Aside from the great equalizers that you can find in their collection like SonEQ 2 or Burnley 73, Sonimus also has a compression gem among its treasures. There have been great reviews about it and many engineers use it regularly in their mixes because of its warmth, flexibility, and glue effect. We are talking about Tuco — but what is the magic behind it and why is it such a musical compressor? Let’s find out!

Tuco is a digital emulation of a vari-mu compressor with feedback topology. A vari-mu (or variable gain) compressor is a type of analogue compressor that uses vacuum tubes (valves) as its main element for gain reduction. 

Vari-Mu Compression

When most people think about tubes they think about guitar amplifiers, but in reality, these electronic devices have been used for all kinds of dynamic applications, including audio compression. 

Compressors in general depend on two parts for them to work: The gain reduction circuit and the sidechain circuit. The gain control section, as its name suggests, manages how much the audio is being compressed. The sidechain, on the other hand, determines the peak value of the audio signal coming into the compressor. Simply put, when this peak value goes over the threshold of the compressor, the sidechain feeds the gain control section causing the desired compression of the audio.

In a vari-mu compressor, the vacuum tube carries out the gain reduction while a combination of diodes and capacitors forms the peak detector circuit. There can be other valves in the circuitry of the compressor, like the output section for amplifying the signal, but as we mentioned before, for these kinds of compressors there will be a tube as the main element of the gain reduction circuit.

Just as it happens in the G-buss compressor, the peak detection in the sidechain is located after the gain reduction circuitry. This topology of the design is what is called feedback compression, and in the case of a vari-mu compressor, it causes the signal to continuously adjust the bias of the valve to modify the gain.

Due to the nature of the tube itself, the type of compression occurring is a soft-knee compression. This means that the audio is compressed gradually as the signal volume gets closer to the threshold value, and the ratio of the compressor also increases as the signal gets louder over the threshold value. That is why a vari-mu compressor is also known as a program-dependent compressor.

In addition to all of this, the inherent addition of harmonic distortion from the valve itself gives the audio being processed that characteristic tube warmth which in a way also affects the peak detection and side-chain circuitry due to the feedback topology.

The result is a smooth and musical compression that works wonders as a bus compressor and or mastering tool.

Tuco

Sonimus has been able to emulate all these characteristics and turn them into a great sounding and versatile plugin with extra features for the modern producer. 

Aside from its two compression modes with two different attack settings, Tuco also provides one mono and three stereo behaviors (stereo vintage, modern and dual mono) that change how the side-chain detector and signal processing respond to stereo input signals.

Tuco also has a setting section with a Mix knob for quick parallel compression setup, and a Drive knob to add extra analogue saturation to the signal. In between these two, users can find a screw-like control to adjust the high pass filter of the side chain circuit, to allow the low end to pass through without being picked up by the peak detector section. This is very helpful when using Tuco as a master bus compressor keeping your track punchy and fat. 

Finally, the ability to save your favorite settings and A/B them while you tweak the parameters puts the icing on the cake for this great analog-sounding compressor.

Did you know about how vari-mu compressors work? How do you use Tuco? Would you like to see other features in future compressors? Let us know in the comments and subscribe to the newsletter to get notified with the latest videos and posts of our blog.