By Samuel--OSullivan • March 8, 2012 This article is provided by the Pro Audio Files. Bus compression is certainly not a new concept, however, it is an effective and reliable engineering tool and its basic principles are vital considering you are affecting multiple voices. When approaching bus compression, there are two essential tools at your fingertips: Attack and Release – these two tools, when properly utilized, will have the ultimate say in the outcome of your efforts. The attack and release functions of a compressor will tell its detector how to react to signal that passes through. An effective use of attack and release will essentially allow you to make conscious envelope changes to the signal rising above the threshold at the detector. This brings about the main philosophical concept behind compression, which is to shape the signal, rather than merely restrict its dynamic range (dynamic restriction is part of shaping the signal, not the end purpose). The attack and release controls are what really provide the push and pull effects of compression. With this in mind, I have provided examples of effective and ineffective bus compression, focusing on attack and release settings, for a few simple approaches. All of the following audio passed through the same compressor with the same settings (beside attack and release) and a ratio of 1.5:1 with an average gain reduction of 4 dB. Original Track (No Bus Compression): Listen ———————————————————————— Effective Transient Compression: Listen Attack Setting: 8.5 ms Release Setting: 7.5 ms Why? – The quick attack captures the transient before it reaches it’s fullest point, and the release lets go during the decay, allowing the transient to be tamed while the rest of the signal passes through unchanged. The push and pull is effectively centered over the rise and fall of the transient, making its response symmetrical and maintaining the integrity of the attack and decay slopes. ———————————————————————— Ineffective Transient Compression: Listen Attack Setting: 16.0 ms Release Setting: 32.0 ms Why? – The attack setting coincides with the peak of the transient and the release lets go during the sustain of the signal, smearing the punch of the transient and causing a noticeable dynamic hiccup after the decay of the transient. This is an arhythmic push and pull. ———————————————————————— Effective Sustain Compression: Listen Attack Setting: 32.0 ms Release Setting: 10.0 ms Why? – The attack captures the signal during the sustain causing the transient to be unaffected, while the release lets go quickly enough as to not overlap with the following transient. In other words, only the sustain of the signal is affected. The push and pull is centered over the sustain, bringing it to the forefront while maintaining the integrity of the sustain slope. ———————————————————————— Ineffective Sustain Compression: Listen Attack Setting: 83.0 ms Release Setting: 51.0 ms Why? – The attack grabs the signal well after the beginning of the sustain causing an unnatural sounding sustain, while the release overlaps the following transient, causing a blur that does not rhythmically coincide with the music. This is also an arhythmic push and pull. ———————————————————————— Effective Combined Compression (Transient and Sustain): Listen Attack Setting: 5.5 ms Release Setting: 97.0 ms Why? – The attack grabs the signal before the transient is at it’s peak, and holds for the duration of the sustains, letting go before the following transient. In other words, these settings are rhythmically harmonious with the music. The push and pull between transient and sustain is achieved. ———————————————————————— Ineffective Combined Compression (Transient and Sustain): Listen Attack Setting: 4.0 ms Release Setting: 620.0 ms Why? – The attack is okay, but approaching a dangerously fast zone where if it were any quicker, the attack of the signals envelope would lose most of it’s slope, causing the transient to sound unnatural or “over-compressed.” Additionally, the release setting lasts way too long, making all settings irrelevant. This is all push and no pull. Samuel O’Sullivan has been playing various instruments and composing within the bounds and mixtures of multiple genres for more than 10 years. He first established as a drummer/percussionist, has made his mark as a guitarist, vocalist, pianist, violinist, composer, and recording engineer. In addition to producing albums for various bands, O’Sullivan produces his own music under the name “A Mess of a Mind”. 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