# [PD] max/pd which is the "right" biquad~ ?

Alexandre Torres Porres porres at gmail.com
Mon Sep 2 07:22:25 CEST 2013

```While in the biquad subject, max to pd translating, I learned that the
order and values of coefficients in both don't match... I checked mmb's
patches and I see they match pd's native biquad~, but both don't agree to
max...

Max does suggest a different order of the coefficients in its help file,
but what we see in practice is yet some other order, and also some reversal
in signs (positive/negative) in a couple of terms.

Just wondering, why the hell is that? Anybody?

Can't deal with formulas really well, but I see they're supposed to be the
same... and I take that from mmb's patches, whose formulas are exactly as
depicted in max (although the help from native pd's biquad~ is somewhat
different, but seemingly equivalent mathematically)

cheers

ps. by the way, here's a patch that converts the order of coefficients from
"max to pd"

#N canvas 150 47 214 262 10;
#X obj 32 7 unpack f f f f f;
#X obj 125 31 * -1;
#X obj 101 55 * -1;
#X obj 41 80 pack f f f f f;
#X msg 41 115 \\$4 \\$5 \\$3 \\$2 \\$1;
#X obj 32 -23 inlet;
#X obj 41 143 outlet;
#X text 69 -24 max;
#X text 87 143 pd;
#X connect 0 0 3 0;
#X connect 0 1 3 1;
#X connect 0 2 3 2;
#X connect 0 3 2 0;
#X connect 0 4 1 0;
#X connect 1 0 3 4;
#X connect 2 0 3 3;
#X connect 3 0 4 0;
#X connect 4 0 6 0;
#X connect 5 0 0 0;
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