- Emulations of expensive hardware are common, and although the most fuss tends to be made over the ones that imitate classics, there are plenty of lesser-known pieces of gear that have inspired great plug-ins as well. With Audified's U73b, there comes one more. The original was a 1950s broadcast compressor from West Germany designed to high specifications by Telefunken in response to standards set by the Institut für Rundfunktechnik, the research institute for broadcasting organizations. It was a vari-mu compressor, a type of valve compressor in which the ratio increases as the signal goes further above the threshold. It gained traction as a mastering compressor used immediately before cutting to vinyl, and it was a common feature on European lathes between 1960 and 1980. In making their re-creation, Audified took apart an original unit and built a software model based on the physical behaviour of each of its components.
Physical modelling can produce stout results, and the U73b has great strength of character. Its primary virtue is the way it brings things out in the mix. This is attributable to the modelling of the valves, which add harmonic distortion to a sound. The result is wonderfully detailed high-mids with lots of depth. It tends to clear sounds up, and if you use it on multiple tracks across a mix, it results in a mud-free, musical, vibrant sound. I found it particularly effective on tonal percussive elements such as high toms, where it gave them a resonating quality and let them cut through the mix a lot more. The original became the fastest tube compressor ever designed, and on snares, it's got an attack that's quick enough to be able to control the transient well. On the kind of bass sounds that have a full pluck and a long tail, like a bass guitar, it brought the sound out and controlled the bass regions. It sounded at home on tracks with long or continuous sounds, as well as on buses. This makes sense given that originally it would have been handling the drum, guitar and vocal stems of a band. On the drum bus, the auto release settings allow it to handle a percussive submix, where the sounds have various lengths of decay.
In its limiter mode, I found it to be a great tool for the master bus, where it imparted kaleidoscopic detail across the whole mix and glued it together. The soft knee in this mode made it not too aggressive. In particular, the lack of a bass rolloff made it possible to use it for this application. The rolloff in question, which you'll find on the U73b's compressor mode, was a feature of broadcast compressors, and it'll significantly cut the lower bass region, which makes it unsuitable for use on kicks with a low, 808-style tail, or very low basslines. Apparently, a future update will allow you to turn this off in compressor mode, and it'll be welcome. This is also partly why, when it's in compressor mode, elements often sound tighter, and mixes sound less muddy. This rolloff isn't there in this version, but apart from that, the compressor leads to radio mixes if used everywhere: bright, tight, and assertive.
In compressor mode, the threshold is set permanently low, another reason for its relative tightness. The ratio and attack are similarly hard-set. The action can be controlled using only an input gain knob and a release time knob, the latter of which has six discrete settings. The original didn't have an input gain control of its own, and I count this as one of several improvements that also include the ability to select a sidechain or various stereo sources for the gain reduction. The controls are the same in limiter mode, but the threshold and the ratio are both higher. This reduced feature set belies the compressor's sonic scope, and it takes more time than you'd expect to familiarise yourself with how it behaves. The release has three settings, from 300 milliseconds to 1.2 seconds. There are also three further auto-release settings, from 2.5 to 10 seconds, although these are presumably some kind of average, as the release will adapt to the source material on these settings. There's also a control for applying makeup gain.
The U73b is a special compressor. It can be a bit difficult to predict what's going to happen when you adjust it until you're used to it, and the effect is pronounced in terms of the tonal as well as the dynamic changes it imparts. On elements where it fits right, it can lend a magic touch, making them sound remarkably upfront and warm, like they've been through a professional mixing desk. The update that removes the rolloff in compressor mode will be a big improvement, but even until then it'll find plenty of use as a tool that's not only practical but unique.
Ratings:
Cost: 3.7
Versatility: 3.9
Sound: 4.5
Ease of use: 3.9