Originally Posted by walbert
I've never seen a receiver with ASA, so I'm not certain of this.
OK, it's apparent you can't explain it in your own words because you don't actually know what ASA is. In that case, let's start at the begining.
Ever hear of Hughes SRS or Spatializer? It was the kind of crosstalk cancellation processing that made a pair of speakers sound like they were further apart than they physically were. It was popular for TV sets, giving almost a pseudo-surround effect from the two built-in speakers.
That's basically what ASA is. And that's why, during initial set-up of a THX receiver, you had to dial in how far apart your rear speakers were. The wider apart they were, the less SRS processing they needed. THX wanted you to place the speakers close together only to then apply spatializer-like processing to make them sound like they're further apart. Seriously? Better and simpler solution: spread the speakers apart physically (instead of virtually), like they used before the Ultra2 spec.
ASA is completely different technology than Lexicon's LOGIC7 and Yamaha's CinemaDSP that you were likening it to; not even in the same category. Think of surround processing as coming in two flavours: extracted ambience and generated ambience.
CinemaDSP is an example of the latter, as are the various Hall, Club, Church and Stadium modes you see on some receivers. They generate reverb and early reflections in order to give the impression of a larger listening space. Nothing wrong with that, as long as you understand that they add things (echos, reverb) that weren't in the original recording.
Yamaha even goes the extra step of sampling the impulse response and decay characteristics of real-life venues for some of its DSP modes (hence specific mode names like Roxy Theatre, Village Vanguard, Bottom Line, etc). Sony does the same with some of their theatre modes, which sound remarkably like their screening rooms here in Los Angeles. If room simulation is your preference, then these are the modes for you.
By comparison, LOGIC7, Dolby PLII (IIx, IIz), DTS Neo:6, Neural, Circle Surround, etc, are examples of ambience extraction. They use only the sounds in the recording itself, steering them to various speakers based on intensity and phase. Nothing is added. With 2-channel material, correlated (in-phase) mono sounds go to the centre speaker, which is where those sounds would have phantom imaged anyway. Decorrelated (out-of-phase) info is steered to the surround speakers. With 5.1 material, surround information that would normally have phantom imaged behind you is extracted and steered to the speakers behind you. The remaining surround information is sent to the speakers at your sides.
So, ASA (which is only applied to the rear speakers) is nothing like LOGIC7 which is nothing like CinemaDSP. And it certainly isn't some magic bullet that can compensate for poor speaker placement. Spreading the rear speakers apart makes it easier to hear stereo separation back there, allows for smoother pans around the surround field, improves rear envelopment, minimizes imaging reversals, prevents hot-spotting in the middle of the back wall, etc. Those are amongst the reasons why I think placing the rear speakers together is a bad idea. Like I originally said, it is one THX recommendation that doesn't make sense.