Practical & Effective Compression Use

In my personal opinion, one of the most over-used processing techniques in all of sound recording and production is compression.  Somehow, it’s been embedded in every young engineer’s mind that in order to get giant sounds, one needs compression, especially on drums.  I couldn’t disagree more.  In virtually all of the music I’ve produced, from the Flaming Lips “Slow Nerve Action” drums, to the giant guitars and drums of Hum and Flickerstick, to the often deeply-layered three-dimensional sounds of Mercury Rev, I have never used a single compressor on any of the drum tracks, and have limited my use of compressors, as a general rule of thumb, to vocals and bass guitars.

Down Mean Louder?

Let’s think about what compression does in the simplest of terms:  Compression lowers loud sounds and raises quiet sounds.

That’s all that compressors do, from the simplest analog compressors, to the multi-band, low-latency, ultra-sleek mastering compressors by elite plugin companies like Waves.  They simply perform these functions in various ways, such as “hard-limiting” the loud sounds, “looking ahead” to remove transients, splitting the sounds into multiple bands and adding compression to individual bands of a sound, or shaping how the compression is applied, such as “soft-knee” or “hard-knee” compression.

Inevitably, any sound that was recorded in a space, carries with it some natural reverb.  Unless a recording was made in an anechoic chamber, no matter how close one is to a microphone, no matter how narrow the pickup pattern of the microphone is, there will be ambient sound that gets picked up by the microphone.  If we apply a simple compressor to this sound, one of the most noticeable changes to the sound, is that the background ambiance, the natural reverb is amplified and blended with the “dry” signal.

This simple change in acoustics, tells our brains that the sound is larger.  Now, understand that is just a general rule of thumb, and isn’t without its many exceptions.  But it gives us a place to start, to ease our understanding of compression as an effective tool for music production.

Smooth That Sound

Another key aspect of compressors is their ability to “even out” tracks (or entire songs), that have a wide dynamic range.  Dynamic range is simply the range of space between the quietest sound on a track (typically the spaces between the notes) and the loudest sound (typically a transient).  As an example, on a bass guitar track, the loudest sound typically happens a number of milliseconds after the initial string is plucked, when the string reaches its fullest resonance.  If a pick is being used, sometimes the pick itself creates a very loud spike (or transient), but it’s not actually the sound of the bass guitar causing that spike.  Just before another note is struck, or when the bass isn’t playing a note at all; that would be the quietest sound recorded.

Especially with transient sounds (like a pick striking a string, a drumstick hitting the metal rim of a snare, or the worst offender; shakers), they can greatly reduce the volume at which you can record a track.  Try to record a tambourine or a shaker; you will notice that you have to noticeably reduce the input volume for that instrument.  That’s because the transients, typically outside our range of hearing, are incredibly large, causing spikes in the recording levels, often pegging the meters in the red.  When recording digitally, it’s critical important not to trigger the “O/L” light, as that will result in digital distortion; a very non-musical type of distortion.

Thankfully, with such high resolution recording at virtually every musician’s fingertips (24-bit is plenty high), sounds with loud transients can safely be recorded at lower input levels, without any noticeable degradation of sound.  Because of this, I rarely advise placing a compressor on any sound BEFORE it gets recorded to a track.

When to Attack & Release?

One of the questions I get most-often is in relation to the attack and release times on a compressor.  I think most engineers wish there was some sort of chart that clearly tells us what to set attack and release times at for our compressors.  I’ve provided a simple reference below, but it’s only a reference; the best tool for measuring attack ad release times is your ears.  If we stop looking at ratios and milliseconds, and simply close our eyes with our fingers on one of the compressor’s knobs, it’s surprising how accurately we can set the attack times for the most musical sounding compression.

  • DRUMS (KICK): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • DRUMS (SNARE): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • DRUMS (KIT): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • GUITAR (BASS): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • GUITAR (ELECTRIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • GUITAR (ACOUSTIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • BRASS: Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • KEYS (ACOUSTIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • KEYS (SYNTHESIZERS): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • STRINGS (VIOLINS): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • STRINGS (CELLOS): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • VOCALS (MALE OR FEMALE): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB
  • STEREO MIX: Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

Obviously, this is just a general guide to give you a starting point.  It will not always apply, and sometimes the most musical results happen by NOT following any of the rules.  As my greatest audio production teacher said; “Learn the rules, so you know how to break them.”  I didn’t realize how sage that advice would be as I began my career in music production.

In-Depth Starting Points

This entire section is simply that; a starting point, a general rule to get you to start thinking about sounds and times in terms of milliseconds.  As is always my mantra; thinking about how you want to shape a sound, thinking about what the shape of that sound is, looking at an actual waveform of that sound, and simply LISTENING to that sound is the most powerful set of tools you have in finding that perfect sweet spot in any sound.  So, use this more as a guide to thinking about sound, and not as a chart that you will pull out during a recording session to know what settings to put your compressor at.  Seriously.

DRUMS:  Drums will always be my favorite topic, and I think it’s easy to hear how much I love drums in most of my productions.  Virtually every non-live recording I’ve made starts out with a single scratch guitar and scratch vocal.

GUITAR (BASS): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

GUITAR (ELECTRIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

GUITAR (ACOUSTIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

KEYS (ACOUSTIC): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

KEYS (SYNTHESIZER): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

BRASS: Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

STRINGS (VIOLIN): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

STRINGS (CELLO): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

VOCALS (MALE OR FEMALE): Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

ENTIRE MIX: Soft-knee, 3:1-6:1, Attack time 2-10ms, Release time 0.3-0.5 ms, Volume reduction 5 to 7 dB

Hopefully by now, you’ve got a much clearer understanding of compression.  There’s lots more that could be discussed, such as hard-limiting, comparisons between compressors, analog or digital representations of analog compressors, and so on.  But this is meant to be an absolute basic starting point for you.

Ears Are Always King

Finally, despite the plethora of compressors at our fingertips; from stomp pedals, to classic tubes, to the most complex digital multi-band limiters, they’re all performing the exact same function.  Because of this, if you think of a compressor as a black box that “lowers loud sounds and raises quiet sounds,” it frees us to simply LISTEN to whatever sound we’re putting through the compressor.  We need to trust that our ears will inform us far better than a number we think will apply.

Before we even get to reaching for the compressor, I always ask my self this: What do I want to accomplish?

If we know ahead of time what exactly we’re trying to do, it makes applying the most musical settings even easier.

ADDITIONAL RESOURCES:

Dynamics Processors by Doctor Pro Audio

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