Roger Waters’ EMS VCS3 Filter Sweep on ‘When You’re In’ from *Obscured by Clouds*

On Pink Floyd’s 1972 film soundtrack Obscured by Clouds, the EMS VCS3 (a cousin of the Synthi A) gets plenty of airtime, but its most rhythmic use comes on “When You’re In.” Roger Waters patched the VCS3 to produce a slow, sweeping low‑pass filter that rises and falls in lockstep with the drum pattern. The effect sounds almost like a second percussion element — a breathing, mechanical whoosh that accents the off‑beats.

During sessions at Strawberry Studios in Château d’Hérouville, France, the band tracked the rhythm section live in the main room. Nick Mason’s drums and a simple bass line were recorded to tape, then Waters overdubbed the VCS3 in real time, manually turning the filter frequency knob to match the tempo. No sequencer was used — just Waters’ hand on the synth, riding the cutoff while listening to the playback through headphones. The result is a subtle but constant texture that pushes the track forward without overwhelming the acoustic guitar and vocal.