2pole~ two-pole filter F2p~[2pole~] is a message-based two-pole filter which is less costly than the other two filter objects in MAX: f2p2z~ [2p2z~] and wahwah~. This is the simplest resonant filter possible in Max, the equation being: y[n] = c0*x[n] + c1*y[n-1] + c2*y[n-2] where x[n] is the input signal, y[n] is the output signal and c0, c1, and c2 are the 3 coefficients. See wahwah~ and f2p2z~ [2p2z~].

from the library : ISPW Compatibility Library Format : External Environment : max / msp freeware Max 3.x / 4.x http://forumnet.ircam.fr//rubrique.php3?id_rubrique=65