[arm-allstar] notch filter

[Patrick Perdue]

Yes. If there was some way to pipe audio to/from USB devices through 
LADSPA effects, which are easy to implement on Linux, I'd probably use a 
chain consisting of a parametric EQ, a peak limiter, and maybe even a 
very subtle expander.


On 3/28/2022 11:49 AM, "Chris via ARM-allstar" wrote:
> 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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