APF - Second order all pass filter?

Does anyone knows which filter is the undocumented UGen APF? Second order all pass filter?

Is it this one?

I found this discussion on the list also pointing some bug on it, but I am not sure about it…

@josh you mentioned about writing a help file of it, would it be possible for you to do so?

Hello @fmiramar,

If you like, you can “grow your own” using SOS (SOS | SuperCollider 3.12.2 Help)

BAllPass (BAllPass | SuperCollider 3.12.2 Help) is the 2nd order allpass included in the BEQSuite, which now ships with SuperCollider.

Allpass2 (Allpass2 | SuperCollider 3.12.2 Help) is another implementation, part of the (undocumented) RMEQSuite. You’ll need install sc3-plugins for this one.

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Thanks, I did not remember these ones!