The use of compression at professional audio mixing

Compression basics

Dynamic processing devices represented with a great variety of compressors, limiters and other appliances are now an essential element in professional online music mixing. They allow an engineer to control dynamics of musical instruments in a flexible way by reducing the difference between the loudest and quietest parts. The use of compression allowed mixing edm music engineers not only to enhance the loudness of single sounds and songs on the whole, but also to get sounding of live performances and records much more “stuck together”. Another most important aspect is also the possibility to give a sound the coloration with extra harmonics added by both hardware and software studio devices. In the 

professional engineer’s hands, compression is an instrument which turns live but rough dynamics of live performance into an organic comfort track to listen to. Compression puts life into initially dull sounding as well. As opposed to it, the unskillful use of dynamic processors brings about overcompressing and pressing life out of a music track. This article will be helpful for those who are new at music mixing mastering with compression and nuances of dynamic processing. In this article, I’m going to consider basics of one of the most important aspects of audio mixing  practice, parameters of compression and their significance as well as a number of defining characteristics of devices and specific cases of their use. So that in your further engineer practice you will be able to consciously and creatively use various kinds of compression by turning ordinary sounding of a raw record into excellent audio rich in color and character where each sound softly gets blended up in the general set of arrangement and clearly occupies its own niche. 

To Compress or not

As a matter of fact, any device of dynamic processing in mixing and mastering (whether it’s a compressor or a limiter) is a sort of enhancer which operates by the method of reducing the difference between the quietest and loudest parts of an audio signal. The reduction of this difference gives a sound much smoother, more polished sounding due to the control over peaks and a lot higher values of perceived loudness what allows an affordable rap music mixing and mastering engineer to get an instrument involved in a final track in a more comfortable way during music mixing. As an addition (I was speaking about it earlier) all vintage compressors and their contemporary digital emulations are used as another technique for sound coloration by means of added by their chains harmonics and saturation that 

turn mixing literally into reanimation of plain and uninteresting sounds. The use of compression in professional online mixing and mastering services in studio is also a fine way to literally massage a track by giving it more natural sounding. What is more important, this sounding is far more comfort to listen to without any deafening splashes and scarcely intelligible loudness dropouts. You should above all know where to draw a line and clearly realize the final cause of your actions! Mixing with an awkward and uncontrolled use of compression can press all life out of audio and turn music into a hardly intelligible track full of distortions. To avoid it, let’s get to know basics of compression and main settings the fine use of which gives an engineer a total control over a sound. A little of theory, permanent practice, the analysis of the work done – and your music studio will turn into a laboratory for creation of new masterpieces. 

Main Control Devices

Whether an engineer prefers using plug-ins or hardware processors, there are parameters which are common for all devices. They let engineers set the character of a compressed sound in a flexible way during professional online mixing services. Let’s consider them in details. In fact, each model doesn’t need to have all these settings, and part of them can be fixed or have autosetting. Yet you must realize the essence of their impact on a sound to use compression consciously during online mixing and mastering service.

Threshold

This parameter defines audio loudness during which the device starts processing a signal. For this purpose, everything what is below the given volume remains unaffected, and peaks which go beyond the preset threshold level are being compressed. So, if the online audio mixing  engineer preset the level of threshold in 10 dB, the compressor will be running idle until the splash of an audio signal overruns this value. In the meantime excessive loudness will be reduced according to the other device settings.

Knee

This parameter defines the behavior of a device during the transition from the quiescent state to audio compression. Most of studios are equipped with compressors which offer either soft knee function during which the signal starts compressing smoothly while approaching the preset threshold or hard knee when processing is switched on as soon as the level preset by an engineer has already been achieved. There are also devices with switching of temporary fixed values and even with manual setting of knee parameter what has also become commonly used in professional music mixing services with compression. While choosing between soft and hard knee, the  mixing  engineer defines whether compression will be evident or soft and unnoticeable. 

Attack time

By setting attack the online audio mixing services engineer defines the time during which a compressor achieves the maximum value of audio compression. Depending on creative tasks of a  studio, there are two kinds of compression used – with aggressive settings (attack in the range of 80–200 microseconds) and fine compression in the range of 10–100 milliseconds. The lesser length of attack allows a compressor to respond to loudness changes faster, but in some cases it causes audible distortions. And if an evident sound overload wasn’t devised as a specific affordable mixing and mastering services technique, the attack should be enhanced to make the work of a compressor more unnoticeable. The source audio material also influences on the selection of a parameter, for instance, drums mixing requires a much faster attack so that the device will manage to respond to short explosive transients in time. It’s all less obvious for vocals and depends on both sources delivered to the studio and the audio engineer’s innovative take.

