[PD] WG: Inverse bandpass filter

Robert Esler robert at urbanstew.org
Wed Apr 23 02:06:21 CEST 2014

Though with DC  you don't have the issue of phase.  I'm not an expert in
filter math, but I assume that by the time your filtered audio (assuming its
not DC) gets subtracted by the [-~] object it is out of phase with the
original signal.  Moreover, I hear a distinct difference.  Maybe I'm not
conceiving your statement properly and perhaps this discussion has been
about DC all alongŠ


From:  Alexandre Torres Porres <porres at gmail.com>
Date:  Tuesday, April 22, 2014 3:51 PM
To:  GCC <robert at urbanstew.org>
Cc:  <apvague at gmail.com>, Ingo <ingo at miamiwave.com>, pd-lista puredata
<pd-list at iem.at>
Subject:  Re: [PD] WG: Inverse bandpass filter

can;t remember where I saw about this, but check this link


see the quote "An easy and practical way to remove the zero-frequency
component from an audio signal is to use a one-pole low-pass filter to
extract it, and then subtract the result from the signal. The resulting
transfer function is one minus the transfer function of the low-pass

doesn't it agree with what I said?


2014-04-22 14:37 GMT-03:00 Robert Esler <robert at urbanstew.org>:
> I could be wrong, but I don't think it's quite the same thing.  I believe the
> signal would be out of phase negating many of the effects of the filter.  I
> would recommend using [biquad~] and in pd-extended there is a [notch] object
> which takes care of the coefficients.  This sounds much cleaner and more
> notch-like to my ear than subtracting the filtered output.
>  There is an explanation in Miller's book if you like unit circle math:
> http://msp.ucsd.edu/techniques/latest/book-html/node144.html
> -----------
> Message: 4
> Date: Tue, 22 Apr 2014 01:59:07 -0300
> From: Alexandre Torres Porres <porres at gmail.com>
> Subject: Re: [PD] WG: Inverse bandpass filter
> To: Ingo <ingo at miamiwave.com>
> Cc: pd-list <pd-list at iem.at>
> Message-ID:
> <CAEAsFmhD0HanLmv9vutcSQZjkZY69i7wMeBqQ+20S2riWYaakw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> isn't it just subtract the audio from the filtered output?
> I guess you can get inverse freq response just by that
> cheers
> 2014-04-18 17:21 GMT-03:00 Ingo <ingo at miamiwave.com>:
>> You could send the original signal in parallel and invert the phase by
>> multiplying with -1. You might have to delay the original signal in case
>> that the processed signal gets also delayed by one or more blocks.
>> Ingo
>> _______________________________________
>>> > Von: pd-list-bounces at iem.at [mailto:pd-list-bounces at iem.at] Im Auftrag
>> von
>>> > AP Vague
>>> > Gesendet: Freitag, 18. April 2014 18:49
>>> > An: pd-list at iem.at
>>> > Betreff: [PD] Inverse bandpass filter
>>> >
>>> > Is there a simple way to make [bp~] or [vcf~] have an inverse function?
>> To
>>> > filter out, rather than pass a changing frequency value. Is the easiest
>>> > way to do this with a combination of [lop~] and [hip~]?
>> _______________________________________________
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