Z1202 wrote:Was a bit unhappy with the asymmetric nature of mystran's allpass trick, where one of the bands is obtained by subtracting the other one from the allpass signal.
Why would the asymmetry matter?
Probably it doesn't. Although there is some kind of scientific culture which prefers symmetric things. We have been taught in university to prefer symmetric things whenever possible if there are no reasons for the contrary. Dunno. Often the symmetry can "tell" you something. Things could be easier to analyze, you have additional means of verification. E.g. recently I had to find a maximum of x/(1+x^2) (I don't know it off the top of my head
). By converting it to the symmetric form (x+1/x)^-1 one can immediately see that the maximum is at 1. Of course in this case it doesn't matter much (although it spared me taking the derivative or having to use a CAS), but sometimes you could simply miss something important, which would be otherwise well visible in a symmetric form.
Also the signals are treated "kind of" equally, which means that one would expect similar precision losses and such. Although in the particular case of the hp and lp outputs of "SVF" they are still somewhat asymmetric. But it kind of feels better.
There's actually one more symmetric possibility. Besides the SVF and paraller forms, one could use cascaded form of 2-pole SVFs, using the modal pickup features as I suggested earlier in this thread. Off the top of my head if we used the bandpass signals as the ones fed into the next SVF, the things would be as symmetric as possible.
Edit: so in the end it's just a habit: always look for a symmetric solution. Maybe it won't be found or for whatever reasons won't be taken, but at least look for it and see if it gives any further insights.