Getting to talk about ELP and other prog is definitely one of the things I miss from the old site.
The keyboard you’re seeing him abuse is a Hammond L-100. It’s a type of tonewheel organ, meaning it actually has a set of mechanically spinning discs inside that generate the sounds of each note. It’s a technology that dates back to the 1930s when it wasn’t economical to make tones for an entire keyboard from electronic circuits. So when you see him fiddling with the switch and making that long, dipping howl, he’s actually switching off and on the motor driving the tonewheels making them slow down and speed back up again.
The organ also incorporates a spring reverb, which is another electromechanical solution from the pre-digital world. The sound is actually driven through a set of physical springs inside the organ, and the wiggling of the springs results in a reverb-like sound in the final output. That crashing sound you hear when he’s throwing it on the ground and putting his hands in the back of it is the sound of those springs being physically knocked around and moved way outside the range of what they’d usually see from just audio signal.
That organ’s job was to get beat up every night on stage. The keyboard tech would fix it up every time and replace whatever was broken. You’ll even see where it’s been repaired and reinforced with steel plates. On the other side he had a Hammond C3, which was a much nicer tonewheel organ that didn’t get as abused.
That computer with wings at the end of Karn Evil 9? That thing is the Moog synthesizer.