[Naagzh]

I hear mostly two types of "ambience", reverb and delays. The first sound is primarily a reverb with a long tail, or decay. As for the type of reverb, I'm not sure... maybe a large plate? There may also be a quarter-note delay mixed in underneath. Blending a reverb and a delay can make things more "lush" without crowding the lead vocal.

The effect on the 2nd vocal part is just a half-note delay, panned opposite the lead vocal. The delay signal has likely been filtered or EQ'd to sound more "low-fi" (the highs and lows have been rolled off, leaving mostly midrange frequencies).

These effects are created pretty easily within PT. Create a stereo aux track, insert a delay or reverb plug, set to 100% wet. Select an available stereo buss as the aux track's input (say buss 1-2). On the desired vocal track, create a "send" to buss 1-2 (the sends are on the little up-down arrows below the plug-in inserts). A send fader will pop up, which you'll need to raise to zero (they default to -infinity). How much you raise the send fader determines how strongly the vocal signal is sent to the reverb or delay.

To create another delay or reverb return, just create another stereo aux track and repeat.

Also, to thicken the sound of delays and reverbs, do a search on split harmonizer.