The sound of the rain by Derwent Water

Mrs B made an interesting observation on a very wet Duke of Edinburgh checkpoint by Derwent Water. Out in the open when the rain hits the umbrella, you get a higher frequency sound than when you stand under the trees. I suspect that the drips from the trees are bigger drops, so does that mean that with umbrella fabric you get a deeper note if you hit it harder? I can't believe that this is true for a drum, but further thinking is needed.