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Compression and EQ Techniques for MIXING VOCALS

In this tutorial, we discuss how to work with Vocals and process them with Compression and EQ to help them sit better in a mix. We will also explain how to use signal flow in Pro Tools to help you apply effects and achieve a more balance sound in your music.

We discussed in our previous article how to achieve a balance of your recording by using Volume Automation to create "evenness" between the soft and loud parts of the vocal recording. Taking this process a step further, we will now concentrate on getting a "tone" in the vocals that sound pleasant in relation to the music. There is no right or wrong way to mix; sounds are dictated by the sounds around and the direction you want to go. Don't be afraid to experiment with these techniques and tools I am discussing here. Some of the most amazing things happen through experimentation.

Compression

Compressors can be one of the most difficult things to understand and use in the studio. Everyone has heard of them, we have all used them, as well as listen to other argue about which one is "better". In order to understand what we're dealing with better, let's look at what a compressor is and isn't.

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As a basic definition, a compressor is a device used to automatically the dynamic range of an audio signal, thereby resulting in a more "even" sound. (dynamic range is the distance between the softest and loudest sounds) The way in which a compressor achieves this "reduction" is dependent on what type of compressor and how man options it has. Most modern compressors have a common set of controls. Once you understand what they do, start experimenting with different compressor models to understand how they are different from one another.

Threshold - What is loud?

In order for a compressor to work, you need to tell it what is "loud" and what is "quiet". This is accomplished by setting the "Threshold" of the compressor. Any audio signal that passes (louder) than the Threshold will be compressed. If the audio signal never reaches the Threshold setting, it will NOT be compressed.

The Threshold setting is variable due to the fact that audio recording can be at various levels. For example, you can record a vocal part at a very low pre-amp level, thus making the entire audio signal softer. In this scenario you will likely need to turn down the Threshold quite a bit since the audio itself is very soft. On the opposite end of the spectrum, you can record a vocal part very loud with a lot of pre-amp gain. You'll likely lower the Threshold much less in this scenario due to the loudness of the recording.

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Notice in the picture above the "Threshold" knob on the left side of the Compressor. As you adjust the setting you will notice the yellow vertical line move to the left or right. This compressor plug-in is great because you can see the setting on the graph display.

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Only the audio signal that passes this "Threshold" setting will be compressed.

Ratio - How much should I turn it down?

Any signal that passes the Threshold will be reduced by the "Ratio" amount. For example, if the ratio is 2:1, you will get 1/2 the loudness out of the compressor. A ratio of 4:1 will yield 1/4 the loudness. Simple division, nothing too complicated. Since no two compressors are alike, you will notice a large amount of variation in "Ratio" setting between different models. Some models only go to a ratio of 20:1 while others can go as high as 100:1, or the ever popular "Nuke" setting on the Empirical Labs Distressor.

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Attack / Release - How quickly should I turn it down / up?

Once an audio signal passes the Threshold, the Attack setting tells it how quickly to bring the sound back down by the ratio. With a slower Attack setting, it will allow the louder "peaks" of the audio to come through before they are compressed. This can be very useful for drums, percussion, or vocals. On the other end of the equation is how quickly the compressor let's go of the audio signal once it falls below the Threshold, this is known as "Release". With a longer Release time, you can experience what is known as "pumping", which occurs when the compressor is still actively working and the next audio signal comes through. The compressor is trying to attack and release almost at the same time, producing an undesirable effect that sound like the sound is pumping up and down.

Make Up Gain - Boost the output

Due to the fact that compressor work by reducing the loudest peaks in the audio, it will naturally reduce the overall level of the audio coming out of the unit. Most compressors have a setting called "Make-Up Gain", which allows you to boost the overall output of the compressor, to "make-up" for the volume lost via the compression circuit. While there is no steadfast rule to using these features, a good point of reference is to look at how much volume you're losing and adjust the make-up gain to compensate for it. Example: if you reduce by -3db, boost the make-up gain by +3db

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Make-Up Gain located lower right side of unit

Go With The Signal Flow

One of the most common mistake people make when trying to understand compression is not taking into account signal flow of your audio. It's easy to get caught up in the "controls" of a compressor, however, for many professionals, it's more relevant to understand how the audio signal is "hitting" the compressor. In the previous article we discussed volume automation and how to create a consistent audio signal via automation. If you look at how the audio signal flows through Pro Tools (or a Tape Machine & Mixing Console), you'll see that the volume automation occurs after the compressor (or any insert) is applied.

