Stereo imagers are the easiest way to expand your stereo image and make your recordings sound wider - however, they also introduce the most phase cancellation. Using a dedicated stereo image plugin may be okay on an instrument but it’s best to avoid it when mastering a full mix.
Stereo imagers introduce various forms of phase cancellation to expand the image. Occasionally, the left track and right track are blended together in a way that causes cancellation and subsequent stereo expansion .
More often, some form of delay is used to cause this phase cancellation. When using delay-based stereo expansion, the signal can quickly become unfocused and washed out sounding, resulting in a mix that has lost most of its impact.
Although upward compression isn’t too common of an effect, it can be used in combination with mid-side processing to greatly impact the width of your stereo image in a beneficial way. One plugin that offers both upward compression and mid-side processing is Boost by Ursa DSP.
If you switch the plugin to the mid-side mode in the top right, you are now affecting the signal as mid and side instead of left and right.
If we increase the focus function and alter the priority slider to the side, we’ve caused upward compression to occur on the side image. In turn, the details of the side image will be brought forward and made louder. This amplifies the side image, in turn expanding the stereo image.
If you’re new to mid-side imaging, mid-side equalization is the best way to get started - with it you can expand your stereo image by increasing the side image’s amplitude or decreasing the mid image’s amplitude. Mid-side equalization also allows for frequency-specific stereo expansion.
For example, say I want 1kHz to be a little wider. I could create a bell filter at 1kHz and then boost this frequency. The same goes for the high frequencies, where I could make a shelf and expand the air of the master - this is personally one of my favorite things to do to a master.
Similarly, if I was to reduce a part of the mid image, I’ve made that frequency louder comparatively on the side image.
Mid-side saturation isn’t super-common, but will probably become a more commonplace processor in the near future - it offers an incredibly useful way to simultaneously cause expansion and saturation. This results in a complex sound that’s a lot more unique than a lot of typical stereo imagers.
The only processor I’ve used that allows for this is the FabFilter Saturn and Saturn 2, but if you know of more with this capability let me know.
Similar to mid-side equalization or upward compression, adding saturation or distortion to the side image increases its amplitude, in turn making a master wider.
Using multiple bands, you can make this expansion frequency-specific - and even dynamic using the program-dependent functionality.
Mid-side compression creates a dynamic relationship between your mid and side image, in turn causing natural-sounding stereo expansion. Whenever the mid-channel gets compressed, the side channel will have a louder amplitude in comparison - resulting in a signal that’s wider during compression.
Whereas mid-side equalization lets you control the frequency range of your stereo expansion, mid-side compression or limiting lets you control the timing of your stereo expansion.
The longer your release time, the longer the mid-channel will be compressed, and the longer the side image will be louder in comparison to the mid-channel.
A shorter release time will result in more dynamic stereo expansion, a longer one in more consistent stereo expansion.
Expansion is another way to add a dynamic element to your stereo imaging - depending on the processor that you use, you can make your expansion both frequency-specific and dynamic or time-specific. A multi-band expander is probably the best choice, but a dynamic equalizer will work well.
Using the FabFilter Multi-band plugin, we can create bands and alter the settings from compression to expansion, determine the range, and set the correct threshold. Then we can make these bands occur on the mid or side image.
By adjusting the attack and release times, we can make this expansion have a timing aspect to it, and either has the expansion last for a longer or shorter amount of time.
Tape machine stereo expansion is really unique and interesting, in that the majority of the ways stereo expansion occurs is caused by some unwanted effect or technical error. If your tape machine has asperity and crosstalk functionality, you can create this unique form of analog stereo expansion.
Asperity refers to imperfections in the surface of the tape that results in a very high-frequency distortion. Since this noise is stereo, it can have a mild stereo imaging effect - use it sparingly though to avoid a noisy master.
Crosstalk occurs when the left and right channels bled into one another - this glues the sound together but also causes mild phase cancellation and expansion. More crosstalk doesn’t necessarily mean greater expansion so listen closely for the right spot.
