My advice on calling waterfowl.... it's more important knowing when to not call, than it is knowing when to call.
I enjoy seeing a group of ducks turn into my call, and I enjoy seeing a huge flock of geese turn a half mile away and come straight into my call, and I enjoy seeing someone who is good calling birds. But there's nothing that gets under my skin more than incessant calling.
I've been hunting waterfowl for over 40 years. A lot of crap I hear people calling ducks, I have never heard come out of a ducks mouth. Not the sound, not the cadence, not the timbre. It's gotten ridiculous on public.
Not to disparage a good call or a good caller, but it if I didn't know better, I'd bet a lot of calling is done for the entertainment value.