It’s important to understand how compressors and limiters work to control the dynamic range of you audio. Use these to for a polished final project.
You just sat down, you got your jumbo popcorn in one hand, your overpriced candy in the other. The lights slowly fade down… it’s preview time! The announcer reads, in a sweet, sultry voice, “coming this summer…” your seat rumbles and you can feel his voice in your chest. It’s very likely, if you met the man speaking on the street, his voice wouldn’t invoke the same magic. This is a classic situation where the knowledge of compressors not only has changed the viewer’s experience, but also has made a man with a voice a career. Many voice over artists keep their compressor settings and even the brand of compressor they use a trade secret. Even going as far as to put that compressor on their phone, so they always have that big voice. It’s important to understand how a compressor and limiter work. Being able to get the most out of the audio you are recording will make your final product shine and rise above the rest. Compression reduces a signal’s dynamic range and results in a more even signal. The classic example of this would be a scene in that starts as a conversation between two people, and ends in a yelling argument. At the beginning, steady calm conversation, by the end loud yelling. This is a perfect time to apply some compression that will bring down the more aggressive sections, while boosting the softer passages. Dynamic range is the ratio between the softest to the loudest sound. The dynamic range is measured in decibels. Compressors, expanders, and noise gates are processing tools that affect the dynamic range of a sound source. The goal is to get a consistent sound when recording without sucking the life out of them. Compression is one of the most used audio processes out there. It can make even the smallest sound big! Simply put, a compressor controls the dynamic range of whatever sound you’re putting through it. It can be used to reduce the fluctuation in volume from a sound that has a huge dynamic range, or to simply accentuate the warmth of a voice over. In the field, you’ll encounter the need for a compressor often when dealing with on-camera dialogue. Some people and things naturally have a large dynamic range. As intensity increases, so does the dynamics of one’s voice. A compressor will control the dynamic range so that you don’t get too loud, or too quiet. The tighter you compress, the less the dynamic range you’ll have. A good visual is a soda can being crushed. The can as it was made is one size, but when you crush it, or compress it, it is now not as tall. You now have just as much can as before in a smaller tighter package. A compressor does this too, but to an audio signal. Let's jump into the individual controls of a compressor. The threshold is where the compressor will begin to reduce gain. If the level of the sound source is above the threshold the compressor will start to attenuate the signal. An example would be if the threshold is at -12db then any input level above -12db would be reduced. If the input is below the set threshold point, then it would not be affected by the compressor. When the input level goes above the threshold you set, the compressor reduces the gain by a factor you specify known as the ratio. The ratio is the strength of the compressor. It’s how much attenuation is applied to your input when it goes above the threshold you set. The ratio is made up of two numbers. The first number is the input and the second is the output, let’s take a ration of 2:1 as an example. A 2:1 ratio means that the compressor will allow 1db of output for every 2db of input. At this ratio, an input that goes 8db over the threshold would be reduced by 4db on output. At 5:1 an input that goes 10db over would be reduced by 8db on output, because for every 5db over the threshold, it’s only allowing 1db of output. The attack is the amount of time it takes the compressor to get to full cutback after the threshold is reached. Since the attack is a time controller, it’s adjusting the amount of time it takes the compressor to kick in. This isn’t a delay of the threshold, but rather how long it takes to get to full power. The attack is measured in milliseconds. The release is the opposite of attack. It’s the amount of time it takes the compressor to stop after the given input has fallen below the set threshold. It’s the amount of time you want the compressor to take to stop working. Because you are compressing the signal being processed, the peak level is now lower than the original. The makeup gain, or output gain is where the final level is boosted because the product has been compressed. It allows you to have a healthy signal again, now controlled by a compressor. Now that you know what each control does and when to use it, let’s complicate it a bit-by talking about a multiband compressors and other dynamic controls. A multiband compressor divides frequency band into groups. It does this so that each section has its own compressor. That means you can have different controls for each frequency band. Need punchy low frequencies? You can set the compression up differently than the hi frequencies. With a multiband compressor,you can design the compression for each different element in your mix and compress the recording more transparently than with just a single-band compressor. You’ll find either 3 or 4 different bands in a multiband compressor. Be mindful of the crossover frequencies as they are the range of frequencies of overlap, getting them right isn't simple, but if done well, it will make a great impact. A solo function is typical to find on a multiband compressors. It will allow you to focus on one band at a time — this function will be a key when trying to get the crossover frequencies just right and when setting release and attack times. The best part about a multiband compressor plugins, just like most plug ins, is that they come with presets. These presets are a good starting place, when setting up your compressor. Start at the preset and then adjust them from there to fit the current need. It’s key to make sure that what you are doing is making the sound better.Listen closely to hear what changes are occurring. To test this, try bypassing the plugin so you can a/b the compression settings to hear what it's doing to the track. A limiter does something similar to a compressor, in fact, most compressors can effectively be limiters. A limiter is a process that is set up to limit a given sound source from peeking above a certain level. A compressor when set with the high ratio- 20:1 or infinity:1, will act as a limiter. A limiter is very helpful in broadcast television and music mastering. It sets a ceiling that can’t be passed. For tv, it can allow the producer to make their product as loud as it can be, without breaking fcc laws. It can help make their product stand out. In music production and music mastering a limiter will allow the music to be as loud as other recordings. How much compression and limiting should be used is a highly contested topic in music mastering, often referred to as the loudness wars. Compressing or limiting the audio signal so much that there is no dynamic range but rather a wall of sound creates a louder perceived volume. Next let's talk about gates. Gates are comparable to a compressor, which attenuates signals above a threshold, however, a gates attenuate signals that register below the threshold. Understanding these controls will help you use a compressor properly. There isn’t one way to compress signals, there are many. You can fry this fish five ways to sunday. Although there are starting points, how you compress a voice over today might differ tomorrow. This is mainly because the situations might be different, or you have a different need than before. Try out what has worked, try out what hasn’t. Being able to adapt the knowledge of how to operate the compressor/limiter to different situations will refine your ability to get the most out of your tools.
