The latency of any RTAS plug-in in a ProTools 7 is dependent on your ProTools hardware buffersize.
Adjust hardware buffersize in ProTools 7 via menu Setups->Playback engine
If it is set at 512 samples the total latency is

512(PT7 hardware buffer) + 512(PT7 hardware buffer) + 256 (Altiverb) = 1280 samples

This is 26 milliseconds at 48 kHz, well under usual pre-delays for reverbs.

The upcoming TDM version of Altiverb works around latency alltogether, but as long as Altiverb is RTAS in ProTools 7 we cannot avoid Latency.

Q: I have an Altiverb HTDM License, and I get to see all these options in my plug-in popup. What do they mean ?

1. Synonyms for backward compatibility

In ProTools 6.9, there were two Altiverb plug-ins, the HTDM and the RTAS version of Altiverb Internally ProTools knew them by different names than the names you see in the popup.

Then Digidesign drops the HTDM format in ProTools 7 alltogether.
ProTools 7 will not be able to find, or insert the HTDM plug-in any longer.
So every ProTools 6.X project where originally there was an HTDM-Altiverb inserted, ProTools 7 will start looking for it, can't find it and will drop the plug-in from your the project. So old ProTools 6.X projects won't come up with the Altiverbs inserted. Big problem, lots of angry people.

So we decided to kind of double install the Altiverb 5.4.4 RTAS plug-in, or at least make a single plug-in known to ProTools 7 by both original names. Consequence is that often you see one plug-in with two names in the plug-in insertion pop-up. Let's call them synonyms.


2. Surround in a mono track ?

ProTools offers the possibility to insert surround plug-ins on tracks with only two outputs. The rest of the outputs of such a surround plug-in are available in the input popup of any other mixer strip. Just like you'd pick up a bus-channel there, you can pick up Altiverbs rear reverb channels.

Altiverb explains to ProTools the amount of input/output channels that it will accept/leave on the mixer strip it is inserted on.
This is displayed by ProTools between round brackets ( ).

Whatever is between < > is the actual amount of output channels Altiverb generates. When Altiverb outputs more channels than it leaves on the mixer strip, they are available on other mixer strips.

Knowing these two things, the synonyms and the surround options, we can explain every Altiverb you see in, for instance, a mono mixer strip insert:

f
Altiverb 5 (mono)
Altiverb 5 <mono> (mono)
The above two are synonyms. They function the same. They accept one input channel and output just one channel of reverb.

Altiverb (mono/stereo)
Altiverb <stereo> (mono/stereo)
The above two are synonyms. They function the same. Both take one input and output two channels of reverb.

Altiverb <5.0> (mono/stereo)
This Altiverb inputs one channel, leaves two channels of reverb on this mixer strip. Three more reverb channels (center Ls end Rs) for surround use are available as inputs in the input popups of other mixer strips.

Altiverb <5.1> (mono/stereo)
This Altiverb inputs one channel, leaves two channels of reverb on this mixer strip. Four more reverb channels (center Lfe Ls end Rs) for surround and sub use are available as inputs in the input popups of other mixer strips.

Altiverb <quad> (mono/stereo)
This Altiverb inputs one channel, leaves two channels of reverb on this mixer strip. 2 more reverb channels (Ls end Rs) for quadrophonic surround are available as inputs in the input popups of other mixer strips.