[sdiy] Removing the effect of a DC blocking filter through DSP

Didrik Madheden nitro2k01 at gmail.com
Sun Dec 11 16:31:59 CET 2022

Thanks. But this is not audio from a microphone at all. It's audio
generated from an 8-bit game console, which I need to analyze for hardware
research about quirks in its audio generation circuit. Hence why I alluded
that I can easily generate a step function for reference. Ie, I'd write a
program for the console that changes a DC offset.

On Sun, 11 Dec 2022, 16:18 Mike Bryant, <mbryant at futurehorizons.com> wrote:

> This tends to imply you have an A-D convertor in the chain.  This will
> affect the step impulse you want to use for calibration possibly more than
> the capacitors.  You will also need to roll off your correction filter
> before you get to DC - there's a lot of crap around at <10Hz which if this
> is music/voice you won't want.
> Conversely if it's geological audio or something like that, I'd suggest a
> different mic system that is dc coupled :-)
> ------------------------------
> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Didrik
> Madheden via Synth-diy <synth-diy at synth-diy.org>
> *Sent:* 11 December 2022 14:49
> *To:* SDIY List <synth-diy at synth-diy.org>
> *Subject:* [sdiy] Removing the effect of a DC blocking filter through DSP
> Today the thing I'm tasked with is that I have some audio recorded
> through a setup containing one or more DC blocking caps, and would
> like to recover the unaffected audio. In principle, this could
> potentially be fairly simple depending on the circuit: model a 1 pole
> HP filter and run it backwards. Of course, the issue is that you would
> be integrating over a fairly long period of time (in my case I'd need
> to do it over multiple seconds) and the output is likely to diverge
> easily. I'm able to produce a step function from this system as a
> reference.
> Before I roll up my sleeves and try to code something myself, is there
> any project or code examples that does exactly this, in particular
> automating or visualizing the trimming of the parameters needed to
> avoid divergence? In the ideal case, such a software might have a
> waveform view where I can select part of the reference waveform that's
> silent, for extracting a corrective DC offset, and the pulse of my
> reference step function, for extracting the filter parameters, and out
> comes the parameters I need.
> --
> /Didrik
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