Tail Delay - Delays the tail, but leaves direct and early reflections in place. Can be set to negative values to start the onset of the tail earlier.
The Rule - Think of Altiverb as an echo chamber. You feed your audio to the speaker(s) in the chamber, you put some mics in there, and get back the reverberated audio into the mixing board. The input of Altiverb goes to the speakers, the output of Altiverb is what the mics produce.

The Direct Sound - After the sound leaves the speakers, the quickest way to the mics is in a straight line. This first hit is the direct sound and its loudness and occurrence in time help you locate the speakers. The chamber itself is not heard in the direct sound, only the coloration of speakers, a bit of air, and the mics. You can choose to substitute this coloration by an uncolored, or flat version. To do this you turn the color knob from IR to flat.
Turn down
direct sound gain all the way if you use Altiverb as a traditional send (aux) effect, because then you just need actual reverb, which starts after the direct sound.

The Early Reflections (Early Refs) - come right after the direct sound. They are the first couple of reflections of walls, ceiling and floor of the chamber. Reducing early ref gain generally makes the audio more intelligible. It can also make the room sound larger or damped as soft reflections suggest far or baffled surfaces.

The Tail - is next. It's the long diffuse part that is normally called reverb.

-Switch off help by clicking