HPZ1

A two point difference filter UGen. Implements the formula :

out(i) = 0.5 * (in(i) - in(i-1))

Note: the filter's memory is initialized with the first input sample, so for HPZ1.ar(DC.ar(x)) the output will be zero, even at the beginning.

===Examples===

// engage with mouse button
play {
 val sig = PinkNoise.ar
 val flt = HPZ1.ar(sig)
 LinXFade2.ar(sig, flt, MouseButton.kr(-1, 1))
}

// detect changes
play {
 val z  = LFNoise0.ar(2)
 val f  = HPZ1.ar(z)
 val ch = f sig_!= 0 // input increased or decreased
 z.poll(ch, "now")
 0
}