When it comes to mastering treatments stereo enhancement is a tricky one. Beginners often make the mistake of overusing it or using the wrong plug-ins for the job. The good news is, with the right technique in place, there is a place for stereo processing in your mastering chain.
In this tutorial I'll go through a few examples of different stereo processing that can be used in mastering and highlight some of the pitfalls that you might come across. I've tried to cover processors from as many different DAWs and manufacturers as possible.
Step 1: What to Avoid
The main thing that presents a problem when it comes to stereo treatment in mastering is the use of the wrong processor. Many DAWs supply stereo enhancement tools that are perfectly usable in the mix but are not really suited to a mastering environment.
The majority of these 'mix' processors are single band in nature, meaning that they treat the entire frequency range indiscriminately. This leads to a situation where we are processing parts of our mix that should remain untouched.
In most cases it's our low end that should remain intact and that is something our single band plug-ins just aren't capable of. Below are a few examples of the sort of processors I'm referring to and our example track processed by them.
The untreated example clip.
The untreated recording.
The Cubase stereo enhancer.
... and treated with the Cubase single band enhancer.
In this example the stereo widening is pretty impressive but the low end mix has been threatened and loses is clarity and focus.
Step 2: The Subtle Approach
If you are a firm part of the 'less is more' camp then you may want to take the subtle approach to stereo enhancement. A simple linear phase equaliser can be enough to make your masters sound a little wider.
Before you apply any other mastering processors, duplicate your exported track and place it on two tracks in your chosen DAW. Pan one hard left and the other hard right. Now apply a mastering grade EQ to each channel. You can now apply different EQ settings to each side of your master.
Avoid working on lower frequencies here and concentrate on high mids and high frequency. Also keep Q values low to avoid coloration and hype. So for instance add a few db of high frequency in one side and remove a few db of the same frequency in the other.
Of course this will work better in some situation than in others. It can be a great way of adding some width to older recordings that perhaps lack a great stereo image. If you find the EQ adds too much coloration, you can also try the same technique using very slightly different compression values in each side.
Two linear phase EQs providing stereo enhancement.
The audio with some subtle EQ based widening.
The duplicate channels panned hard.
Step 3: Dedicated Mastering Enhancement
Using a dedicated stereo mastering processor is probably the most popular route to achieving a wider image. There are many to choose from but the main thing to look out for is a frequency dependant interface.
Logic provides a frequency specific enhancer
As does Reson / Record.
To give you an example of what I mean check out the stereo enhancer included in isotope's Ozone processor. Many DAWs include stereo processors suitable for mastering as well. Logic Pro 9's enhancer, for example, is capable of effecting only certain frequencies.
Izotope Ozone's fully features stereo enhancement area
The audio is treated by Ozone.
Step 4: Parallel Tricks
There are some situations where more intense stereo processes can be used in mastering but some know how is required here. Setting up a parallel buss in your mastering project will allow you to apply pretty much any process to your parallel mix, without adversely effecting your final master.
With a second version of you mix set up you can apply even single band enhancement and mix to taste. Even in this situation it's a good idea to filter the low end from the secondary stream to ensure that you don't create a confused and incoherent low end mix.
This technique can also be used to add extra compression an limiting during the mastering process. In general parallel processing during mastering will create a much denser, louder result with a vastly reduced dynamic range, so if this is not what your after you may want to look at other options.
A parallel mastering buss set up in Cubase 5
The audio is given added stereo width in Cubase.
Step 5: M/S Technology
Using M/S based processors is a great way to enhance the stereo content in your mix and it's also extremely transparent (and mono compatible!). If you are unsure what M/S processing is then you might want to have a quick read of my in depth tutorial on the subject... here.
You can route your own M/S processing set ups or use a dedicated plug-in. The latter is certainly the easier route but you will have to invest in the right plug-in and they aren't cheap. Brainworx do make some really excellent products in this area.
Using M/S processing you can manipulate the mono and stereo data in your mix separately and not only enhance the stereo width but also force the lower frequencies to become mono. Extremely useful stuff!
The fantastic Brainworx 'bx_digital V2'
The file is treated to some M/S processing.
Step 6: Reverb on Your Master Anyone?
Now this is a bit of a strange one but some mastering processors do supply a mastering reverb section. Izotope's Ozone has one and it's certainly something that will supply a wider stereo feel, saying that I'm not 100% convinced on this one and would probably only reserve it to old recordings that needed restoration or a new lease of life.
All this said, I would never write off a technique, as what I may find strange someone else might swear by! So I would certainly look into it and see if its for you.
The mastering reverb section of the Izotope Ozone suite
Ozone's reverb is added.