... I know that when you go the other way — convert lin-phase FIR to a min-phase FIR, — the filter length does not change (i.e. the duration of ringing remains the same).
What is it that you convert, and how do you define "duration of ringing"?
I did a simple MATLAB test, designing some linear phase filter, inverting maximum-phase zeros to have a minimum-phase FIR filter of the same magnitude response. Total impulse response length remains equal, but how do you quantify "duration of ringing" in a way that gives a number <inf for IIR filters? Some "effective" number ala RT60?
When you "render" a filter spec into an actual filter, you loose information about the design objectives. I would assume that designing the final filter directly would come closer to the real goals of some application, rather than design a linear filter, then transform it into some other form?
http://www.dspguru.com/dsp/howtos/how-to-d...ase-fir-filters
N=11;
F = [0 0.4 0.6 1];
A = [1 1 0 0];
b = firpm(N, F, A);
a = 1;
[b,a] = eqtflength(b,a);
[z,p,k] = tf2zp(b,a);
z(abs(z)>1) = 1./z(abs(z)>1);
[b2,a2] = zp2tf(z,p,k);
b2 = b2.*(sum(b)/sum(b2));%normalize DC gain
[H,W] = freqz(b,a,512);
[H2,W2] = freqz(b2,a2,512);
figure(1)
zplane(b)
figure(2)
stem(b)
figure(3)
semilogx(W,20*log10(abs(H)))
axis tight
grid on
figure(4)
zplane(b2)
figure(5)
stem(b2)
figure(6)
semilogx(W,20*log10(abs(H2)))
axis tight
grid on