Roland SDD-320 Dimension D

The Roland SDD-320 Dimension D is a stereo analog rack effect released in 1979, built to take a high-quality version of the chorus sound to the studio world¹². Rather than the obvious sweep of a conventional chorus pedal, it produces a subtle widening and thickening: Delicious Audio describes it as "an effect that created a unique stereo modulation that can be mistaken for a chorus… Though time-based like a chorus, the Dimension's circuit is quite unique and sophisticated, subtly enhancing the width and depth of the source audio without any prominent modulated movement."³

Boss calls it "a legendary studio rack effect heard on countless hit records," and says that very quickly after its 1979 debut it "became a go-to secret weapon for audio engineers and music producers around the world"⁴. On That Pedal Show, the hosts note it "quickly became a staple of studio recording for its lush, thickening modulation effect"².

How it works and how it is controlled

The circuit used BBDs (bucket brigade devices) in two independent delay lines, out of phase, blended with a dry signal. Dave Hunter, writing in GuitarPlayer, explains this created "a sound that was less motion and more dimension, totally avoiding the more obvious and occasionally obtrusive wobble of chorus effects designed more for depth and speed"¹.

Operation is unusually simple for a rack unit: four preset buttons, each a fixed setting with increasing width and depth³⁶. Because it was made for studios, it also allows pressing two buttons together for additional variations, something the compact Dimension C pedal does not do².

Where it sits in Roland's history

Roland released the SDD-320 in 1979, alongside a lineage of chorus products that includes the JC-120 Jazz Chorus amplifier and the Boss CE-1 Chorus Ensemble⁴⁵. The rack version became highly sought after³, and it was used extensively during the 1980s by many icons of that era⁷. Documented users include Brian Eno, Talking Heads, Kate Bush and U2⁶⁸.

Premier Guitar records one notable guitar use: "Stevie Ray Vaughan fell in love with the sound of the Dimension D when he worked with Nile Rogers and David Bowie on Let's Dance, and it became one of his secret studio weapons, used in the mixing stage to subtly widen his guitar on solos."⁹

The Dimension C and other descendants

Roland put the essence of the SDD-320 into the compact Boss DC-2 Dimension C pedal in 1985. On That Pedal Show, Mick and Dan compared the two: "the dimension D has its built-in noise reduction it's it's made for studios and also made for line level specifically it has microphone inputs on it where is the dimension C is specifically for guitar."²

Boss states the Dimension D "was designed as a studio effect that supported either mono or stereo input sources, the DC-2 was specifically created for mono sources like guitar, and features a modified circuit that produces a Dimension effect with a slightly different tonal flavor"⁴.

The sound has since been carried forward in several forms:

• Boss DC-2w Dimension C: a pedal that emulates and updates the rack unit, recreating the original four presets "which provide sonic variations with increasing width and depth"³
• Boss MD-500: a modeler whose Dimension mode "Models the legendary Roland SDD-320 Dimension D rack unit"⁷
• Fromel Seraph Deluxe: a stereo analog dimensional chorus modeled after the SDD-320⁸
• Klark Teknik 3rd Dimension BBD-320: a 2U rack clone of the Dimension D⁵

Gearnews noted of the Klark Teknik clone that "Just like the Dimension D, the 3rd Dimension BBD-320 is a 2U rack unit, which is as excessive now as it was in 1980, considering the handful of buttons gracing the front panel and the limited number of components inside"⁵⁷.

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