‘Pseudo-stereo’ plugins use under-the-hood delays, comb filtering, reverb, detuning and DSP wizardry to create completely new stereo information. Adding this kind of stereo width can be dangerous in a mix, especially if you go heavy across lots of sounds – but when applied correctly, stereoisation can hugely help one or two elements jump right out of the mix.
There are stacks of widening plugins out there to try, so the only way to see which ones suit your style of mixing (and the sound in question) is to test them out. Being able to restrict the frequency content of the width is massively helpful, which is why iZotope’s multiband Ozone 8 Imager is one of the best out there. Other great options include the free version of Ozone 8 Imager, Plugin Boutique’s StereoSavage, Soundtoys MicroShift and JST’s SideWidener, free in Plugins.
Pseudo-widening tools such as StereoSavage allow you to ‘stereoise’ narrow signals