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"The PLL is an analog harmonizer that turns your input signal into a square wave and then has a multiplier and divider that adds intervals to your note. "
more info here
there is an PLL drone available too.
be sure to visit schumann electronics.com
Anything CAN be music, but it doesn't BECOME MUSIC until someone WILLS it to be music,
and the audience listening to it decides to PERCEIVE IT AS MUSIC.
(Frank Zappa)