This video, via mastering engineer Ian Shepherd, takes a look at how to monitor, measure and modify stereo width in the mastering process. 

Along the way, Shepherd discusses:

• How to measure the stereo width of your mix
• What it sounds like when there is too much (or too little) stereo width in your audio
• Why you should never use the “polarity flip” trick to try and get more width in your mix
• Another two much more powerful & sophisticated ways to analyze the stereo image and phase content of your master
• A way to take detailed control of the phase coherence of your audio – and when you shouldn’t use it

If you’ve got other tips for working with stereo width, share it in the comments!