This Ableton walkthrough covers two character controls inside Echo: the overdrive dial and the Feedback knob. Pushing the overdrive dial past 0 dB adds distortion to the delay signal, and clicking the D button dials in a heavier distortion mode for a more saturated, degraded texture.
The Feedback dial controls how much of the delayed signal gets fed back into the delay lines. Keeping it below 100% gives you standard repeating echoes, but pushing it above 100% creates increasingly extreme, self-reinforcing feedback. A practical note: be careful with feedback above 100% at high monitoring volumes, especially on headphones.