[PD] filter-graph and lop~ phase

[Miller Puckette]

Hi Peter -

I believe the graphs are showing phase delay, which people often graph because
it's positive.  But you're right that the phase response, if measured as
(phase out) - (phase in), is negative.  I think this is probably best fixed
by fixing the example to say that it's showing phase delay, not phase
response, or equivalently, saying it's -arg(H) instead of arg(H)... this is
probably also wrong in the book.  I'd better go look when I have a moment...

thanks
Miller
On Thu, Feb 13, 2014 at 11:35:20PM +0100, Peter P. wrote:
> Hi list,
> 
> just wondering if I am getting something wrong plotting the phase
> response of lop~ using the abstractions filter-graph1.pd and
> filter-graph2.pd as exemplified in 3.audio.examples/H10.measurement.pd
> 
> For a simple one-zero lowpass filter using [rzero~ -1] the phase
> response is plotted going from 0 to pi/2 (eg. 90°) at nyquist
> frequency. 
> I always thought that it would be 0^ to -90° though.
> 
> Also a highpass [rzero~ 1] filter's phase is plotted as
> going from -90° to 0° instead of the 90° to 0° I know from some
> textbooks.
> 
> Is there a mistake I could have had made? I mean, things sound
> alright, but I am just wondering.
> 
> best,
> P
> 
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