Bosso,

The digital PEQ itself is simply the device/tool used to apply filters to the signal. Automated room correction systems are more than a parametric equalizer. They have to measure what the room is adding to the overall sound and then decide which problems to address, how to deal with those with and then calculate the filters needed to ameliorate the problems.

Dismissing "how one arrives at what they intended to do to the input signal" and asking only about the notch filters is akin to asking what Rodin did with a chisel that other sculptors didn't. He hit it with a hammer, just like others did, and he chiped away at marble, just like other sculptors did. But that doesn't explain why he ended up sculpting something as enduring as The Thinker while his contemporaries didn't. The same tool will give different results depending on what you do with it.

To that end, MRC is different from most automated room correction systems (many of which also use a digital PEQ) in how it measures and what it chooses to correct. As mentioned in my post you quoted, most EQ systems measure amplitude and try to flatten out frequency response. By comparison, MRC measures in the time domain, looking specifically for frequencies that have long decay times, dialing them down to the average RT60 for the frequency range it is trying to correct.

So the difference between auto-EQ systems is not how they use their filters but what problems they use their filters for. For example: if your speaker had an amplitude peak at 55Hz, most auto-EQ systems (like the SMS-1) will use their filters try to bring it down so that it is flat. MRC won't touch it. Meridian explicitly states that flat frequency response is not the goal of MRC.

For a more detailed explanation (from the horse's mouth), check out Meridian's white paper on room correction here .

The paper references an AES presentation (The Loudspeaker-Room Interface - Controlling Excitation of Room Modes, Rhonda J. Wilson, Michael D. Capp, and J. Robert Stuart, Meridian Audio, AES 23rd Int'l Conference, Copenhagen, 2003) described here . This research was the basis for Meridian Room Correction.

If you find the description intriguing, you can purchase the paper from AES.