COMPRESSOR IN A MUSIC STUDIO?

This article will discuss compressors and their use. It is perhaps one of the most debated and mysterious pieces of equipment in studio technology.

Undoubtedly, this topic is associated with the most urban legends. Perhaps this informative article will clear the air. We will delve into their operating principles and uses, as well as the equipment that has been instrumental in the history of music and has influenced the development of popular music.

If I were to answer the question posed in the title in one sentence, I would be in great trouble, because the answer is not that simple. One of the key issues in music is dynamics, and these devices certainly manipulate dynamics. If we ask a musician what dynamics are, they usually cannot answer precisely, but they naturally feel or sense what it is all about. This is a subject that people tend to feel rather than know. However, it is beneficial for those involved in composition and orchestration to be familiar with the basic concepts of dynamics. In everyday language, we tend to call something dynamic if it is loud. The opposite is almost true: if something is loud, its dynamic range is usually narrowed, meaning it lacks dynamics! Let’s establish from the outset that dynamics refer to the difference between the loudest and quietest parts. The dynamic range is the zone between the quietest and loudest peaks. Contrary to common parlance, something can be called dynamic if the full range between the loudest and quietest peaks is heard in its raw form, meaning its dynamics have not been subsequently interfered with. I emphasize once again that what is loud is not necessarily dynamic.

In this topic, the concept of transient is very important. A transient refers to the beginning of sounds, or the sound’s attack. The human ear and overall human perception treat this quality with special importance. During hearing, we perceive sound attacks, or transients, most sensitively. For example, whether we perceive a snare drum as punchy or not is decided based on its transients. Based on transients, we decide, among other things, whether a sound is clean or dirty, washed out, characterful or not, and so on. Generally, when we make any judgment about sound, we usually do so based on transients. In other words, a transient is the first 10-30 milliseconds of a sound, to which the human ear is very sensitive, and therefore plays a crucial role when we talk about dynamics. It is difficult to answer the question posed in the title because when comparing raw material with a compressed version, I always feel that something is lost during compressor use. Why then do we use compressors – the legitimate question arises. Moreover, why were such devices invented at all? This is where the contradiction and mystique of this topic stem from. Is it better not to use them? Why are they even necessary? The situation is much more complex than that! If we listen to live music in a concert hall with excellent acoustics, without amplification or any intervention, then ideally, every frequency range is distributed equally, and we can hear the live music with balanced dynamics. When making recordings, unfortunately, it is not so easy. We must be aware that all recording is an illusion. We generally want to create the illusion of an orchestra performing ideally in excellent acoustic conditions. The best advice for the young generation of producers is to attend classical music concerts in concert halls with good acoustics multiple times to experience what perfect sound reproduction is like; I recommend listening to Mozart’s symphonies. Personally, I consider Mozart the best sound engineer of all time! Before mixing, one must experience good sound to be aware of the illusion one wishes to create. Perhaps the best approach is that the compressor is one of the tools for creating this illusion. Ideally, we are talking about instruments with equally dynamic sound. In reality and in recordings, instruments do not sound with balanced dynamics – we use compressors to correct this.

It is time to learn about the operating principle of compressors. For simplicity, let’s consider a machine with a general operating principle. Most compressors feature potentiometers labeled attack, release, threshold, ratio, and make-up gain. Let’s start by defining compressors as devices designed to narrow the dynamic range. A good compressor is one that narrows the dynamic range while balancing the dynamics of the compressed instrument. For example, sounds played on different strings of a bass guitar will sound equally loud. Threshold means ‘küszöb’ in Hungarian. This potentiometer sets the value at which the device begins to operate. This means that if there is a loud part in the given track that exceeds the threshold, the device will engage. If the volume is below the threshold, the device leaves the audio material unchanged. Ratio means proportion. With the ratio, we can set the compression ratio. For example, if the ratio is 1:3, then if the audio material goes 3 dB above the threshold, the device narrows the dynamics by 2 dB; if we exceed the threshold by 6 dB, then by 4 dB; if we exceed the threshold by 9 dB, the dynamic range is narrowed by 6 dB. From another perspective, if we have exceeded the set threshold value, then at a 1:3 ratio, for every 3 decibels at the input, the response at the output is 1 decibel; if the ratio is 1:4, then for every 4 dB at the input, the response at the output is 1 decibel, and so on. The ratio value determines the degree of compression. Above a value of 1:10, we are no longer talking about a compressor but a limiter. The attack and release potentiometers are the time parameters of compressors. Attack determines how quickly or slowly the device reacts if the material exceeds the threshold, while release determines when the compression ceases if the volume falls below the threshold. It is worth learning to consciously use these two time-related parameters. Because with conscious use, we can manipulate the beginning of sounds, the transients, and their decay. If we set the attack time parameter too short, we might aggressively interfere with the sound’s transients, thereby degrading its quality. A too-short release time value, on the other hand, causes undesirable, unmusical pumping.

