polyphase allpass filters for oversampling

well, that

(6 Votes)
kamedin
1.1 (Updated 4 months ago)
3.5MB
March 25, 2021
Reaktor 6

DESCRIPTION

Elliptic half-band filters implemented with allpasses, for up/downsampling. They have very low passband ripple, high attenuation and a short transition band. They are relatively light on the cpu. The cost -some variable group delay.

The resampling is done in 2x stages. A 1-input, 2-output macro does 2x upsampling; connecting it to a 2-input, 4-output one does 4x, and so on. The fractions of sample rate (SR/3, /4, etc.) are the corner frequencies of the filters. The passband remains almost flat up to that point, then falls to -3 dB at SR/2, and keeps falling.

v1.1: added a more relaxed, faster set of macros (SR/3) for general use, kept the old one (3/7 SR) in a separate group, reorganized. Notes and tests revised.

COMMENTS  (6)

andrew aronson
3 months ago
oooohh. yeah, the thing is we like to say 'standard' to avoid triggering laureano. you gotta understand, because its not his fault, but he really, really hates the monarchy
Justin Luchter
3 months ago
What is -3dB in Imperial?
kamedin
3 months ago
*insert anything but the metric system meme* lol! I updated the description clarifying that. Hope people don't run away now (?)
andrew aronson
3 months ago
this macros for oversampling have fractions in them. maybe they are something great, but over here in the states we don't use the metric system, and i am but a simple farmer. so if you think i won't avoid using these for no other reason than a vague unease i cannot name that comes down to nothing more than a fear of fractions and being too afraid to ask whether an 8x macro labeled SR/8 would just cancel out to regular, then i don't know if i can in good conscience say that this offering, while fantastic, is really very considerate. hm. to be fully honest though i do think oversampling macros labeled in fractions of the sample rate could be unclear to a lot of people, and while i think i have worked out that it only refers to the corner frequency from the documentation, i still wouldn't get in front of a crowd and stake my life on it, so including a section to make that totally unambiguous to anyone who bothered to look would really give this upload that patina of Q factor, imo
Paule
4 months ago
Thank you, Laureano.
andrew aronson
4 months ago
neat. only stopping through the U: to find a limiter because i just put an allpass in a ladder filters feedback and am scared to proceed without one. this post makes a nice 2 for 1
now