Wayne, It's not a question at being more adept or doing a better job than you are. It's more a difference in approach.

Frequencies with long decay times may not show up as problematic amplitude peaks. For example, a frequency that's bouncing back and forth between two walls will have a long decay time for every seat between those two walls. However, if you move a microphone between those two walls, you'll find places where that frequency might be softer than others or louder than others. Somewhere between those places will be a location where this frequency is around the same amplitude as other frequencies.

If your seat or your measuring location happens to be at that spot, the amplitude of that frequency will appear to measure flat. However, it will still be ringing and still have the long decay time. In a situation like that, amplitude based correction systems wouldn't detect a problem and wouldn't do any correction. A time-based correction system will see the long delay and calculate an inverse filter.

Likewise, there could be a situation where your speaker and room combine to create a loud hump around 60Hz at your listening seat. An amplitude based correction system will try to correct that, to bring the volume level in line with other frequencies. A time-based correction system will check for unusually long decay time and, if it finds none, will do nothing. You'll still have the amplitude hump.

So it is two different approaches, each of which can sometimes totally miss a problem that the other is addressing. Agreed. Removing energy from a frequency that is bouncing back and forth between two walls in an attempt to lower its decay time can also make it appear quieter (and bring it more in line with other frequencies). But if the the latter were the goal of the Lex/Meridian systems, they wouldn't be going through the added effort of measuring in the time domain. So much easier to simply look for the loudest and most offending peaks and try to bring those down. That's what most of the EQ systems on receivers do. Precision aside, there is nothing magical about the parametric EQ used by Meridian, Lexicon, Audyssey and H/K. They're basically used to remove energy from a particular frequency.

The trick is being able to recognize which peaks correlate to long decay times and which ones don't. The Lex/Meridian systems can not only tell the difference, but they only attempt to correct the ones that correspond to long decay times, leaving the others alone.

Wayne, if you see four peaks between 20Hz and 250Hz, what method do you use to tell which of those has unusually long decay times and which ones don't? What if it is measuring from a location where a certain frequency isn't peaking in amplitude but does have a long decay time? If you believe it is correcting for peaks, then it will apply no correction there. If you believe it is correcting for decay time, then it will apply correction there. Which is it?

BTW, since it can't fix all the problems, it only goes after the most severe ones. For each of the 10 channels it corrects (7 main channels and 3 subs), up to 7 filters can be used. In practice however, Dr. Muller has said that they've never run into a situation that required more than 3 or 4 filters per channel.