This page is a landing page to direct the reader to pages on the principles of various delay effects.
As a non-user, and definitely a non-expert, in these effects I can't see what the basic difference is between Delay and Echo, particularly with regard to their implementation in Audacity. Echo effect seems to be just a "poor relation" of the Delay effect just with fewer controls (though it does carry a simple delay parameter). Am I right or wrong?
Accordingly I am "commenting out" this potential page-link for now.
"Thought of" as modulation effects
The following are often "thought of" as modulation effects (because they sound like thay are modulating), but they are really delay effects:
The following are true modulation effects