Of course, using long attack and release values is not the solution in every mixing situation. Experiment with different parameter settings on as many instruments as possible, because the first step to correctly using compressors is learning to hear their effect on the material, even with minimal compressor use. We are talking about very subtle sonic differences that simply need to be learned to be heard. A lot of experience must be gathered to develop the skill to register even the tiniest differences. If we consider that compressors interfere with the rhythm of music, the mystique surrounding them intensifies even further. All devices work with time constants, so their use can alter the fundamental tempo of the audio material. The goal should be for this intervention to enhance the pulse of the music. With clumsy time parameter settings, the pulse of the music can very easily be smoothed out, which should be avoided in all situations. If we learn to use these dynamic processors, we can enhance and emphasize the tempo of the material; otherwise, with unprofessional use, we only worsen the situation. The most useful advice is that until we have fully mastered their use, we should apply these devices cautiously and minimally! A good starting point is to begin with the processor’s preset parameters and then try to find the appropriate setting for the given situation from these settings. The make-up gain or output gain potentiometer is the last potentiometer we want to discuss in detail. Most analog and digital devices have a meter scale on which we can read the level of the compressed audio material. It is very important that the volume on the input and output sides matches, because only then can we make decisions. It is a fundamental human trait that we always perceive something louder as punchier, more distinct, or bigger. If, when using a compressor, the output volume is louder than the input, we deceive ourselves, because we will have the illusion that the processing made the track so punchy. And conversely, if the input volume is greater than the output, we might get the impression that the sound becomes smaller with the use of the processor. In all cases, the volume of both sides must match, because only then can we make correct decisions and learn to hear their operation. If we have several years of experience using compressors, we can conclude that compressors can influence not only the dynamic range but also the timbre itself. If we use a slow, sluggish compressor, the track will also be slow and sluggish, and its transients will be less emphasized, thereby resulting in a less bright sound. American literature refers to this as a dark sound. If we use a device with a fast response time, the transients of the sounds are emphasized. The sound then shifts towards the highs, or becomes bright. This topic, how different devices color the sound, is so complex that I recommend it only to advanced readers. Of course, here too, I can only advise a lot of experimentation and experience.

The previously mentioned Levelling type compressors mostly operate on a photo-optical principle. From the sixties and seventies to the present day, numerous such devices have been used in recordings. The third type is FET (Field Effect Transistor) compressors. One of the first such devices is attributed to Bill Putman. In the mid-sixties, he built the now legendary Urei 1176 model. This type, unlike the previous two groups, is a very fast-reacting and punchy machine. It had an unimaginably great impact on the development of popular music and sound recording culture. Punchy and aggressive drum and bass guitar sounds are virtually inconceivable without this device. For example, the hard rock/metal music of the seventies would not exist without the Urei 1176 Limiting Amplifier model. This type has seen numerous variants. Urei manufactured it continuously for over 10 years. Its sound is characterized by being built from transistors originally developed to simulate tube sound. In the sixties, the EMI-Chandler company in Britain produced similar equipment. It is perhaps impossible to list all the companies that produce analog and digital copies. The fourth type of compressor appeared in the mid-seventies and also had a great impact on the music industry. This type owes its existence to the rapid development of integrated circuits. This group is VCA compressors. Microchips perform volume control. The DBX company was the first to introduce a machine operating on this principle. The 160 model has now become a classic. These are also processors with fast response times. They can be successfully used on almost all types of audio material, from drums to mastering. DBX quickly created a few variants, named 161, 162, and 165. After a short time, they put their inventions up for sale. The Oxford-based SSL company built these circuits into its large mixing consoles. The 4000 series master bus compressor became so widespread that the pop and rock sound of the 80s would be unimaginable without it. The Valley People Dynamite device, which also works on this principle, became popular for mixing alternative rock. Most commercially available compressors today are of the VCA type. This type is also the most widespread in sound reinforcement. After the evolution of analog devices, we are now at a point where we use almost all types during sound recording. Digital signal processing processors can be categorized into a fifth group. This includes plugins, which most modern producers know and use. It would be too early to describe the history of plugin compressors.

At the beginning of the article, I tried to answer what these over-mystified machines are and why we use them at all. We can narrow the dynamic range with several types of equipment, but what truly makes us masters is discovering which device can create the illusion of perfect sound in each mixing situation. I cannot emphasize enough that we will need a lot of experience if we want to reach the highest level of using devices that manipulate dynamics. One of the most important considerations when using them is to define for ourselves what artistic goal we want to achieve during mixing. Let’s develop our own artistic credo, the illusion we want to create. Let’s not forget that these processors are merely tools for creating illusion.

Author: Szabolcs Puha

Source: http://soundhead.hu