[PD] filter-graph and lop~ phase

[Peter P.]

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