[PD] dac object question

Mathieu Bouchard matju at sympatico.ca
Fri Jul 9 07:12:20 CEST 2004

On Thu, 8 Jul 2004, Frank Barknecht wrote:

> first: thanks a lot for explaining the DC effects to you and to Lex. I
> did however ask my question slightly ambivalent. I also would be
> interested in why and how a [hip~ 5] filter removes a DC offset.

why: because DC is, in some way, a 0 (zero) Hz wave, and by definition
"High Pass Filter" means something that cuts off low frequencies, which
would include 0.

how: I don't know how [hip~] works, and that is implementation-dependent,
that is, there are many kinds of high-pass filters.

> And related to that: What would be the best way to make sure you get
> no DC offset?

Filter out the DC whereever it is where you don't want it, and don't
filter it where you don't care about it. How you do it exactly is your own

> I normally don't use sound input, so are there other possible sources
> to watch out for in purely algorithmic patches, which might generate a
> DC offset without intention? I see that a phasor introduces a DC
> offset, but should I watch out for less obvious offset sources, maby
> filters and the like?

Depends what you call "without intention"... squaring a signal (e.g.
[expr~ $v1*$v1]) always introduces some DC. It is useful, too. The RMS
volume is defined as the square root of the DC of the square of a signal.

For other filters I don't really know. If you want to probe for DC, you
can do it, using something like [lop~ 1] -> [snapshot~].

Makes sense?

Mathieu Bouchard                       http://artengine.ca/matju

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