The third and final type of gain reduction I will be covering, after FET and Opto, is Voltage-Controlled Amplifier (VCA). A VCA can be used to achieve gain reduction by using the input signal as the control voltage. Colouration as added to the audio signal, but not to the same degree that an Opto adds with both transformers and tubes (Haas, 2008).
The Distressor is primarily a VCA compressor with a fully analogue signal flow, but digitally controlled parameters. It has been designed to be an extremely versatile addition to an engineers rack, being able to emulate 1176 and LA-2A style compression, as well as everything in-between (Empirical Labs, 2015).
The Distressor is known for its heavy distortion, which is often used on kick and snare to tighten them up and make them hit harder. The graph above shows the flat frequency response of the Distressor, but heavy colouration from 40Hz and upwards.
The gain reduction graph shows the Distressor operating at its fastest attack and release times. The curve the VCA produces is much more aggressive than the ‘S’ curve of the FET. The energy is snapped back, when the threshold is fallen underneath, like a rubber band being released. The FET had a much more designed two stage release phase to create a dramatic hold and push of energy.
One particularly special feature of the Distressor is it’s completely different gain reduction circuit, to perform Opto compression by switching from VCA to an Optical Photocell. This allows true Opto compression, by switching to the 10:1 (Opto) ratio. The graph above illustrates how well the Distressor can emulate this style of compression.
The attack phase matches the static 10ms attack of the OneLA, on both transient and sustained material. Whereas the release phase is affected by the intensity and duration of the input material (White, 1997).
Empirical Labs. (2015). Empirical Labs Distressor – Digitally Controlled Analog Knee Compressor. Empiricallabs.com. [Online]. Available at: http://www.empiricallabs.com/distressor.html [Accessed: 30 March 2016].
Haas, W. (2008). The SOS Guide To Mix Compression. Soundonsound.com. [Online]. Available at: https://www.soundonsound.com/sos/may08/articles/mixcompression.htm [Accessed: 30 March 2016].
White, P. (1997). Empirical Labs Distressor. Soundonsound.com. [Online]. Available at: http://www.soundonsound.com/sos/1997_articles/dec97/empiricaldistress.html [Accessed: 30 March 2016].