<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">You could have a look at Antti’s Powerwave synth paper from DAFX 05. It’s an FPGA-based synth that uses a Moog-model for the filter if I remember. That’s a much simpler structure than an SVF. Furthermore, the Powerwave uses pole-mixing (a la Xpander) to provide multiple different responses. After all, in the digital realm, there’s really no reason not to.<div class=""><br class=""></div><div class="">Aside from that, the Ear Level Engineering site is good:</div><div class=""><br class=""></div><div class=""><a href="http://www.earlevel.com/main/category/synthesizers/" class="">http://www.earlevel.com/main/category/synthesizers/</a></div><div class=""><br class=""></div><div class="">..and that links to Vadim Zavalishin’s "THE ART OF VA FILTER DESIGN”:</div><div class=""><br class=""></div><div class=""><a href="https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf" class="">https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf</a></div><div class=""><br class=""></div><div class=""><br class=""><div class="">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 2 May 2018, at 19:51, Scott Gravenhorst <<a href="mailto:music.maker@gte.net" class="">music.maker@gte.net</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class="">Hi List,<br class=""><br class="">I'm looking for information on digital 4 pole filters. I need to be able<br class="">to control Q and Fc. Among the many documents I found with google was this<br class="">document:<br class=""><br class=""><a href="http://www.rane.com/pdf/linriley.pdf" class="">http://www.rane.com/pdf/linriley.pdf</a> <br class=""><br class="">which describes an analog version of a 4th order state variable filter, but<br class="">my math lessons were so many years ago, that it's not entirely helpful. On<br class="">page 4 the document shows how the resistors are to be given values (right<br class="">side) for a Linkwitz-Riley crossover. I have a feeling this is close to<br class="">what I want, but <br class=""><br class="">1) I'm unable to determine how to change the filter so that I can control Q<br class="">and Fc.<br class="">2) I'm unable to convert this to a block diagram representation of the same<br class="">circuit as a digital model.<br class="">3) Information on how to tap the structure for modes other than lowpass<br class="">would be very helpful.<br class=""><br class="">I'm familiar with the 2nd order state variable filter, but expanding that<br class="">by adding two more integrators is not all that simple to my eyes. I can<br class="">see from the Linkwitz-Riley circuit that each integrator has a negative<br class="">feedback path.<br class=""><br class="">I would also be interested in other 4 pole filter topolgies where access is<br class="">given for Q and Fc control parameters.<br class=""><br class="">I would be extremely grateful for pointers to readings and information<br class="">helpful in this quest.<br class=""><br class="">-- ScottG<br class="">________________________________________________________________________<br class="">-- Scott Gravenhorst<br class="">-- <a href="http://scott.joviansynth.com/" class="">http://scott.joviansynth.com/</a><br class="">-- When the going gets tough, the tough use the command line.<br class="">-- Matt 21:22<br class=""><br class="">_______________________________________________<br class="">Synth-diy mailing list<br class=""><a href="mailto:Synth-diy@synth-diy.org" class="">Synth-diy@synth-diy.org</a><br class="">http://synth-diy.org/mailman/listinfo/synth-diy<br class=""></div></div></blockquote></div><br class=""></div></body></html>