Tube Compressors

Tube compressors are compressors that rely on tubes to tame the dynamic range of your audio signal. But before delving into an explanation, we must first understand the involvement of tubes themselves.

The Tubes in Tube Compressors

The main job of tubes in audio equipment is to amplify electricity. The first vacuum tubes were used in electronic amplifiers long before transistors were launched to the public. Vacuum tubes have a peculiar sound when used as audio amps and they tend to smooth out rough sounds.

Tubes are convencional in many devices, such as mics, guitar amps and equalizers. Someone needs to warm them up in order for them to work efficiently on hardware devices. This warming up takes time since they have to reach a specific temperature to become stable. Before they reach this stability level, the tube-based audio processing devices might have fluctuating outputs that can distort the overall sound. Tubes are extremely fragile when reaching high temperatures, so it is essential to let them cool down after each performance.

Tube Compressors: How Do They Work?

In the beginning, tube-based compressors, also known as valve-based compressors, were the only alternative of machine-modifying gain. They originally worked with a level detector circuit that sent the voltage directly to the tube. When they receive the voltage, it drives the gain of the tube.

In turn, when the gain changes by the level detector circuit, there is a reaction time within the tube. There might be ups and downs within the gain, but they are never immediate. Because of this, the tube-based compressors have peculiar attack and release time properties. In addition, the rate at which the gain increases or decreases has a direct impact over the quality of the compression effect.

Tubes are common to add warmth to drums, vocals, and basses. The warmth effect occurs in the final gain circuitry of the compressor and it’s the result of the movement of electrons. When talking about valves, this effect happens at exactly twice the frequency of the amplified signal. Although it presents a mild distortion, the human ear finds it appealing.

Some Examples

Examples of these are Fairchild’s and Altec’s compressors. Nowadays, many designs created by Manley, such as vari-mu, use a tube instead of a transistor, which results in a smoother, creamier, and more organic sound. The musical and charming distortion generated by the tube-based gain state is part of the tube-compressor sound.