[arm-allstar] notch filter

[ve3rwj at winsystem.org]

A peak limiter might be useful too.



-----Original Message-----
From: ARM-allstar <arm-allstar-bounces at hamvoip.org> On Behalf Of "Patrick
Perdue via ARM-allstar"
Sent: March 28, 2022 11:41 AM
To: Don Backstrom - AA7AU via ARM-allstar <arm-allstar at hamvoip.org>
Cc: Patrick Perdue <borrisinabox at gmail.com>
Subject: [arm-allstar] notch filter

I have access to a repeater's Allstar node. This repeater has a 162.2 hz PL
tone, and it's rather loud, especially the third harmonic, not so much the
fundamental frequency. Aside from cleaning things up at the source, which is
the best solution, I've tried all sorts of things to minimize that tone.
That frequency is high enough that even using the rather sharp PL filter, it
still leaks through. I've tried various stacks of rxnotch with different
bandwidth, located at the center frequency, and also half an octave to
either side. This gets rid of that harmonic, but it rings out where the
notch center frequency lives. I can adjust how much it resonates by changing
the width or adding more filters. Ultimately, I'd love to use something else
to process the audio, like a parametric EQ rather than a hard notch. A long
time ago, I read about a future iopipe driver for HamVoIP that might allow
for such things to be used. Just wondering what the progress on that is.

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