U73b Compressor Vintage Sound Now Available as an AAX Plug-in by Audified

By in Music Creation, Pro Mixing

It is not very well known, that the company that created the world’s first dynamic processor was Telefunken in Germany. Their U3 compressors found practical application during the Olympic Games in Berlin in 1936.


The History

The fast pace of German industry in the 1930s helped to nurture a number of technology companies. At the beginning of the 40s, a new generation of compressors was introduced, the U13 by Telefunken was the first dynamics processor to use the diode bridge. After the war, work on the compressors of this type was taken on by Rhode und Schwarz, introducing the U23 model in 1954, widely used in broadcasting stations and the first recording studios.

In terms of design and sound it is similar to the American Fairchild 660 (after the war, the roles were reversed and the Americans became the technologically dominant designers). Although U23 sounded great, it did not meet the exacting standards of the IRT (Institut für Rundfunktechnik GmbH) and Telefunken was commissioned to carry out its successor. After three years of work, the Telefunken/AEG U73 appeared in early 60s. It was a tube compressor built in a configuration with variable transconductance (variable μ), offering theoretical compression ratio of 100:1 and the shortest reaction times in the history of tube processors thanks to the innovative feed-forward mode. U73 was produced by TAB, the owner of the license for the device, mainly for German-language broadcasting market. Quite a few U73s were also used in recording studios throughout Europe, where they found their place in every practically every vinyl record mastering room, especially the U73b version.

Original U73b Valve Compressor

The Rebirth

Decades after the U73b was invented, created and used, it was discovered by Czech artist and producer Boris Carloff, who has been a great influence on the development at Audified.


“I’m a long time fan of German broadcast technique and of course German and Austrian mics,” says Boris. “I was quite surprised that nobody really knew about the Fairchild 670 predecessor – the Telefunken U73b. I had a chance to have one in my studio and I was amazed how great it sounds. U73b has this rich velvet sound which I liked even more than the sound of its more famous colleague. So I came up with an idea that it would be really useful to make it as a plug-in because U73b is a very rare item.”


It took several months to get from the first idea to functional plug-in module. The Audified development team simulated every single circuit of the original device and every minute detail. When the plug-in module was tuned to perfection (under Boris’ supervision) another artist, Bjorn Thorsrud, the producer known for his work with the Smashing Pumpkins, Shania Twain, Whitesnake and others, teamed up with Audified. It was  Bjorn and Boris together that created a set of presets that help you get the best out of U73b Compressor.

Is it the original?

People often ask whether some devices are just inspired by the real model or whether they are real. Well, U73b is as real as gets. Audified kept the circuit exactly as it was originally designed and only added input and output gain (before and right after compressor circuit) to help with proper adjustment of the compression. The plug-in effect has also been supplemented with a VU meter and selectable side-chaining. When first released, users pointed to an interesting fact, U73b is a vintage device and as such it may not meet present mastering demands.


“We added a bass management button that simply switches between original sound and desired modern sound (without low frequencies bypass),” says lead programmer Jarda Macak. “Now U73b Compressor plug-in is better suited for mastering and processing instruments with fat low end. The original device, and our first model, also shifted phase. This feature is pointless, so we removed it.”

U73b AAX Plug-in


The name Audified may seem new to you. But the company has been together for more than 15 years. Formerly D-Sound and Audiffex is now renamed to Audified. Audified is the premier brand of privately-owned Boskovice-based DISK Multimedia, s.r.o. in the Czech Republic, created to develop specialized audio applications, as well as handling the company’s high-end hardware product portfolio.

Pioneering the development of audio applications for live (real-time) performance, as well as developing the first audio effects plug-ins for Apple’s Mac OS X (now known as Audiffex Pedals), the company also created some of the first plug-ins for PowerCore, TC Electronic’s hardware-accelerated DSP platform.

Buy Now on the Avid Store

Now Available on the Avid Store

Get some U73b compression in your mix. Available today in both AAX Native and AudioSuite plug-ins from the Avid Store.

Marketing Director and Project Manager at Audified. In my past life I worked as the Czech MI magazine deputy editor-in-chief, computer magazines editor and reviewer. I gained a lot of positive Pro Tools experience when working as a director of promotion trailers in Czech Barrandov TV Channel.