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Immagine del redattoreDino Morabito Studio

The Compressor

Aggiornamento: 15 mag 2020

In this new lesson I will teach you what a compressor is, how many types there are and how it is typically used, according to what processing phase our sound is currently on. The compressor is in most cases an electric/electronic device, unless it is not a digital simulation achieved through the elaboration of very complicated algorithms that process the received digital data. Before going into the modern uses of the compressor it is first necessary to clarify the operating criterion and then to make some premises regarding the intrinsic nature of the machine. Being part of the processors category, it is necessary to first define what dynamics is.


GML Model 8200 The dynamics of a piece in the technical sense is the distance between a minimum value of a sound stream and a maximum value of the same. As an example, we might be recording a human voice whispering something and expressing a rather light sound pressure; we might instead record the moment when this same voice expresses a high sound pressure with a scream. These two moments express very different decibel values ​​and the difference between these two values ​​is represented by the dynamics. The dynamics also has a musical definition that in its most intrinsic meaning is not very far from the technical definition: dynamics is the ability of the musician, in the execution of a part and through the change of the technical gesture in its intensity and its strength, to produce moments of high sound pressure and moments of light sound pressure. In musical notation In fact there are symbols that describe as thoroughly as possible how much force the musician must distribute along the score he is following. In modern commercial music production, dynamic is often sacrificed or managed through dynamics processors such as specific compressors or limiters in order to make it easier to listen to on systems of the most diverse nature. Yes, in fact, modern music makes a massive use of the compressor and this comes from the fact that what is recorded is what is mixed and what then burns is intended to be heard in a very compact piece in which the natural dynamic expressions of each instrument have a very small space. Often the strategic choice on how to let a song breathe or on how to make it evolve for those who then perceive it is left to the arrangement and the timbric nature of the instruments that are playing at that moment.


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To give an example, the moment in which we pass from the refrain to the break in which often from the massive presence of all the instruments we pass to an "emptying" as we say in jargon. Another example is that of the voice that can take different timbres, different suggestions and different perceptions depending on whether it is screaming, modulating, or whispering. Knowing therefore that in the production of a piece of modern music we see a massive use of the compressor, we can clarify that its use can be found in the recording phase, in the mixing phase and finally in the phase of mastering or finalization. Now we are ready to go into its operation, taking into consideration the individual devices present in the machine, their operation and what to do in order to manipulate the dynamics of the sound subjected to treatment. Naturally I won’t explain its operation in electronic and electrical terms, for this I could make use of the advice of an expert, but it is not the right place. The devices that we can usually find on a dynamics processor are in order:

The Input value I’s a device that gives us the possibility to decide how much sound to feed our compressor.

The Threshold The threshold beyond which we decide that the sound must be subjected to the treatment.

The Ratio You can read this as “how much you’re compriming” and is usually an expression of a relationship. For example, if our ratio is programmed according to a value of 1:3 it means that every unit of sound that the dynamics processor modifies (those over the threshold) is reduced to one third.

Attack time It’s expressed in milliseconds and it is the time that elapses from the signal exceeding the threshold to the compressor entering into action. This device in effect depending on how much value we give in ms can even change the timbre and the structure of the sound processed, for example if we are compressing the sound of a battery drum, the wider the attack value the more we will avoid compressing the initial part of the sound of the, where the higher frequencies reside (the strike of the pedal's hammer on the skin of the drum).This way we will obtain a sound with a more pronounced expression of high frequencies. In fact it is as if we used the compressor as if it were an equalizer, but with very different specificities and potentialities.


Release time It is also expressed in milliseconds and is the time that elapses between when the compressor starts to actually compress to when it stops doing so. Naturally, this value also determines the modification of part of the tone of the sound we are processing.

The Knee The Knee is a device that softens the activation of the compressor in the actual moment of its operation, that is, when the attack value is triggered. Imagine the switch of a light bulb that turns on and off a light bulb; here the Knee device instead takes the role of a sort of dimmer that allows to precisely determine how much light to let through. Output value Finally, the output device allows us to measure the amount of sound flow we want out of our processor. This is a rather general overview of the devices that we can find inside a processor, obviously which you can find can change depending on the model of the compressor, the brand and date of manufacture.


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From a very general and academic overview like ours, we can only deduce the logical principles of operation of a dynamics processor, not what it offers us in terms of processing opportunities in daily use.Use, experience and experimentation can sometimes reveal opportunities that otherwise we could never get from our machines with a purely - let us say - scholastic use. For example, the things we have to take into account, especially in the physical processors of dynamics are the components, the design of the electrical circuit and the quality of the elements that assemble them and make up the circuit. This because it is known that beyond mathematical principles, the circuit adds a quantity of electric charges that enrich the sound and make every model or brand of dynamics processor generate a compression characterized by a particular tonal nuance. In a nutshell I mean to say that every compressor has its own sound, if you have to buy one inform yourself, listen to the way it processes the sound, ask questions to those who have had experience on certain machines and collect as much information as possible. In truth this does not happen only with the dynamics processors, but also with all those physical machines that manage the sound flow, from microphones to mixers. Every electrical circuit, every valve, every component can attribute a particular tone to the sound we are dealing with. If we’re talking about digital compressors on the other hand, the situation changes completely. We started in the mid-90s to have the first digital dynamics processors mounted on the sequencers progenitors of the current ones. They were using a simple mathematical operation in the form of an algorithm that changed the sound in a very different way from a physical compressor. Nowadays, programming has made great strides and we can work with plug-ins that, in addition to algorithms changing the sound to compress it according to our wishes, can also simulate all of the harmonics that give that peculiar timbre to the sound or, at least they come close to imitating certain types of timbres generated by physical machines. Naturally, the plugins that simulate the dynamics processors have a more restricted application compared to the physical machines as what we can develop within a sequencer is more restricted. Basically, getting good recording quality is difficult using plugins with improbable circuitry. So for microphone recordings or recordings in general we rely on physical machines, knowing beforehand what kind of machine reflects our tastes and which are the machines that can fit within our budget. If our working environment is a Home Recording it is particularly important to opt for machines with a high degree of versatility.




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I would now like to draw some principles and general rules for the use of these machines. First of all, I distinguish two moments that are absolutely different from each other. The first is when I record a sound, the second is when I have to insert this sound into a mix. When I record a sound, such as a voice, I rely mainly on the quality of the circuitry of the machine, the quality of its valves that help to give me a richer and warm tone and having the need to restrict the dynamic range of what is being recorded, my most used devices are the input and output values ​​with the ratio, release and attack being altered only slightly.


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Know that the values ​​of Ratio, Release and Attack if used conspicuously and heavily can help to transform your sound completely, both in the timbric content and in the dynamic behavior within the mix. So if you do not want to do sound design immediately you should record the sound in its purest form. During the mix this changes. In this second moment the space for creativity is much wider, the attack time, if wide, can exacerbate and harden the sound, the release time can round the sound of a bass, and a precise combination of the two with a well-calibrated ratio can make us get grooves with the right nastiness. If the sound has been taken according to the right procedures, with the right microphones and with the right preamplifiers inserting it into a mix and filtering it with good plugins that simulate dynamic processors is a breeze. in fact, our creative sphere acquires even more freedom. Versione Italiana

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