<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span class="tab">Hi,</span></div><div><br><span class="tab"></span></div><div><span class="tab">I'm trying to design or find a resonant lowpass filter for use with libPd for Openframeworks running on an iPhone 4.</span></div><div><span class="tab"><br></span></div><div><span class="tab">1. I've tried the rjlib filter attached (filtertest_list.tar.gz) and it works fine in Pd, but instantly breaks when I run it on the iPhone - all other playing audio cuts out, and it is impossible to reset. I suspect that the buffers fb1 fb2 ff1 ff2 ff3 are hitting NAN values and staying there, but I haven't tested this.</span></div><div><br><span class="tab"></span></div><div><span class="tab">2. I've had a go at implementing the filter from http://www.musicdsp.org/archive.php?classid=3#25 as a Pd external (mvcf~.tar.gz) and it is very
efficient CPU-wise. However, higher values of f or q cause the internal filter buffers to hit NAN and stay there (tested in Pd - I haven't tried this on the iPhone yet).</span></div><div><br><span class="tab"></span></div><div><span class="tab">I would ideally like to find out why the second attempt breaks at high q and/or f, as what I want is a 24dB/Octave moog-ish filter. I'm sure those of you with higher math skills will intuitively know why, but I'm just learning calculus now (my early education was a bit chaotic). I'm also limited by the fact that this is for a commercial project (although I'll be happy to share the code :) so I can't just take a GPL external and recompiled libpd with it.<br></span></div><div> <br>Ed<br><br></div><div>Gemnotes-0.1alpha: Live music notation for Pure Data<br>http://sharktracks.co.uk/</div></div></body></html>