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You'll notice in the diagram above that audio signal flows through the "Insert" points on a console before it hits the volume fader. In Pro Tools, as on most consoles, insert points are "Pre-Fader", meaning they are applied before the audio reaches the output. Many professional engineers prefer to do basic volume rides on the audio signal before it hits the compressor, allowing for better overall control of the tone & texture. If you think about it, you have audio signal that can be soft, loud, and everywhere in between, this can be quite "annoying" when you're trying to set your compressor. The audio signal is constantly jumping above and below the Threshold, hitting the Attack & Release circuit, generally making the compressor work really hard to maintain steady level. If we were to balance the differences in audio level before hitting the compressor, it won't have to work like a mad-man to keep everything nice and steady.

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Going back to our previous article on automation, if we apply volume automation on the vocal track before we send it through the compressor, we can wind up with a smoother, more cohesive signal. To achieve this we will utilize the bus architecture of Pro Tools along with Auxiliary Input Tracks (Aux).

Setting Up Auxiliary Input Via Bus Routing

You can easily create a new Aux Track in Pro Tools by going to the Track Menu, selecting New, and creating a new Mono Aux Track. Once it's created, most people like to place it next to the original vocal track. Route the output of the audio track trough any available Bus while also setting the input of the Aux track to match the same bus, thus completing the signal chain.

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Select any available bus output for the vocal track and make sure to set that same bus as the input on the Aux track you just created. This process allows you to apply the compressor on the Aux track, which is taking in signal from the volume rides on the audio track. You've created an audio path to allow very steady & precise control over your audio level, allowing you to use less of the compressor for hard-core "compression" and more for "tone and flavor". The audio signal has already been balance via the volume automation you created on the audio track. When this signal hits the compression circuit, it's no longer making the unit work hard to tame a wild audio signal, huffing & puffing it's way to infamy. You can focus on dialing in the compressor to give you a sonic "flavor" as opposed to it correcting mistakes.

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In the example above, the "VoxMain" audio track is feeding the aux track "Lead" via Bus 15. It also has volume automation written to the track adjusting it's level before it hits the McDSP Compressor on the aux track. You'll also notice that this particular compressor also has a built-in eq section to allow further shaping of the audio signal.

EQ or Compression - Which comes first?

There are many questions when it comes to mixing, none as perplexing as "what do I do first?" The good news is that there is no "right or wrong" when it comes to working with audio and processing, you can actually do whatever you want. Most professional engineers weigh a lot of different things in their mind when they approach a mix. Most of the time, the approach starts by looking/listening to all the different elements in the song and trying to figure out what needs to be removed in order to allow the parts to blend together in a cohesive fashion. The majority of this work is accomplished by eq's, which allow you to manipulate the frequencies by boosting or cutting them from the audio signal. You can think of them as a way to "sculpt" the sounds so they blend well together.

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Avid Channel Strip plug-in

Due to the signal path we have already discussed, if we place the eq on directly on the vocal track it will be applied in line before the compressor circuit. If we apply the eq after the compressor, we will be eq'ing the signal after it's gone through the compression circuit. Due to the ever changing nature of audio different types of voices and sounds, most engineers actually use a combination of pre & post compression eq to achieve a balanced signal.

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The above example shows a vocal track with an eq placed on it directly, routed through a bus into an aux track that has a compressor followed by another eq. This shows a typical vocal chain which utilized volume automation, bus routing, and plug-in processing pre & post fader.

One of the best things to take away from this is recognizing how the various functions of Pro Tools, or any console, are used together to achieve a specific end result. There is no magic "mix it now" button that will make you sound like a superstar. Challenge yourself by practicing these techniques as if they were an instrument. You'll develop your own taste and distinct sound as you figure out ways to incorporate different techniques into your music or studio project. Throughout my career with my band, Dub Pistols, we learned and used many different techniques from many different engineers, each one unique in it's own way.

Jason O'Bryan (Dub Pistols)


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