oooooooooo.... What does this button do?

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Have wanted my own MS20 ever since I got a chance to play with one about 9 years ago. My studio colleague has an MS20, it' here as well, but I was very reluctant to really play around with it ... never dick with another man's vintage synth :) I'm still on the lookout for an ARP2600 or a Macbeth M5N, but both of those run into several thousands, and in the case of the ARP it had better be mint condition because HK is the wrong place to get these things repaired. Just wish I had motivation to do something with all this gear ... The way I feel about music production lately I should just open this place up as a museum.