New Software Review: Chandler Limited Zener Limiter by Universal Audio

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In addition to Chandler Limited’s unmistakable sonic footprint (evident in both the hardware and software versions of the Zener Limiter), the plugin offers added features such as the ability to use it in dual mono, stereo, and Mid/Side mode.

I have had many chances to try out and use gear from Chandler Limited, either in plugin form or with pieces of analog hardware as a guest engineer in commercial studios. I can say without reservation that everything they make is of the highest quality, in terms of circuit design and build. In addition, everything they make does something unique and interesting.

After my recent review of the Curve Bender EQ, I was excited to give the Chandler Limited Zener Limiter a try and run it through its paces. Since I already own a UAD QUAD Satellite, the installation was easy and I was quickly on my way.


Since I had never used the Zener Limiter before, I inserted it on a track, opened the plugin and took a look around. It has all the usual controls one would expect to see: Input, Output, three different Comp/Limit settings, a sidechain filter, plus of course, Attack and Release controls. It also has a switch labeled “Input Gain” (offering selections for “High” and “Low”) and another switch that toggles between “THD” and “Limit.” There are channel bypass buttons, a Mid/Side mode selector and a “Link Channels” button as well.

While most of it seemed like every other limiter, there were a few things that I felt needed some clarification. I could just run some signal through it and play around with the controls to see what it does (and I did), but I felt that a deeper understanding was warranted to really get the most out of this box. Time to consult the manual!

As with everything Chandler Limited creates, there’s a bit of history involved in this offering. The Zener Limiter is based on some EMI limiter designs, specifically the RS168 and the later version of the limiter that was part of the TG 12345 console channel strip. The Chandler Limited version has been updated for modern use, with the inclusion of some new features that contribute to its flexibility while making it attractive to modern music makers.

A few of the controls need some explanation due to the uniqueness of the compressor. It is worth noting that all of the information in the user manual is pertinent to the hardware version, but for the most part, the plugin version behaves and reacts the same.

The Input Gain switch changes the gain and impedance simultaneously. When set to “Low,” the input impedance is 1200 ohms and the signal level is close to unity gain; when set to “High,” the impedance is lowered to 300 ohms and there is an additional 12dB of gain.

The Input control is an audio taper control, so it will not behave as you might expect if it were a linear taper control. Since the Zener Limiter is a fixed-threshold compressor, the amount of compression is set by how hard you drive the input, rather than having an independent threshold control. This is the same as an LA-2A and an 1176, so most users will be familiar with this concept.

The “THD” toggle switch disengages the limiter’s threshold but still runs the signal through the entire audio path, including the sidechain. This adds a smooth distortion and a high frequency bump due to the discrete amplifiers and the zener diode limiting circuit. The amount of distortion depends on how hard you drive the circuit. The manual states that it takes a signal and “gradually triangulates it as you increase the Input control, however importantly, it does not clip the signal in any way.”

[The hardware manual offered something interesting with regards to the “THD” mode and how you drive it. If you boost the Input control all the way up and feed it a unity gain signal, you can drive the unit to 2% distortion. However, if you increase the input level in front of the Zener Limiter to +4dB or +5dB, you can drive it to 5% distortion which (as the manual states) is “many, many times that of tape and without distortion.” In other words, you can drive this unit and get some cool sounding harmonic distortion, which can gently tame transients while increasing the RMS level of the signal. Very cool!]

Understanding the “Comp 1/Comp 2/Limit” switch is pivotal in achieving the tone you want from the Zener Limiter. “Comp 1” has a ratio of 2:1 but emulates the response of the Altec 436/RS compressor, which was subsequently modified by EMI. This setting has the slowest time constants of the three available settings. “Limit” has much faster response times and is much like a Fairchild 660. “Comp 2” is designed to be somewhere in between the two other settings, which further adds to the limiter’s flexibility.

The Attack and Release controls are switches with 11 and 21 positions, respectively. The values for each are dependent on the Comp/Limit control’s setting, but in general are fastest in the “Limit” setting and slowest on the “Comp 1” setting. (If you want to know the attack and release values, you can consult the online manual here.)

The labeling on the faceplate is notable in that some of the values are labeled in white whereas others are labeled in yellow. Specifically, the release values in white with parenthesis are the original unit’s values, while the yellow labels are the added values that Chandler Limited included in their design. This color convention is true for the Attack and Comp/Limit controls as well. This is important to note only if you wish to use the limiter as it was originally designed by EMI. I’m sure for some this is helpful when emulating a particular kind of sound, but as with anything, the addition of more values can only be seen as a benefit.

One unique feature that the plugin version offers is that the limiter can be used in dual mono, stereo, or Mid/Side mode. For dealing with stereo sources, Mid/Side operation gives you more flexibility and can be a life-saver when mastering stereo mixes with too much or too little vocal. It certainly adds to the appeal of this plugin.

In Use

The first thing I usually check when using a new plugin is what kind of CPU hit my computer takes when I drop it on a track. The Zener Limiter uses 6% on my UAD QUAD Satellite in mono and 10% in stereo. This is a pretty significant amount of CPU to allocate to one compressor, but if I use it in only critical situations, it wouldn’t cause a problem at all. This is a pretty unique sounding compressor and is not necessarily perfectly suited for all sorts of tasks, so I can’t see this restriction being an issue for anyone who purchases it.

I have to admit that my first impression of this limiter left me scratching my head a bit—not because of how it sounded, necessarily, but because the gain structure is a little bit odd. Being a fixed-threshold compressor means that the only way to increase or reduce the amount of compression is by turning the input up or down. In theory, this is pretty simple. In practice however, I found that it was hard to get subtle amounts of compression on louder, steady-state sources (like a bass guitar or a full mix). When I would set the gain switch to “Low,” the amount of compression was greatly reduced, but I couldn’t always make up the gain by boosting the output all the way.

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  • Echobeach

    Very helpful review, Mike. Thx!