Hello chas Tim is right the best way is to get out and listen to the real thing. I was fortunate enough to have be brought up within earshot of Great Bear swamp in NY and couldn't help but to hear them. But if that's not an realistic option, good videos can be found at
www.herters.com. they specialize in waterfowling. One tip for the beginner: if you do hit a sour note, and you, will don't stop on that note continue to call and stop on a good one. I've heard some pretty lousy highballs from the real thing but they don't stop to correct themselves. Good hunting Tom PS. A small repetoire, done well, is better than a large one done in a mediocre