Andy Johns' Leslie Speaker Miking Technique on 'Can't You Hear Me Knocking'

The swirly, almost warbling guitar intro to “Can’t You Hear Me Knocking” wasn’t just a pedal — it was engineer Andy Johns running Keith Richards’ Gibson Les Paul through a Leslie speaker cabinet normally reserved for a Hammond organ. The Leslie’s rotating horn and bass rotor create a natural Doppler shift, but Johns took it further by placing two microphones: one aimed at the upper rotating horn, the other at the stationary lower rotor.

Johns then panned those two mics hard left and right during the mix, so the spin literally swims across the stereo field. It’s the same trick you’d use to make an organ sound like it’s rotating around the room, but on a raw rock riff it sounds almost psychedelic. Richards reportedly just played the riff straight — no vibrato — and let the spinning cabinet do all the work.