Re: _SMA3: A steep roll-off lowpass filter

[DH <catapult@xxxxxxxxxxxxxxxxxx>]

The time domain response actually looks similar to a Cauer elliptical
filter, the way it rolls off steeply and then goes fairly flat with some
ripple in the stopband. I've never tried coding a Cauer in TS but I've
seen them used in speaker crossovers. Conceptually, it would be a 4-pole
IIR filter with a notch filter about an octave above Fc. In a passive
crossover, it's just one extra cap in parallel with the second coil to
create the notch. Done right, it rolls off like an 8-pole filter for the
first 40dB or so and then flattens out without too much ripple. The DC
group delay is about like a standard 4-pole.

-- 
  Dennis

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