Preset vs Reset

Preset vs Reset

Preparing some of the new QSC K.2 series boxes for a club install and have some data here from the verification step of the process. I thought it was interesting enough to share, and there’s a couple of things I found thought-provoking, as it’s my first time working with this particular product.

These boxes come with onboard DSP that allows HPF, EQ, delay, and eleven preset tunings. Here’s a nifty animation showing how each of the presets compares to the raw response. (1/12 oct smoothing)

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To address the obvious question, no, it’s not a flat line. I measured the loudspeaker in the real world, where it’s going to be used, not in a lab. Rather than the line itself, what I’m pointing out here is the differences in each of the presets.

I personally find the gain reduction on some of these presets rather alarming. I would have assumed that the tunings simply changed the EQ curves, but a handful of these have pretty severe attenuation as well. I’d be interested to know what the thinking was behind these decisions.

If you’re a system tech, you probably are extremely skeptical of tuning presets like these. My view on this is more philosophical than technical:

  • If you’re a musician, and you just want to plug in and play, use whatever preset you think sounds the best. That’s clearly where QSC is going with these presets.

  • As an engineer, however, I feel that EQ’ing the entire system for a specific input is a big no-no. Each EQ has a job, and we don’t want to get the wires crossed. I use input EQ for inputs. I use loudspeaker EQ to manage the loudspeaker in the space. For more on this approach, see this article and this video by Dave Rat. Now, practically, if that’s all you have at your disposal, obviously you want to use it, but I try to adhere to strict EQ discipline whenever possible, which keeps things nice and organized, and pays off in spades on larger more complex systems.

The bigger and more practical issue is that I don’t want to use a preset unless I understand what it’s doing to my signal. This is the big distinction between the artistic and the technical. It’s perfectly acceptable in my view for an artist to be ignorant of what’s happening under the hood as long as they’re getting the desired results. Not so for an engineer.

Another good example of this is an “Enhancer” plugin or any sort of “magic black box” process. Lots of these exist. They all claim to make it sound “better” but don’t elaborate on how. If you’re a musician and you want to use it for artistic reasons because you like the way it sounds, go nuts. But as a system tech, I have full responsibility for the signal chain and everything in it, so if I can’t tell you what the device is doing to my signal, I’m not going to put it in the signal chain. (This isn’t about condemning certain products; it’s about educating myself about what those products do, and then making an informed decision as to whether or not it’s appropriate in the situation.)

In this specific application, the boxes in question are destined for use as low-profile monitors in a small (okay, tiny) club. Here’s how the two Stage Monitor EQ presets affect the response:

Yikes. I’m concerned about the gain reduction, and I’m not particularly excited about the 1k and 12k peaks either. But my primarily concern lies with the low end. These are small-format monitors, mostly for vocals, on a small, loud stage so we certainly don’t need all the LF response when there are large subwoofers a few feet away. I want to reduce the LF buildup from the floor coupling but not mangle the response completely. In general I’ll shoot for a highpass rolloff around 100 Hz. I’m not in love with either of the presets, so I figured I’d “roll my own.” Time to reset the DSP and start from scratch.

Looking at the 100 Hz and 125 Hz options for the onboard highpass filter, I didn’t really like either of them.

The 125 Hz setting (purple trace) rolls off too high to support the vocal fundamental, and the 100 Hz setting (light blue) is probably “close enough” but I’d rather split the difference. Additionally, I don’t like that bump around 600 Hz.

I was able to create this response using a combination of a lo-shelf (-2 dB @ 200 Hz) and a 100 Hz HPF along with a parametric cut at 200 Hz (-2 dB, Q = 0.7).

Now the LF is more of a mesa and less of a hump, and I’m still a comfortable ways down by 80 Hz. Another -2 dB filter at 800 (Q=0.5) tamed that midrange bump that would have sounded unpleasant with most vocal mics.

The install itself is going to have to happen in a very small time window because the club has scheduled events, so my strategy was to get things as close to dialed in as possible while still at the shop. Once I get into the room next week, I should be in the ballpark, only needing to adjust for the effects of the specific acoustic environment. A theme in common with my previous posts: note that we don’t need a ton of EQ to get results. The filters are wide and gentle. Nothing crazy here.

In conclusion, I would say that presets can be handy timesavers if they work for you. Whenever possible, before using one, I’d like to confirm for myself exactly what it’s doing.

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