For those wondering what the typical response of THX ReEQ™ looks like, here is a frequency response plot with it engaged. While it's not the preferred two biquad solution, it just passes, since the total droop in energy in the 2K to 10K pass band closely mimics the original X curve correction. This response curve follows the digital, single biquad, low pass filter response. Sonic differences between these two types of filter responses are likely not audible in most applications given the much large variance of speaker responses and room interaction.

Editorial Note About THX ReEQ™ by John Dahl of THX

ReEQ was developed by THX's Tomlinson Holman in response to a request from the movie sound editors and mixers at Lucasfilm's Skywalker sound. The mixers found that when they listened to master tapes of their work on their home systems they sounded consistently too bright and edgy compared with what they heard in the movie dubbing stage where the masters were created. Movie dubbing stages are set up and calibrated to sound exactly like good movie theaters and vice versa. It's important to movie sound artists that they create the sound track while listening to the same system as the theater audience. In the movie biz this is known as accurate venue to venue translation.

In a movie theater the audience sits a long way away from the speakers, a theater is acoustically absorbent and the theater speakers have the high frequencies turned down slightly. In a home you sit close to the speakers, the room is acoustically live and the speakers do not have the high frequencies turned down. So you can see that a soundtrack recorded in a theater would sound bright when played back at home. The THX ReEQ filter compensates precisely for the response difference between a perfect movie theater and a perfect home theater.

The dubbing stage to theater translation is usually quite good but home theaters are another matter entirely. For example, a film played on a small TV without ReEQ may actually benefit by the high frequency boost while a decent home theater will almost always sound hard or edgy and therefore benefit from ReEQ.

Then there's the matter of the very small percentage of DVDs that have been "remixed for the home". That sounds like a good idea but who's system is it remixed for? How close will you sit to the speakers? How reverberant is your room? Etc, etc. Even when a disc is marked as remixed (which it may not be), these questions are impossible to answer in a technically and consistently useful way. This makes the THX ReEQ a known quantity based on idealized systems which can then be used or not as preferred by the individual listener.

Bottom line is… THX ReEQ, based on an ideal set of circumstances turns out to be quite useful even though home theater systems have wildly variable in-room responses making perfect corrections impossible 100% of the time.

Many thanks to John Dahl at THX for his background perspective on ReEQ.