<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">On Aug 22, 2019, at 6:07 PM, Tom Wiltshire <<a href="mailto:tom@electricdruid.net" class="">tom@electricdruid.net</a>> wrote:<br class=""><div><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><div class="">[...] And the State Variable makes a reasonable appearance by virtue of its versatility, but is more common in modular synths than in any classic keyboard.As we know, Oberheim was the only manufacturer who pushed 2-pole filters, and even then the later instruments offered that as an option, not the only choice. </div></div></blockquote><div><br class=""></div><div>The State Variable Filter was introduced by the brilliant Dennis Colin in the ARP 2500 VCF. And his article is one of the classics:</div><div><br class=""></div><div> Dennis Colin</div><div> The Electrical Design and Musical Applications of an Unconditionally Stable Combination Voltage Controlled Highpass, Bandpass, Lowpass, Band Reject Filter/Resonator</div><div> Journal of the Audio Engineering Society, Dec 1971</div><div> <a href="http://www.guitarfool.com/ARP2500/DennisCollinPaper.pdf" class="">http://www.guitarfool.com/ARP2500/DennisCollinPaper.pdf</a></div><div><br class=""></div><div>He didn't invent the SVF, but he was the first to voltage control it and apply it to music.</div><div><br class=""></div><div>The State Variable Filter has a long history, back to analog computers. It's also the same mechanism as the simple harmonic motion of a mass, spring, and friction. So it has a wonderful "universal" quality.</div><div><br class=""></div><div>The Oberheim filter, the Rhodes Chroma filter, and others, are mostly variations on this.</div></div><div class="">
<div style="color: rgb(0, 0, 0); font-family: Menlo; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;"><br class=""> -- Don<br class="">--<br class="">Donald Tillman, Palo Alto, California<br class=""><a href="http://www.till.com" class="">http://www.till.com</a></div>
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