Stereo width is created through several techniques: panning individual layers to different positions, using unison detune on synthesizers, applying stereo widening plugins, or using mid-side processing to enhance or reduce the side channel independently of the mono center.
A key principle in EDM mixing is keeping low frequencies mono. Bass energy below 200 Hz is non-directional and causes phase cancellation problems when played in mono (clubs, phone speakers). Keeping kick and bass centered preserves punch and prevents mud.
The upper frequencies—supersaws, pads, hi-hats, and effects—benefit from wide stereo treatment to create the sense of space that makes EDM feel large and immersive on a system. Tools like iZotope Imager, Ozone's Stereo Widener, or FL Studio's Fruity Stereo Enhancer let you control width by frequency band.