Easy to conceptualize. Hard to understand. A lot of music listeners don't think about audio compression, but why would they? Many avid fans of music get treated to the end product. Or, the result of hundreds of hours of production work, recording and conceptualizing. The mechanics of such a process often don't cross their mind.
But those who operate at the other side of the equation think otherwise. Compression in music production is rather nuanced as much as it's necessary. It's underutilized and, at the same time, utilized to a suffocating point. Regardless of what most think, compression in audio mixing isn't going anywhere.
How does compression work anyway? That's likely the first question on your mind if you're getting started. Well, why don't we take a closer look at compression and find out.
So, What Is Compression Anyway?
Compression reduces dynamic range of an audio signal's loud and quiet parts. This process essentially boosts quiet signals and de-accentuates louder signals.
Audio compressors lower the dynamic range of the softest and loudest sounds in unprocessed recorded audio. Any piece of music, or sound source in this instance, have different dynamic ranges. Alternatively, dynamic ranges are also referred to as peak-to-average proportions.
When you record sounds, the components of the finished piece will have a unique dynamic range. At some point, this dynamic range needs to be 'cleaned up.' Why? The recording may have playback issues. Electronic systems, such as MP3 players and intercom systems, may reveal uncontrollable sound distortion. If used in an open environment, the unprocessed track might fail to project across the open space.
Audio compression also works for artistic purposes. Vocals need some audio compression to capture specific vocalizations in the final mixed product. Compression also plays a role in controlling a song's dynamic range. This allows recording equipment and other recording related media to better process the song.
Important Keywords to Know About Compression
The art of compression has many nuances. Of course, it also has certain keywords to learn. In this case, there are four you need to know about: ratio, threshold, attack and release.
- Ratio expresses the degree in which an audio compressor reduces the dynamic range of a sound source. It also indicates a certain difference. The difference? The one between the compressor's output level increase and the signal increase that enters the compressor. Ratios get set at a constant value. This means the input to output change ratio always remains the same. Most compressors have ratios up to 8:1. Limiters have ratios higher than that. Professional level compressors typically have fixed selectable or continuous variable ratios.
- Threshold represents the level of an incoming signal where the compressor amplifier switches from a unity gain amplifier into a compressor reducing gain. After the threshold arrives, the compressor reduces gain. Threshold level acts as the compressor's sensitivity level, expressed as a specific level in dB.
- Attack time is essentially the time the compressor takes to begin compressing after the threshold hits. Most attack times range from less than a millisecond (fastest time) to well over 100 milliseconds (slowest time). Attack time settings affect sound quality, particularly high frequency sound or sound brightness.
- Release time is the time a compressor uses to go back to unity gain after an input signal falls below the threshold level. During this process, the compressor releases gain reduction. Most release times range from 20 milliseconds (fastest time) to more than 5 seconds (slowest time).
Gain, which we've used several times by now, is a unit of measurement. Interesting, right? It's used to express the ratio for a system's signal output to a system's signal input. It's most associated with amplifiers. Naturally, it's also used for explaining processes associated with compressors.
Another important key term to know is gain reduction. Gain reduction is a compressor or limiter function that regulates the signal amplification. In other words, it prevents the signal amplification from getting too loud. Gain reduction also keeps the audio signal at a relatively uniform level. Of course, it can also be used to achieve both results.
Make up gain, another term to know, allows compressors to boost compressed signals, since compression usually accents the signal a lot. Output boosts the signal output level coming out of the compressor.
Knee control, much like gain reduction, is another term to know. Knee control changes an audio signal's compression curb shape. A harder knee control setting changes the threshold audio to squash equally along with the audio's compression ratio.
A softer knee controls setting smooths out the audio's compression curb. This allows the threshold level that the compression curb reaches to match the ratio. Harder settings typically work for peak limiting and other 'tricky' audio work. On the flip side, softer settings help flesh out character in audio. Professional level compressors generally allow users to switch between hard and soft knee compression.
Types of Compressors Used in Audio Production
To effectively compress sound, sound engineers use different equipment: compressors, limiters and amplifiers. Each piece of equipment ultimately achieve the same purpose, but in different ways. Let's look at how this gets accomplished.
Day to day' professional compressors: The usual type used in music production. Most recording engineers use models that set attack time and release time settings at a medium threshold. Some producer-engineer teams use high quality compressors. These models feature higher thresholds and lower ratio medium attack/release settings. As a result, it produces a natural sound without extreme compression that maintains most of its dynamic range.
Peak limiters: A type of compressor utilizing a faster attack time, medium-fast release time, and a high ratio and threshold. Peak limiters essential stop or control the fast and sudden peak levels that may overload the next stage of audio work. Broadcast transmitters typically use peak limiters for that purpose. Peak limiters are also utilized for vocal recordings. Sometimes, the producer and sound engineer may want to clean up vocals to better convey a performance.
Leveling amplifiers: A compressor featuring a medium attach time, medium-slow release time, a high ratio and low threshold. A leveling amplifier constantly levels the audio signal while in gain reduction, while smoothly holding the audio signal down. The result typically levels the average loudness of audio at a higher level, allowing lower level sounds to get evened out in the process. Leveling amplifiers, specifically tube leveling amplifiers, typically get used for cleaning up bass, guitar and other instruments.
When starting out, most people generally need an everyday professional level compressor. Most compressors of this level feature enough bells and whistles for the average end user to get started as soon as possible.
Of course, you're not going to get perfect results the first time you try. In fact, using a compressor is considered rather tricky—and the bane of music production at times! But it's entirely possible… covering just how to do that is for another time.
So, compression isn't yet a lost art… it's a necessary one. Compression in audio production helps clean up all the necessary components needed to craft a song or instrumental piece of music. It's a hidden art that makes the music you hear everyday sound great. And, for audiophiles, it's a source of annoyance for those tracks that 'could have been mixed better.'
Still, there's a lot of learn about compression, don't you think? We think so, too. Visit us again to learn more about how to get started using compressors for your own aural works.