Lots of animals respond to low pitched sounds positively. High pitched feminine sounds are often high stress sounds in the dog world and other animals, alarm noises about predators and territorial sounds are examples. Feeding noises, greeting calls are relatively lower pitch.
So speaking in a very deep voice to animals is the best way to get a positive subdued reaction.
I was rehabilitating a turtle and the only way I could get it to eat originally was playing the lowest key on a harmonica about an inch away from the glass. If you want some armchair scientist explaination as to why that works, well I could go on a wild tangent but it would probably lead back to "Who knows?"
Daedri Elensar
Shipwright to the People
Craig Odell