Using pitch, delay and modulation effects to perceptually spread a mono source across additional, adjacent playback channels is a staple of music production, born in stereo and extended to immersive. This tutorial begins with the historical origins of the effect in the mid 1970s, showing the signal processing chains used, measuring its impact on the signal, discussing its psychoacoustic merit, and demonstrating the resulting sound. The evolution from stereo through surround sound to immersive formats using contemporary production tools and techniques is demonstrated. The effect is still evolving as new tools are developed and creators explore what is possible across all immersive artforms – music, AR/VR, and games. It is hoped a deep dive into the first 50 years of this effect will inform and inspire immersive mixers for the future.
