Science of Sound: Compression (FaderPro)

Alongside EQ, compression is probably the most common type of processor used by producers and mix engineers during recording and mixing. The full name for this process is dynamic range compression. If you are new to this, it's a helpful term because it tells you that a compressor's job is to narrow or deliberately restrict the dynamic range of the signals it's processing.

You may ask, why would anyone want to do that? If you are working with a skilled vocalist recording a heartfelt and rich performance, ranging from a gentle whisper to an emotive strident tone, why dampen that range?

To understand this, consider how we hear sounds and associate quality with volume levels. We use words like strong, warm, solid, and confident to describe certain sounds within a mix. These adjectives often aptly describe signals that have been compressed.

Our ears are most impressed by signals with a solid average level rather than one that fluctuates. The latter can sound weak, a quality we generally don't want in our recordings. Compressors do more than merely control the average level, depending on their components and settings.

Often, they shape the color and warmth of a sound. While not designed as EQs, harmonic saturators, or distortion units, at certain settings, compressors can add these qualities to the signals they process, enhancing power and sonic footprint.

No wonder most producers reach for compressors for both individual and grouped sounds within a mix. Throughout recorded history, various approaches to compression have been introduced, become popular, and then endured. Many designs, including iconic tube-based compressors like Telephonics LA-2A, still prove popular. They offer a warm, natural response to dynamics control, contouring the shape of sound via two main controls: peak reduction and gain.

Other desirable tube-based designs include the Fairchild 660 and 670, popular as bus compressors. However, the desire for true peak dynamics control remained a passion. The search arguably ended with Bill Putnam's design for the 1176 classic limiting amplifier. Unlike tube-based designs, the 1176, released in 1968, relied on a solid-state transistor-based design, explaining its rapid response time.

Very few compressors have endured by their dynamics range control alone. The 1176 introduced the capacity for tonal aggression, bite harmonics, and extension, and even at extreme settings, saturation of the signal is possible. This explains its enduring popularity across various music genres.

The sense of tonal coloration, or deliberate lack of it, can also set some compressor designs apart. The solid-state VCA-based design of the GBU compressor at the heart of SSL's 4000 series console is renowned for its capacity to glue a mix together while maintaining an almost transparent tonal color. Opto designs like Tube-Tech's CL 1B offer slower responding but musically transparent choices. The amount of gain varies as the light in the compressor's dynamics range reduction circuit grows brighter or dimmer.

Regardless of the compressor type you choose, you'll find core parameters like threshold, ratio, attack, release, knee, and gain to configure settings to your taste. The threshold point sets the volume level above which compression occurs. The ratio determines how much louder a signal can get once it has passed through the threshold. The gain or make-up dial allows you to boost levels to compensate for lost volume during compression. Attack and release times control how quickly signals will be attenuated or recover. The knee control can smooth the behavior of signals around the threshold point.

Read about compression, and you'll find plenty of advice. Some processes may appear superior, but remember that record production history is filled with bold producers making their own choices, like Daft Punk's devotion to the Lysis 3630 Compressor on the Homework and Discovery albums.

Understanding the behavior and tone-shaping capabilities of different compression types is helpful, as compressors can range from transparent to near distorted, hard-limited brick wall effects. New producers often seek advice, but the exciting news is that experimentation is key. Line up multiple compressors, listen to each one, and trust your instincts.

Avoid using compressors simply to boost volume. Many plugin compressors feature automatic make-up gain compensation, tempting users to equate loudness with quality. It is better to switch automatic gain off, set threshold and ratio manually, and then boost levels by your chosen amount to hear the real difference. Take your time, keep listening and comparing, and when you find something that improves the sound of the track, trust your instincts and go with it.