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Double Compression Technique

Updated: Dec 19, 2021

What is double compression technique?

In some cases, an audio source may need more than one compressor to maintain a good dynamic balance.

The double compression technique consists of applying two or more compressors to control the differences in dynamics in an audio signal.

Most of the time we start with a fast compressor, called a "sport" or fast compression. We use a VCA (Voltage Controlled Amplifier) compressor which allows fast compression with more versatile parameter adjustment (ie. DBX 160, SSL G bus, API 2500 etc.). Also considered the most transparent compressor (depending on the model). Or you can use a FET (Field Effect Transistor) type compressor, the compression principle is applied through transistors that can attenuate or amplify a signal.

This same component is able to bring some harmonic distortion which allows it to add color to the signal. FET compressors are fast and bring color to the sound (ie. Urei 1176 etc.).

The purpose of the "sport" compression is to reduce the highest amplitudes/transients to balance with the lowest amplitudes.

The second compressor will be slower to trigger the compression, allowing it to act as a tool to adjust the levels (a "leveler"). For this compression we would use an Opto (optical) compressor, which uses a photosensitive resistor to apply the compression. Most Opto compressors will have a tube amplification circuit, which brings harmonic distortion to the signal and thus brings color to the sound (ie. LA2A, Tubetech CL1B, LA3A etc.).

The purpose of this compression is to let the strongest amplitudes/transients pass through and adjust the levels with the other amplitudes.

This technique allows to control the amplitude changes of a signal, as well as to normalize the levels to be able to put a sound source in the first plan of the mix and to have a stable level all along the song.

🙌 It’s possible to use a VCA as a sport compressor and a FET as a second compressor (with a slower attack and a faster release) which allows to add color to the signal and add harmonic distortion. 🙌

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