You are here

IGS Audio Zen

Dual-channel Zener Compressor/Limiter By JG Harding
Published July 2022

IGS Audio Zen

Diode‑based compressors can be delightful but also rather noisy. True to its name, the Zen promises a more peaceful approach...

Polish company IGS, the vehicle of ‘mad scientist’ designer Igor Sobczyk, are fast becoming one of the most interesting hardware manufacturers out there. Their range includes Igor’s interpretation of various classic bits of studio outboard gear, including several types of compressor, as well as more original designs such as their Tilt N Bands equaliser. I have one of their Tubecore Mastering Edition compressors, and it’s well built, sounds great and finds its way onto plenty of my work. Based on my experience of that and the other IGS toys I’ve tried over the years, I trust this company to do a good job.

IGS have offered their V8 diode‑bridge compressors for a while now, but more recently they released the Zen. Whereas the V8s seem to find their inspiration in the classic Neve diode‑bridge designs, the Zen instead takes the Abbey Road EMI TG12413 limiter as its starting point. The TG12413 is one of three designs famously developed for Abbey Road that employ Zener‑diode limiters; the other two are the RS168 limiter and the TG12345 console channel. Its two modes (compress and limit) were reportedly developed to offer engineers a choice between the Fairchild 660 (limiter) and Altec 436 (compressor) behaviours with which they were familiar. Sadly, I’m not based at Abbey Road (I do have a scar on my arm from one of their REDD.37s but that’s a story for another day — for now let’s just say the definition of ‘portable’ has changed over the years!). However, I do own a TG12413 clone, based on the original circuit diagrams but with some custom modifications, and given my previous experiences with IGS I was really keen to see how this and the Zen would compare.

Diode In Your Arms Tonight

Before I dive into the pros and cons of the Zen itself, some general context about analogue compressors might be useful. There are various ways to design the gain‑reduction stage of an analogue compressor and each imposes certain characteristics on the source, in terms not only the gain reduction itself but also of noise levels and harmonic distortion. VCA, FET, diode‑bridge, valve (or Vari Mu, to borrow Manley’s trademark term) and optical are probably the most popular types, and the order in which I just listed them is a good rule of thumb when it comes to judging how fast they’re able to clamp down on a transient (the list runs from the fastest acting to the slowest). Diode‑based limiters and compressors sit somewhere in the middle: while they can be set up to act more slowly, they generally sound pretty fast to my ears, even if they can’t act quite as quickly as VCA or FET types can.

In terms of colourful harmonic distortion, VCA and optical circuits tend to sound pretty neutral/clean — there are characterful VCA and optical devices, but that’s usually down to things like transformers, amp stages or dedicated distortion circuits. FET‑based designs tend inherently to be more colourful. Again, a diode‑bridge compressor sits somewhere in the middle.

Compared with other approaches, then, it’s fair to say that a diode‑based compressor‑limiter is capable of reasonably speedy dynamic control while adding a pleasant touch of colour. One factor that affects the behaviour and sonic character of a diode‑bridge compressor is the type of diode used, and Zener‑based designs have a distinct sound.

A potential problem with almost all diode‑bridge designs has been noise. The audio signal must be attenuated so it hits the desired section of the diode’s non‑linear ‘transfer curve’ and must be boosted back up again, along with the noise floor. This can mean more noise than you’d like if pushing the compressor hard and applying makeup gain.

Zen & The Art Of...

You are reading one of the locked Subscriber-only articles from our latest 5 issues.

You've read some of this article for free, so to continue reading...

  • Log in - if you have a Subscription you bought from SOS.
  • Buy & Download this Single Article in PDF format £1.00 GBP$1.49 USD
    For less than the price of a coffee, buy now and immediately download to your computer or smartphone.
  • Buy & Download the Full Issue PDF 
    Our 'full SOS magazine' for smartphone/tablet/computer. More info...
  • Buy a DIGITAL subscription (or Print + Digital)
    Instantly unlock ALL premium web articles! Visit our ShopStore.

Claim your FREE 170-page digital publication
from the makers of Sound On SoundCLICK HERE