Stereo Width Control is an Audio Unit plugin designed for iPhone users. It allows for manipulation of stereo width across 4 adjustable frequency bands. This tool is particularly useful for mastering engineers aiming to maintain precise focus in the center channel for bass frequencies while creating a spacious stereo image in the mid-range frequencies.

With the ability to operate with 1 to 4 separate bands, users can solo each band for individual adjustments in frequency range and stereo width settings. Additionally, a stereo vectorscope graph in the interface aids in visualizing track volume and stereo width effectively.

Please note that Stereo Width Control functions as an Audio Unit plugin within host applications like GarageBand, requiring integration for audio processing.