosen manual gain is often preferred.

Relevance to SDR

Setting gain correctly is the single setting beginners most often get wrong; see the gain lesson for a practical routine.

Sources

1. Automatic gain control — Wikipedia, on closed-loop gain adjustment and headroom. ↩

See also

• dBFS
• Analog-to-digital converter (ADC)
• Noise floor
• PPM frequency correction

Learn it step by step

• Gain, AGC & avoiding overload

From the blog

• SDR Internals, Part 4: DSP foundations — filters, NCO & AGC