Minimal EQ, Target Levels, and a Hard-Knee House Curve
It’s time to re-think the way we equalize
It’s time to re-think the way we equalize
Better late to the game than never
It’s been a little over a year since Sonnie dragged me into the 21st century, convincing me to start using REW and the Behringer DSP-1124 digital parametric equalizer (thanks again, Sonnie!). It’s been a peculiar combination of elation and frustration.
Certainly, it was a delight to ditch the time consuming manual method of plotting frequency response for REW’s ultra-slick, instant results.
The frustration? Well, things never sounded as good as they looked on the screen. Don't get me wrong, "with EQ" always sounded better than "no EQ." But I was never completely happy.
For instance, my favorite test track for checking bass, Basia’s “Ordinary People” from her London Warsaw New York CD. This track features a bass line that runs up and down two full octaves, so it’s great for determining (a) if a subwoofer has linear response, and (b) if it’s blending well with the mains.
Well, it just wasn’t right. The lowest notes didn’t come through the way I’m used to hearing (and feeling) them, and the upper notes sounded bloated and overemphasized. The subs were clearly “invading” the mains’ lower reaches, but turning them down for a better blend meant the lowest notes were even worse.
Every few months I’d get frustrated and run REW again and re-equalize – and end up with pretty much the same thing, albeit with a different set of filters.
I think REW’s terminal coolness probably had an adverse effect, discouraging me from taking the trouble to get to the root of the problem. After all, I probably told myself subconsciously, response that looks this good has to sound good! You’ve never had these powerful tools at your disposal, so you’re just not used to hearing "correct!"
I may have discontentedly left it at that, except that I recently noticed something rather distressing with the Basia track that had previously escaped my notice: Certain bass notes were coming through noticeably lower in volume than the notes before and after. And elsewhere, a note or two slightly hotter than those adjacent. What was up with that? I’d never had that problem before, when I was using much-less-precise 1/3-octave equalization.
Here is the baseline response I’ve been working with since we moved into this house a couple of years ago:
I’ve never been able to get anything resembling an appropriate-looking graph with less than 7-8 filters. Here are a couple of equalized graphs, the second being more recent.
Equalized Response with 7 Filters
Equalized Response with 8 Filters and 6 dB House Curve
Filter Panel for Above
Getting to the root of the problem
Certainly, they aren’t bad looking graphs. As the baseline graph shows, my measured response peaked substantially above the 75 dB Target Level. Naturally, I followed the more-or-less standard protocol and equalized towards the Target.
Helping numerous people with their equalizing issues on this Forum, I’ve noticed this is a familiar refrain. The problem is that equalizing towards the Target Level requires more filters than would be necessary if you say, just raised or lowered it to a good mid-way point between the worst peaks and depressions. In some extreme cases we’ve seen people attempting to equalize a fairly easy curve with 9, 10 or even 11 filters, in order to hit the Target Level. In my case, you can see by comparing the baseline graph to the 8-filter panel that the majority of filters used - five of the eight - were “spent” realigning the ~22-42 Hz area down to the Target Level.
“The problem” – is over-equalizing really a problem? Well, at the pro audio forums, where people use equalizers for a living, the prevailing wisdom is “use as little as necessary to get the job done.” Of course, equalizing a subwoofer in a small room is a lot different from what those guys are doing, tuning a full-range system in some big auditorium. So does the “keep it minimal” advice apply to us?
As we shall see - probably so.
For my latest re-equalizing attempt, I tried a new tact – raising the Target Level up between the peaks and valleys before equalizing. Here is the result.
Equalized Response with 81 dB Target and 6 dB Hard-Knee House Curve
Yes, you’re seeing correctly: four filters. In my case, I got lucky in that my sagging response above ~45 Hz played right into the hands of the hard-knee house curve I wanted, which enabled me to use fewer filters. Furthermore, I decided to avoid equalizing close to the crossover point (above ~70 Hz or so in my case, with a 90 Hz crossover), since any equalizing up there will probably be blown out by the main speakers once they’re added. (Of course, that needs to be double-checked before locking down your filters, but it was true in my case.)
So - how does it sound? Absolutely fabulous. I’d have to say my bass response has never sounded this good! Most of the improvement I attribute to the hard-knee house curve, which we’ll discuss later. (For the impatient people who want the “how does it sound” details now, scroll down to the Hard-Knee House Curve post, “The Holy Grail of bass?” heading.)
And - remember the problem with the “hot and cold” bass notes in the Basia track? Well, that is totally and completely gone. Each and every note is now at an appropriate and consistent volume from one to the next!
Folks, there’s simply no that way realigning a house curve could have solved that problem. The uneven bass notes could only have been a by-product of poor equalization. Or more precisely, equalization that had no business being there to begin with.
Compelled to excess?
So - where have we gone wrong? In at least a few ways, in my opinion. We’ve already opened the door to the Target Level situation: If you don’t properly realign it after taking your baseline measurement, it may require a lot of unnecessary filters to instead realign your response curve. This is true if you equalize manually, like I do, or if you let REW auto-equalize. Wholesale level adjustment via a multitude of filters is poor use of an equalizer. The REW help files clearly indicate that the Target may need to be shifted before applying filters; I don’t know how we managed to get hung up on the 75 dB Target as a quasi-rigid standard.
To a lesser extent, I think our standard recommendation of not smoothing graphs is another problem stimulating the urge to over-equalize, since an unsmoothed graph exaggerates the peaks and valleys the graph displays.
Another big problem, I feel, is the window in REW that we use here. Early on we decided that all graphs presented for evaluation should have an amplitude spanning 45-105 dB (i.e. the vertical scale), in the interest of comparing “apples to apples,” as it were, from one Member’s graph to the next. Of course, that was and still is a laudable goal. From time to time people have presented graphs with a larger-amplitude window – say, 20-130 dB, which results in a response line that’s “squeezed” tighter – i.e., less exaggeration between the peaks and valleys. That Member would inevitably get an advisement from our resident experts that the window setting they were using was being generous to their response, making it appear better than it really is.
I submit that the opposite is a more accurate reality, that the narrow 45-105 dB window makes response look worse than it sounds. It generates a scary-looking graph that compels people to over-equalize in an effort to make things “look” correct.
Yes, a wider 20-130 dB window will visually flatten out the curve. But in my opinion, it’s a more accurate representation of what the response you’re seeing on-screen truly sounds like. And since the curve “looks” better going in, there’s less of a compulsion to equalize it to death.
For instance, my equalized response in the Hard Knee graph above, shown in a 45-105 dB window, still looks fairly ragged, but in “real life” it sounds as smooth as melted butter. In other words, the 45-105 dB window is a poor reflection of what I’m hearing.
This was actually one of my earliest reactions after EQing with REW: Visually, there was a huge improvement in the way my equalized response looked. But switching the equalizer in and out, it was obviously that the audible improvement was much more subtle than it appeared on-screen in the 45-105 dB window.