Tips for Effective Buss Compression

➥ Learn how to control shape, tone and dynamics with compression

Buss 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 buss 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 buss 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 (with no buss compression):

Effective Transient Compression:

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:

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:

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:

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):

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):

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.

Do you use buss compression when you mix? Why or why not?

Here’s a tutorial from Matthew Weiss on using Slate Digital’s FG-Grey on the stereo mix buss to enhance the sense of groove, a shootout from Ian Vargo comparing the SSL Duality with the Waves G-Channel Buss Compressor plugin, and a walkthrough of David Glenn’s two-buss signal chain.

Sam O'Sullivan

Sam O'Sullivan

Samuel O'Sullivan has been playing various instruments and composing within the bounds and mixtures of multiple genres for more than 10 years. Samuel, 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, Samuel produces his own music under the name 'A Mess of a Mind'.
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  • http://www.kawentzmann.de Kawentzmann

    That is quite useful. Thanks! I hardly ever used a quick attack setting before, always wanting to preserve the peaks to hit softclipping down the line. But the sculpted transients really sound beautiful. I must say that I really dig the tune too, it sounds familiar, but I can put a name on it.

    • http://samuelosullivan.com Sam O’Sullivan

      Thanks for the feedback! I appreciate it. The song is actually one of mine. I recorded it a couple years ago to 2″ tape using only ribbon microphones run through tube gear. It was an experiment in recreating vintage tones with modern technology. If you want the name, I call it “Fifties Tune.” (Should be easy to remember)

  • Laoen

    Hi Sam, great article, Thanks!

    One question though, in the section “effective sustain compression” you say that the compression is centered over the sustain portion of the signal and is bringing it to the forefront… So, I understand the that attack and release settings have the compressor action centered over the sustain, but how is it bringing the sustain forward? Shouldn’t the compression be be reducing the level whenever it is triggered?

    Thanks.

    • http://samuelosullivan.com/ Sam O’Sullivan

      Good Question. The subtleties of sonic perception are key here.

      What you say about the sustain being the only affected part of the signal is true. The important part about this approach is that it creates a complete separation between the unaffected transient and the fully affected sustain.

      In allowing the transient to pass unaffected, it maintains all of its energetic integrity and in affecting the sustain completely, its slope remains closer to static than its normal (natural) roll-off. This gives the listener the perception of the sustain acting unnaturally while the transient appears completely natural, and consequently, the sustain becomes perceptually distinguishable from the transient due to this “irregularity.”

      Now, if the attack setting allowed the transient to be affected by compression (by making it quicker), it would have the opposite effect and would make the transient and sustain more similar in their irregular attributes, thus not highlighting the sustain as special.

      Auditory psychology can be extremely fascinating, and a whole new mixing realm to explore: instead of thinking of buttons and knobs and radio station limiters, mixing toward specific psychological auditory functions. I believe it can be a step closer to connecting with the audience in a way an artist truly wishes.

  • http://www.bourkel.com Charel Bourkel

    Hi, very nice post. I use a buss compressor on nearly all of my mixes, except for classical music. It usually does only between 1 and 3dB GR. But I never used attack settings, that were that short, neither this long release settings. I’ll try those on the next occasion.

  • tony

    It’s really helpful when an article is laid out like this. Seems like you know your stuff

  • Zangief

    Dammit, I cannot hear the difference between any of these.
    Well, I am listening on $10 headphones, so I’ll hope that’s the reason for now…

    Thanks for the valuable post. I’ll have to study it more later when I’ve got access to good monitors!

  • Josh Lewis

    I would also add that part of the shaping process might include blending of dry signal back in with processed a la time based. Another distinction: which buss? Mix buss, drum or other stem busses. A B C main console buss a la m. brauer. Compression, can be used for transparent dynamic control, reshaping sound envelopes, and everything in between. If it is indeed mix buss that you are talking about, some combination of very quick limiting, and well timed low ratio compression tends to work well. Finally, do you want to add “vibe” or any of the other intangibles available with the gain makeup circuits? For a great overvue of compression please do visit our site http://www.littlefishaudio.com

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