<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 31, 2017, at 2:42 PM, Walker Shurlds <<a href="mailto:walkershurlds@gmail.com" class="">walkershurlds@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div name="messageBodySection" class="">In theory, I would think you could follow up a two pole LP with two differentiators, and you'd have the right transfer function for a two pole HP. Same for four, with four differentiators. Differentiators tend to be impractical though–I wonder if this has been tried.<br class=""></div></div></div></blockquote><div><br class=""></div><div>Quick answer: </div><div><br class=""></div><div>No, no, no, no, no.</div><div><br class=""></div><div>More helpful answer:</div><div><br class=""></div><div>First off, you're going to need to tune those four differentiators to track the ladder filter.</div><div><br class=""></div><div>So that would effectively be a filter on it's own, similar to the Moog high pass filter.</div><div><br class=""></div><div>If your ladder filter is tuned to a frequency of, say 100Hz, then at 1kHz the signal will be down 80dB, and at 10kHz the signal will be down 160dB. So your differentiators would need a gain of 100 million at the high end to bring the signal back up. </div><div><br class=""></div><div>That's a crazy amount of gain. The tiniest noise would be amplified to clipping.</div><div><br class=""></div><div> -- Don</div></div><div apple-content-edited="true" class="">
<div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-variant: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><font face="Monaco" class=""><span style="font-size: 11px;" class="">--</span></font></div><div class=""><font face="Monaco" class=""><span style="font-size: 11px;" class="">Donald Tillman, </span></font><span style="font-size: 11px; font-family: Monaco;" class="">Palo Alto, California</span></div><div class=""><span style="font-size: 11px; font-family: Monaco;" class=""><a href="http://www.till.com" class="">http://www.till.com</a></span></div><div class=""><font face="Monaco" class=""><span style="font-size: 11px;" class=""><br class=""></span></font></div></div></span></div></span></div></div></div></div></div><br class="Apple-interchange-newline">
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