Getting Hands-On with the Manley Massive Passive EQs

The Manley Massive Passive EQ Powered Plug-In represents UA’s most complex hardware emulation to date. It is also the most CPU-intensive plug-in in the UA library, and for good reason: The behavior of the transformers and inductors, called hysteresis, was modeled, as well as the tube stage behavior. In this article, I’ll talk about the challenges UA faced while modeling this iconic piece of hardware. And then you can hear the results in the accompanying video.

When UA first decided to model the Massive Passive EQ, we thought it would be challenging; but we’d modeled plenty of EQs before, so we were fairly confident we could nail it. But as we started looking at schematics and measuring the output, we realized that there was a lot going on inside. To put it simply, this was not going to be a straightforward EQ modeling job. The big challenge was modeling the hysteresis present in the transformers (also known as inductors, or chokes) that are part of the frequency-selection circuitry. But this challenge was worth it, because this is a big part of the Massive Passive sound.

In the Massive Passive EQ hardware, there are quite a few inductors in the circuit that not only can saturate, but can also display hysteresis. Since hysteresis is a complex form of non-linearity, it can’t be represented with a static model, like dynamic convolution. One of the nice features of hysteresis is that you can end up with a pretty consistent amount of distortion over a really wide dynamic range.

Hysteresis can happen in such a way that produces a really broad dynamic range over which there is a moderate amount of distortion. This turned out to be precisely the case with the Manley Massive Passive EQ. It has a pretty broad range of what we call “warmth.” It is basically broadband, non-linear behavior, a musical source of mild distortion. We modeled this hysteresis, as well as the effects of the transformers saturating. The saturation of the transformer is more audible than the hysteresis, and combined it makes for unique sound not found in any other EQ.

By contrast, the tube stages of the Manley Massive Passive EQ were actually pretty clean, and didn’t produce much distortion at all. This tube stage still had some non-linear behavior, which we modeled, but it is nowhere near as evident as the sound of the transformer hysteresis. As you'll hear in the video, we believe the results of this extensive modeling project were worth the effort.

— Dave Crane