The Compex F760X is a faithful and approved recreation of the versatile compressor-limiter-expander from the late 1960's. The unit uses the same discrete transistors, with a single FET gain-reduction device in what is known as a 'vari-loss amplifier'.
Throughout the 1960s, '70s and '80s British manufacturers Audio & Design (Recording), now called Audio & Design Reading, enjoyed a phenomenal reputation for class-leading audio signal processors. Their now-classic F760X RS 'Compex' dates from the very late '60s. The F760X RS Compex reissue is built in America by a small company called Q2 Audio.
You can hear the Compex in action on countless hit records made in the '70s and '80s on both sides of the Atlantic, and it's most often praised for helping to create the huge drum sounds on records like Led Zeppelin's 'When the Levee Breaks'. The Compex does big, punchy drums extremely well thanks to its very fast attack and release time options, and it was routinely used on room mics and drum buses in many studios. Slower attack times can be used to make a wide range of instruments sound more dense and punchy too, but it can also provide subtle and transparent compression when needed - vocals and delicate percussive instruments like pianos and acoustic guitars are amongst the favorites.
The uber-fast peak limiter can sound a bit edgy — even brutal — with delicate sources, but can also be effective for adding character to transient-rich instruments. In general, I found I didn't use it very much because it often sounded a little heavy-handed, but it's useful to have (and is critical in setting the Compex up properly, of course). The compressor can be used as a limiter if necessary anyway, and the slower attack-time options employed avoid transient distortion, which can be prevalent in the limiter.
Using gentler compression ratios with modest amounts of gain reduction allows the Compex to provide sublime soft-knee bus compression for glueing a track together, and if the slowest attack time is used it retains nice crisp transient edges, sounding a little bit like parallel compression. The auto-release mode on the compressor is also an excellent feature. Auto-recovery is a common facility today, but it was an innovative feature in the 70s, and the two-stage recovery in the F760X RS works extremely well.
There were some different models of the 'Compex' available; one of these included a smaller console module named the F760-N. This version was built without the expander/gate, it later had an expander/gate added and was then known as the F760X-N. There is also a rare version called F760X-RS/T. One of the visible differences are the VU-meters, which got the brand "Audio & Design Recording LTD." and if you look on the rear, there you can see the type. The "T" stands for transformer, which are said to add harmonics to the sound.The "T" version was mainly used in broadcasting stations, mainly because of its SNR and headroom. ADR also built an F760 version for the Helios mixing consoles.
Classic FET based compression/peak limiting/gating, all available individually
Switchable compression ratios - 1:1, 2:1, 3:1, 5:1, 10:1, 20:1
Switchable compression threshold in 2dB steps
Switchable attack times - 250µs, 2.5ms, 25ms
Switchable release times ranging from 25ms to 3.2s plus "auto" setting
Peak limiting (100:1) with switchable 50µs pre-emphasis setting (useful for de-essing)
Expander/gate with 20dB of noise reduction
Compressor side-chain insert (can be internally modded to control the gate, instead)
Swiss-made ELMA™ rotary switches
The Gear Rack