[Wayne A. Pflughaupt]

macrae11 wrote:

I'm not familiar with how these softwares could correct in the time domain to correct a room node that cause a(for example) low D to sound twice as long as it sounds in the program material.

I will research it a bit more, but if you have a simple explanation that could enlighten me, I would welcome it.

From the little I’ve seen, they don’t really have much effect on time domain. I haven’t seen any comprehensive in-room testing, other than Ethan Winer’s EQ vs. Bass Traps extravaganza. The test has some problems, though, mainly that the sheer number of measurements to sift through is mind numbing, and the guy who set up the equalizer did a really, really bad job of it.

Ethan also did an evaluation of the effectiveness of the Audyssey MultEQ DS-21 mentioned, which claims to reduce extended signal decay (aka ringing). His conclusion was that it was a mixed bag as far as dealing with ringing was concerned.

Since there seems to be a dearth of any comprehensive in-room testing, other than these two (which are the only ones I’m aware of) I’ve done some of my own, although I haven’t explored it fully or posted any results here at the Shack. After studying waterfalls ‘til I’m bleary-eyed, I’ve found pretty much the same thing as Ethan, that it’s a mixed bag using an equalizer as a fix for extended low frequency room decay.

From what I’ve seen, the improvement waterfalls show for modal (or “time-domain”) EQ filtering has only been apparent in the short-duration 300 ms window. When the window is lengthened to 600 ms, any advantage modal filters showed over other equalizing techniques pretty much vanished.

Here is a sample to show what I’m talking about. The Hz markers represent peaks that REW found, and the “Modal Filters” waterfalls have REW-recommended filters set at those frequencies (except for the red 49 Hz marker). The “Smoothing Filters” graphs show the result of filtering that ignored REW’s recommendations and used four filters that merely smoothed response. Notice that this “faster decay, but only up to a point” effect is especially noticeable for the 26.9 and 23.5 Hz markers. As you can see, once the window is lengthened to 600 ms, any apparent advantage of modal filtering over smoothing virtually disappears. (Hit F11 and you should be able to get all four graphs on your screen at the same time.)

Modal Filters at 300 PP 14-01-34.JPGSmoothing Filters at 300 PP 14-08-30.JPG
Modal Filters (Left) vs. Smoothing Filters (Right) @ 300 ms


Modal FIlters at 600 14-01-34.JPGSmoothing Filters at 600 PP 14-08-30.JPG
Modal Filters (Left) vs. Smoothing Filters (Right) @ 600 ms

You can see the same effect in Ethan’s “with and without Audssey” comparison graph. Notice the broad peak between 20-56 Hz, where Audyssey seems to improve the rate of decay in the short term, but ultimately does not reduce or eliminate it in the long term. Also note that even significantly reduced gain of the same peaked area effected by the equalizer did not reduce the ringing.

Regards,
Wayne