ERLE (Echo Return Loss Enhancement) is the decibel measure of how much echo an echo canceller actually removes — the difference between the echo level entering the canceller and the echo level left in its output. A higher ERLE means more echo suppressed: figures of 20-40 dB or more indicate a strong canceller. It is the headline metric engineers use to evaluate and tune AEC implementations, often plotted over time to show how fast the filter converges after a delay change and how it holds up during double-talk. ERLE captures only the echo reduction, so it is read alongside speech-quality measures to ensure the canceller isn't winning on echo by damaging the near-end voice.
