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<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>This is a good tech note, but it ignores the input+feedback as a fifth
signal. In fact, using the 5 signals available in the filter, a larger
range of filter modes is possible (at least 31, 22 of which were selected for
the Intellijel Polaris, which uses the 5-input pole mixing scheme). By
disabling the first stage, one gets that input+feedback as the output of stage
1, which means that the disabled modes are limited to 3-pole operation.
There are a significant number of interesting 4-pole modes which require an
enabled first stage.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Also, a public and heartfelt thanks to Rutger Vlek for cluing me in to
adding the feedback to the input for that fifth signal.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>If you want to see the filter modes being utilized on the Polaris,
please consult the Polaris user's manual which is posted on the Intellijel
website:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><a
href="https://intellijel.com/downloads/manuals/polaris_frequency-responses.pdf">https://intellijel.com/downloads/manuals/polaris_frequency-responses.pdf</a><o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>If you're curious, these are the gain formulae for each of the 22
responses shown in that PDF document (Note, every other value is negative):<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>LPA 0 1 0 0 0 HPA 1 1 0 0 0 BPA 0 1 1 0 0 NA 1 3 6 4 0
APA 1 2 0 0 0 <o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>LPB 0 0 1 0 0 HPB 1 2 1 0 0 BPB 0 0 1 1 0 NB 0 1 3 6 4
APB 1 4 4 0 0<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>LPC 0 0 0 1 0 HPC 1 3 3 1 0 BPC 0 0 0 1 1 NC 0 3 6 4 0
APC 1 6 12 8 0<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-right:-11.9pt'><font size=2
face="Courier New"><span style='font-size:10.0pt'>LPD 0 0 0 0 1 HPD 1 4 6
4 1 BPD 0 0 1 2 1 ND 0 4 12 16 8 APD 1 8 24 32 16<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>
BPE 0 1 3 3 1 NE 1 4 12 16 8<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>So, based on this table, there are three modes where the fifth input is
required. These are the ones which require both the input signal and the
output from the fourth stage, so <st1:place w:st="on"><st1:City w:st="on">HPD</st1:City>,
<st1:State w:st="on">NE</st1:State></st1:place>, and APD. The most
important of these is the four-pole highpass mode, HPD. Also, the double
notch, NE, is a very interesting and useful mode that is only available with
the five-input scheme. Finally, the four-pole allpass mode APD is
important for phasing.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Another thing which is cool which was not done in the Polaris, but
which I may do when I finally get around to building a "Doc Sketchy"
version of it, is to crossfade that first input. You will notice that the
first input is always either 0 (off) or 1 (unity gain). It turns out that
one can smoothly morph between various modes by fading this input. For
example:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>NA --> NC<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>ND --> NE<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>LPA --> HPA<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>The most interesting of these is the notch pair ND-NE. When the
input signal is halfway on, the gain formula is {0.5 4 12 16 8}, which is half
of the APD formula {1 8 24 32 16}. This means that when these two notch
responses are input-crossfaded, they go through the 4P AP response at half
gain. I don't know, it might sound cool...?<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Even though they are not listed, there are many other interesting modes
possible when the input+feedback signal is faded in and out against some of the
other modes. One does have to be a little bit careful about total gain,
though. For example, if one does this against the APB mode, one gets the
BPA mode at a gain of 4 when the input is turned off.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>-----Original Message-----<br>
From: Synth-diy [mailto:synth-diy-bounces@synth-diy.org] On Behalf Of Neil
Johnson<br>
Sent: Monday, March 25, 2019 7:59 AM<br>
To: Mike B<br>
Cc: SDIY List<br>
Subject: Re: [sdiy] High pass filter using the 2164</span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Hi Mike,<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> I working on a 4 pole Cascade high pass filter. My present
design uses Lm13700 and works fine, but I would like to switch to the
V2164. I cannot find anyone doing this.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> The issue is the input resistor on the 2164 to convert the voltage
to an input current were as the 13700 is a voltage input. We're would that
input resistor go?<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>> Hopefully this is not a really stupid question.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Olivier Gillet published a nice tech note on making filters with the
SSM2164:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>https://mutable-instruments.net/archive/documents/pole_mixing.pdf<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>That shows how to make a single low-pass filter element, then combine<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>four of them in a chain and from that synthesize a range of filter<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>responses by mixing various tapped outputs together.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Cheers<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Neil<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>-- <o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>http://www.njohnson.co.uk<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>_______________________________________________<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Synth-diy mailing list<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>Synth-diy@synth-diy.org<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=2 face="Courier New"><span style='font-size:
10.0pt'>http://synth-diy.org/mailman/listinfo/synth-diy<o:p></o:p></span></font></p>
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