Release time

It’s here just the opposite. This is the time during which audio changes the complete compression state to the source uncompressed one. The value range also varies widely depending on the tasks set for the mixing mastering services studio and on an instrument which is being processed. To sum up, much shorter release time makes compression more unnoticeable and allows audio mixing engineers to achieve a larger reduction level without any audible distortions during mixing  while longer release time gives larger sound density. When the value is excessive, pumping effect can appear – nevertheless, many studios use it as another technique to add the character and some aroma of vintage records to the sound.

Compression Ratio

This is probably the most wrongly treated setting parameter. In fact, it’s all quite simple – when the audio engineer sets ratio value, he defines how much the audio which overruns the threshold will be compressed, in other words, literally how many times quieter these peaks will be after processing. So ratio 1:1 means that the signal won’t experience any changes. If the ratio makes up 2:1, the peaks at the output will be twice quieter. For example, the signal that has overrun the preset threshold by 8 dB will be attenuated by 4 dB. In practice of professional rap hiphop mixing and mastering, ratio values of 2:1–3:1 are considered to be moderate and used for the most possible unnoticeable intervention in sound dynamics. Value 5:1 is already the compression of medium hardness (it’s frequently used for drum mixing; drums’ character is explosive and dynamic by nature). 8:1 is a fairly powerful compression with an evidently audible effect. The values from 20:1 and higher up to ∞:1 (infinity to one) mean that the compressor is already working as a limiter by limiting peaks hard without letting anything higher than the preset threshold to come past. It’s often used in professional music mixing  for adding evidently distorted smashed sounding.

Output Gain

Although the role of compression in enhancement of perceived loudness is well-known, in fact, these manipulations break the natural structure of the recorded signal and make it sound a lot quieter… But here “Output Gain” and ‘Make-up Gain” are coming into play. Through this parameter, the mixing mastering engineer restores the loudness lost due to processing. As a matter of convenience many devices have “Gain Reduction” meters that allow engineers to track the work of a compressor during mixing and to use correct output gain values.

Main Kinds of Compressors

It’s worth keeping in mind that compression in mixing is more than just a “mathematical” reduction of audio dynamics. Depending on the producer and the kind, devices can have much faster or slower attack and release according to declared values. They can also add the coloration to the sound with an emphasis on various frequency ranges. That is why every studio is equipped with a great variety of gear to solve specific creative tasks. Let’s consider the best-known kinds of compressors and their distinguishing features made them widely used at professional mixing mastering music with compression.

Tube compressor

These devices were practically at the dawn of the science of audio mixing. Thanks to circuit technology tube compressors have slower attack and release as well as evidently expressed audio saturation. In the whole these nuances give the sound clearly expressed vintage character which has been popular up to now.

Optical compressor

It is based on “light emitter-optical cell” pair. It causes a slow respond of the device to level changes and characteristic softness of the work. Thanks to it engineers use them to process vocals, bass and an electric guitar. They also give an interesting effect during kick drum mixing with compression.

FET compressor

The name of this kind is deciphered as Field Effect Transistor. Perhaps, their best-known representative is a classical model 1176 and its multiple clones widely used in music mixing mastering services due to the speed of the response and distinctive coloration.

VCA compressor

Thanks to a lower price and lack of evident sound coloration, which both optic and tube devices have, Voltage Controlled Amplifier compressors are also popular with many audiostudios. 

In the end, there are some recommendations from experienced mixing audio services engineers. The rules aren’t strict but if you use them, it will be a good scene starter in your development as an engineer. The only rule is keep experimenting!

– During recording and then mixing and mastering rap hip hop it’s more preferable to reduce dynamics stepwise, gradually at each stage than use excessive compression applied at once.

– It’s very important to choose a device for an exact task. For this reason, another device isn’t a whim but necessity for productive work of a mixing services  studio.

– Start with moderate compression (ratio 2:1–5:1; medium attack and release time). Achieve about 5 dB of gain reduction – now you can play with attack and release settings while watching the sound character changing. This practice is extremely helpful for a would-be audioengineer.

– Try dramatic compression on drums and an electric guitar. Some aggressive flattening often happens to literally liven up dull sounding of a raw record!

– To add larger adhesion, compression of the whole track is practically always used during music mixing with compression. However, splashes of bass and low end elements of some instruments cause “pumping effect”. There is a multiband compressor to help engineers to avoid it. This compressor allows them to pick settings particularly for every frequency range.

– Crank up the ratio is a trick of which a lot of engineers are fond, use it and achieve 6–10 dB of gain reduction. Now the manipulations with attack and release time can be heard far better, and they let engineers select their exact values.

– And the key point! Your hearing is a chief referee! If a professional engineer has put the cap on rules, but you like the sounding of the song, it means he has done everything correctly.