Hi Ed,<div><br></div><div>I just tested your filtertest_list patch in RjDj and it worked exactly as expected. As Rich suggested maybe you&#39;re using an outdated version of libpd?</div><div><br></div><div>If Frank&#39;s around I&#39;m sure he would know for certain but if I remember rightly the [u_lowpass] / [u_beequad] combination is not really designed for dynamically changing parameters. Maybe take a look at [e_reslop], [e_lop2] and [e_lop4] for some other filter implementations. </div>

<div><br></div><div>Regarding your second attempt, at what frequency does it &#39;break&#39; and what&#39;s your sampling rate?</div><div><br></div><div>Cheers,</div><div>Joe<br><br><div class="gmail_quote">On 20 March 2012 05:57, Ed Kelly <span dir="ltr">&lt;<a href="mailto:morph_2016@yahoo.co.uk">morph_2016@yahoo.co.uk</a>&gt;</span> wrote:<br>

<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-size:12pt;font-family:times new roman,new york,times,serif"><div><span>Hi,</span></div><div><br>
<span></span></div>
<div><span>I&#39;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><br></span></div><div><span>1. I&#39;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&#39;t tested this.</span></div>

<div><br><span></span></div><div><span>2. I&#39;ve had a go at implementing the filter from <a href="http://www.musicdsp.org/archive.php?classid=3#25" target="_blank">http://www.musicdsp.org/archive.php?classid=3#25</a> 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&#39;t tried this on the iPhone yet).</span></div><div><br><span></span></div><div>

<span>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&#39;m sure those of you with higher math skills will intuitively know why, but I&#39;m just learning calculus now (my early education was a bit chaotic). I&#39;m also limited by the fact that this is for a commercial project (although I&#39;ll be happy to share the code :) so I can&#39;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><a href="http://sharktracks.co.uk/" target="_blank">http://sharktracks.co.uk/</a></div></div></div><br>_______________________________________________<br>


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<br></blockquote></div><br></div>