UM225 / UM226

The Waves UM225 and UM226 are purpose-built upmixing plugins designed to convert stereo source material into 5.0 or 5.1 surround formats with genuine musicality. Rather than relying on simple matrix decoding or phase manipulation, these tools employ eight distinct algorithms that intelligently distribute frequency content and transient information across the surround field, making them considerably more sophisticated than legacy upmixing approaches.

The sonic architecture centers on separating program material into discrete components - ambient information spreads to surround channels while punch and transient detail remains anchored to the fronts. The Ambience control adjusts how diffusely the surround stage expands, critical for preventing hyper-localized artifacts that plague naive upmixing. The Punch control similarly manages how aggressively transients fan across the stereo plane, preserving mix focus without creating unnaturally wide imaging.

The UM226 adds a dedicated LFE channel with fourth-order filtering plus LoAir, an octave-lower harmonic generator that adds controlled low-frequency texture without requiring subwoofer content in the original stereo mix. Output trims for each speaker stage enable corrective mixing, essential when the upmix requires integration with existing surround elements.

These plugins find their strongest application in broadcast, post-production, and archival work where converting stereo masters to surround is required without remixing from stems. The independent surround and stereo paths also function for pure stereo widening and enhancement, though dedicated stereo processors handle this task more elegantly. Among surround upmixers, the UM series represents one of the more transparent, controllable options available.