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Mastering Elements Part 1: The Buss Compressor

This post is part of a series called Creative Session: All About Compression.
5 Compression Techniques and How to Use Them
Create a Parallel Compression Bus in Logic Pro 8

Mastering is a pretty big subject, so instead of tackling it in one tutorial I thought it might be easier, for those new to the subject, if I split it up into bite sized pieces. Each tutorial will look at a separate process used in a typical mastering set up, why we use it and what it achieves.

One of the first processors used in any mastering chain is a buss compressor, this is really just a name for compressor used to treat an entire mix (i.e. the master buss). Let's take a closer look at how the compressor is used in mastering and the different processors used for the task.

1. The Mastering Compressor's Job

When we use any compressor whether it's in our mix, live on stage or in our mastering chain, we tend to have one aim and thats to reduce dynamic range. Although large reductions in dynamic range are often seen as a bad thing, sensible amounts of dynamic treatment can produce excellent results, especially in mastering.

Without delving too far into the loudness/dynamics argument (there will a tutorial on this later), it's safe to say that the key to using any dynamics processor on your master output is restraint. With the plug-ins available to just about any user, extreme levels of compression, limiting and therefore loudness are right at our fingertips but that doesn't mean everything should be turned up to 11.

When you have finished your final mix it's more than likely to contain loud and quiet sections and some instruments may feel a little disconnected. These issues can often be fixed in the mix and if you get the chance this is the best way to tackle them. Failing that compression can certainly help bring these problem areas into line.

Buss compression can result in an even dynamic signature.

So with the right settings a buss compressor can make the differences between loud and quiet sections smaller, add cohesion to separate instruments in the mix, reduce unwanted peaks and generally lower our dynamic range, allowing further processors to create high perceived loudness.

We'll also take a look at how different models of compressor can impart character and tone to your master. This may effect your choice of processor so it's an important aspect of mastering compression.

2. Weapon of Choice

To some the right choice of mastering compressor is essential, to others it's more about the correct settings. If you are a beginner in the field of mastering it's wise not to focus too much on which specific product you go with and concentrate on the technique being used.

Pros tend to go with hardware or high end plug-ins for mastering duties. Many of the software products use physical and component modelling to emulate their hardware cousins and they often do an excellent job. Component modelling involves someone in a white coat spending hours measuring the signal at each stage of the hardware processor and then recreating it in the form of a digital algorithm, which can ultimately run in plug-in form. Rather them than me!!

You may be wondering why go to all this trouble to recreate some old piece of analog kit when we have perfectly good 100% digital compressors residing in our DAWs plug-in library. The answer generally comes down to what some of us would call 'fatness' or 'warmth'. These terms are often attached to tube or transistor based hardware processors and this is what makes them so sought after.

In reality these terms don't mean a huge amount and something that is 'fat' or 'warm' is probably just saturated, modulated or slightly out of phase. Analog circuitry tends to add random anomalies and variations that trick our ears into believing that we are hearing something 'better' than the original signal. Of course this is a subjective subject, so if you like what you are hearing then thats what counts. In the words of the great Joe Meek "if it sounds right, it is right!".

So to put it in basic terms if you want to add flavour and character to your master then you will want to go with a vintage emulation, if you are after something a little more transparent then stick with a good quality digital compressor plug-in. (Of course they are all digital but I'm sure you get the picture).

Most DAWs supply perfectly passable compressors as standard and some are even starting to include physically modelled processors. Propellerhead's Record for example now features a reproduction of the legendary SSL master buss compressor on its main mixer. Truly excellent results can be achieved here with no plug-ins in sight.

Here are a few examples of a track compressed with various compressors, remember this is subtle stuff so you may need to listen carefully to hear the differences. First up a few stock digital plug-in models...

Ableton's stock compressor.

An unmastered track being treated by Ableton's stock compressor.

Logic's standard compressor using the original Platinum model.

The audio being fed through Logic's compressor.

And now a few from plug-ins that are modelled on hard ware ...

Record's SSL modelled master buss compressor.

The pre master is fed through the Record master buss compressor.

The T-Racks 3 model 670 vintage compressor.

The master is finally fed through the T-Racks model 670 with a good amount of gain.

3. The Order of Things

Some of you who are building your first custom mastering chains may be a little confused as to where you should place your mastering compressor. In most cases it's pretty wise to have the main compressor right at the start of the chain, this way any wayward peaks will be caught immediately. There are some circumstances when placing a compressor later in the chain might be advisable though.

In some situations even a good buss compressor may not reduce the dynamic range of your tracks satisfactorily and you may find the need for a second processor later in the chain. In this situation you may want to place another compressor after any EQ or other effects. This second round of compression should do well in catching any remaining peaks and you should find this approach is much more effective than simply increasing the intensity of the original compressor.

Cascading compressors can help attack problem areas in your mix.

4. Crucial Settings

When it comes to dialling the correct settings for your buss compressor, subtlety really is the key. In most cases we are looking for a clear, transparent sound with no real evidence that the sound is being compressed at all. To achieve this transparency we need to think in terms or broad, light brush strokes anything too severe and you'll get pumping effects and other unwanted artefacts.

First of all concentrate on the compressors ratio and threshold settings. Set your ratio low, this is really important and part of the traditional buss compressors natural characteristic. This low threshold setting will mean that no drastic gain reduction occurs and that any processing is minimal. You can then start to bring your threshold down until any peaks are being reduced.

Low ratios are a must if you want to achieve transparent compression.

With these two parameters set, you can start to think about attack and release times. If in doubt here set them to very long/high values and go from there. In the words of a mentor of mine, he yearned for a mastering compressor that had attack and release times of 'forever', so this goes some way to let you know what you should be aiming for here. These long times will enable you to get super transparent results.

Long attack and release times will help to reduce unwanted pumping effects.

5. Intense Compression and Parallel Processing

On occasion you may want to 'smash' a track and give it a pumped up feel. This can add energy and make a denser louder master. It's more of a creative effect that a mastering tool but there is a time and place for this sort of approach and you shouldn't rule it out, in fact it's the basis of some peoples sound.

There are few ways to achieve this overly compressed sound. One is to use a parallel compression set up, this is pretty easy and simply involved copying your original track and treating it ... well ... in parallel! With your duplicate track created you can apply some seriously heavy compression and mix this compressed track to taste with your original. This approach gives you loads of control and the squashed sound you might be after. Some compressors offer a 'mix' function, allowing parallel compression to be performed directly from the within the plug-in.

Parallel compression set ups can allow intense compression to be controlled.

6. M/S Processing and Multiband Dynamics

There are some parameters you may see on mastering compressors that I've not covered here. A few of these may include M/S processing options and multi-band operation. Most multi-band compressors will come as a separate processor but is a certainly a plug-in you might use in your chain.

Don't worry about these compression characteristics just yet as I'll be covering them in future mastering tutorials and I'll go through them in detail.

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