Truax has a pretty nice way of talking about acoustic structure at different scales. As a composer he's been an important proponent of granular synthesis, and as a teacher his way of talking about sound meshes rather neatly with the granular approach.
One issue he brought out in his keynote is how, over the past 100 years, our ways of listening have changed, and our sophistication as listeners. He's not just talking about professional or arty listeners, but all of us. In the past, our "acoustic environment" was pretty much synonymous with our immediate environment more generally. This (Truax argues) is one of the reasons that people in the 1910s seemed to be fooled by the sound of an opera singer on a phonograph record, a sound which to us comes across as a feeble imitation. But recording technologies have allowed us to abstract the acoustic environment from our immediate environment: we now have a felicity with embedded acoustic environments that is so sophisticated as to be casual. We know how to relate to the person sitting next to us on the tube listening to headphones; we understand the voices in the radio, why they have different reverb from the room we're sitting in, and why they can't hear us; we understand what is being hinted at when the narrator in a radio play doesn't seem to be in the same room as the characters.
Later that night, at the concert, there was a great example of embedded acoustic environments. We were listening to a multi-channel electronic concert, in a huge ex-ship-building shed ("No. 3 slip") in a dockyard. This hangar allowed plenty of sound in from outdoors, and so as the music played, it was... ahem... "augmented" by various other sounds: the dockyard's big clock chiming the hours; the firework-like sounds of artillery fire in a naval training ground; and also a heavily-echoed "Call Me" by Blondie!
I don't believe any of this was deliberate ;) but it's a great example of an embedded acoustic environment - and furthermore, the challenge that it presents to electronic composers. Composers need to be aware that the environment they're constructing will be usually played back over some speakers which don't form the entirety of the acoustic environment, but a sub-system of it, for the listeners. (Is this challenge equivalent to a demand to always be site-specific? Not quite, but related.) Some of the composers last night I think did not rise to this challenge, and it showed. But some of them did. Barry Truax was premiering a new piece called "Earth and Steel", written specifically for this place, and it worked great, it was very affecting.