Would you agree compression is one of the essential practices during mixing? You use it on every tier of a mix, often on every track regarding a given session. And would you also agree that sometimes working with compressors can get tedious, repetitive, or become a mindless routine? Today, we will look at the collection of tips to help you release the pressure of guesswork and compress more mindfully and effectively. Along the way, the main compression parameters and the most significant types of compressors will get explained. First of all, making sense of the underlying components of compression.
Threshold & Ratio
A threshold is a level that an audio signal needs to hit for the compressor to activate and start to do something. How it works can differ as well, depending on the design. Sometimes you can set it manually, sometimes it is predetermined by the circuit, and you drive the audio signal towards the threshold with the input control. (That is how FET compressors work.) A ratio means how much compression gets applied to the signal. It is the relation of the input and output signal in dB. Regarding ratio, you will see settings such as 2:1, 4:1, 8:1, 20:1, and similar. It means for how many input dB one dB gets outputted. Therefore, with a 2:1 ratio, for every 2 dB coming in, 1 dB of the output signal comes out, and so forth.
Attack & Release times
An attack time of a compressor means how quickly or slowly it starts to work concerning the transient of the audio source. The quicker an attack is set, the sooner it compresses the transient of a note.
A release time of a compressor means how quickly the compressor recovers after the signal falls below the threshold value. The slower the release time is set on the compressor, the more challenging job it has catching the next incoming transient.
Differences between compression and limitng
Although it can confuse users these days, many classic compressor hardware units are marked as limiters and amplifiers. The explanation is that they formerly served mainly for broadcasting purposes (or as a protective device during vinyl cutting), where limiting was their first objective. In their nature, they are both amplifiers and attenuators. Circuit-wise, they often start with amplifying the signal, which then hits a fixed threshold, and, based on the setting, gets attenuated. Then the make-up gain is applied to compensate for the volume loss.
Contrary to limiters, which mostly have a short attack and high-ratio downward compression in their core, the attack, release, and the ratio of compressors can vary more.
When working with a compressor plugin, setting the time parameter yourself means you can fine-tune compression attack or release (or both) to the desired effect. And it can do wonders when manipulated wisely in a mixing environment.
Types of compressors
Optical compressors convert audio to light and depend upon the input amplifier (which changes the brightness of the electroluminescent panel picked up by a photocell) to predetermine their attack time as well as the release time as a consequence, too. Generally, they are slower, the amount of compression is set by controlling the amplifier, and have lesser sound coloration.
VCA (Voltage Controlled Amplifier) compressors convert input audio to a voltage which then controls the attenuation of the output signal. Therefore there is much more to manipulate manually, such as the attack time, release, threshold, and ratio. They are fast and versatile, and they introduce almost no distortion. Many stock DAW plugins build on the VCA design.
FET (Field Effect Transistor) compressors are fast. The gain reduction is achieved via a transistor circuit, and there is almost no limit to how swift its reaction can be. The detection circuit compares the amplified input signal to the fixed threshold – therefore the input is the only parameter that determines when does this compressor work. And based on the ratio settings, the gain reduction part of the circuit is performed. There is output or make-up gain control to compensate for the volume loss. FET compressors are handy for making the audio punchy and more driven.
Tube (Variable-MU, Delta-MU) compressors are not dissimilar to optical compressors concerning their use and reactivity, although they are often even slower. The key difference here is the compression itself is done via the tube, and as a result, these compressors often introduce saturation to the signal too. The more the input gets driven through the tube, the more the detection circuit sends a negative charge to the tube grid, changing its bias and making it harder for the audio signal to pass through, which means compressing it more.
Tube compressors are great mastering tools. They can either subtly or heavily color your audio and add a character to it. They produce more distortion and are less transparent than an optical compressor. But the consequence is that there are additional more even-order harmonics created, making the audio often more exciting sounding. They can be an inspiring addition to your color palette. No matter if you focus on mixing old-school vintage rockabilly or top-tier modern metal.