http://www.wiretotheear.com/2012/07/31/drum-machine-history/
http://www.synthfool.com/docs/Roland/TR_Series/Roland%20TR-909%20Owners%20Manual.pdf
http://errozero.co.uk/acid-machine/
http://www.soundonsound.com/sos/dec04/articles/roland.htm
http://www.youtube.com/watch?v=icOrGNHGkIA
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