Learning to hear compression

When you listen to an album, there is what we call a sonic shape to the mix. The sonic shape is characterized by an overall tone, energy, and focus of the sound. For many, they can hear the differences in sonic shape, but are unable to put a finger on what they are truly hearing.

Understandably, it is hard to characterize an entire mix because by nature it is very dynamic, complex, and involved many layers of processing to obtain the album you are now listening to.

So let's start with compression. Compression is a restriction on the loudness of sound. Compression is everywhere. In microphones, the ribbons or coil diaphragm of the mic can only capture so much audio energy before they reach start reaching their natural limits. However, as sounds become louder, microphones actually exhibit small levels of compression in their physical designs. Thus as sound pressure becomes more intense, the dynamics and clarity of the microphone will start to be lost.

If you stop and think about this for a moment, the same thing happens to our ears. As sounds become louder, the dynamics and clarity between notes becomes harder to hear. There is a sweet range somewhere around 83 and 88 dBs where we can sense a fullness and dynamic range in audio. As you progress past 90 dBs, sound increasingly becomes harsher and the subtle dynamics are hard to pick up. Why is this? Your ear is experiencing a certain level of overload and compression. Continuing to listen to sustained audio levels at high dBs causes hearing damage due to the destruction of the sensitive hairs and nerves in the cochlea of the ear, just as the sensitive ribbon in many dynamic microphones will tear if exposed to excessively harsh sound pressure.

Compression also naturally occurs in speakers. As the coils of the speakers become energized, the dynamics and available headroom change. While gradual at first, a speaker will start to distort and the clarity and dynamics of the sound it is producing will breakdown as it is further energized and pushed towards its limits. 

Compression is a natural phenomenon that you must control or it will occur outside your control.

Compression in audio is all around us and we must control it. So let's discuss what the results of applying good and bad compression (harsh limiting, poor timing) sound like.

Good compression sounds like:

• Clarity at all times

• Instruments' tones and sounds kept under control

• Dynamic range with a punch and smoothness

Bad compression sounds like:

• Harshness or loss of clarity in powerfully loud sections 

• Overly constrained sound without dynamics

• Sounds which feel snapped or unnaturally cut in terms of the clarity, especially on the first note

• Loosing vibrance as low-end frequencies increase on a channel (compression applied to the entire audio range)

A complete lack of properly applied compression sounds like:

• Instruments fighting for center stage in a mix

• Loudness and dynamic constantly at war in the mix without resolve

• A mix that sounds hollow, because increasing volume creates a loudness war

• Pops, feedback, and harsh sounds occur without control 

• A mix you know could sound better, despite EQs being dialed in and a talented band.

Why this is important

I once stood in one the world's most advanced music chambers in the world at Liberty University in VA. What makes the room breathtakingly beautiful is the way in which it can function as a rock hall or as extremely well engineered recital hall. This is due to the Constellation system by Meyers Sound and a tremendous audio reinforcement installation. More on that in another article...  I will never forget what the head engineer told me about the space. I had been talking with him about employment opportunities in mixing and my passion for tackling the hardest most complex mixing situations. His response was, "In this space, there is no forgiveness. Unlike larger venues such as (Liberty's) Vines Center, this room will reveal your mix without forgiveness. There is no hiding from a bad mix in this space." His perspective was actually rather interesting. He believed it was harder to obtain a quality mix in an extremely well tuned space than in a large venue where the reverbs and delays in the room conceal errors in the mix.

In spaces and venues where the sounds bounce and clarity is naturally lost, there is an element of hiding that takes place for most engineers. The true clarity and precision of their mix is somewhat unknown to the audience due to the obstacles of the room. One of the ironies of a well tuned room is that it often makes a bad mix even more obvious. By dialing in the system dynamics, your actual mix will shine through.

How does this relate to compression? Compression is ultimately about controlling the energy of sound in your mix. EQ can control the shape and tone of each instrument, but compression helps keep everyone in check. In another article, I will discuss how the use of compression properly actually allows greater dynamics and more punch in your kicks, bass, and energetic sections of tracks.

If you ever listen to an album and the clarity is lost in a loud section or the high-hats seem to overwhelm and loose their clarity and flavor, or the bass, synth, and kick all join up to overwhelm and push out the high-ends and clarity of a mix in a swamp of moodiness... this is all due to a lack of proper compression on channels. The fault is typically the engineer's, not the band.

Let's discuss vocals for a second. One of the best ways to approach vocals for a studio sounding mix is to apply two layers of compression. The first compression should be a low ratio compression, which slowly pulls down the energy level as you cross your threshold. The second layer of compression should be more aggressive, helping to establish a maximum energy allowed for the vocals. Using a two step approach to compression maintains dynamics in the vocals while keeping them under control. By adding a slight EQ after the second layer of compression, you can further help shape the final tone of the voice to bring clarity and air to your vocals in a way not possible when you only apply EQ only before compression. This is a trick applied by the more advanced audio engineers with powerful digital mixing boards which can handle multiple processors.

There are many examples of poor compression out there. Begin actively listening for distortions, especially in the higher ranges and you will quickly learn what a lack of compression can do.

Pro tip- You want to know how good your live mix actually is? With slight adjustments to EQ, your live mix should sound just as good during playback on any device. If your mix is out of control, then when you play it back, you will notice a wild difference. Remember that people now compare our mix to the very best in audio. Your standards for mixing as a result must be set extremely high to deliver a mix that sounds good.