When creating magic, I usually draw from the physical laws that govern and maintain our world. Things like the electromagnetic force or gravity, for example. The small number of applications I've listed for Claw's sound abilities are actually rooted n the domain of reality. Try Googling some of them if you're interested. 

I've yet to decide exactly what Claw can and cannot do with his powers, but I'm probably going to tie them in with his deeds, accomplishments and childhood. He learned most of what he knows from his mother, who unfortunately grew to hate Claw for something that he did. In the early years, he was probably schooled in the non-violent uses of Echoing, while Claw himself learned much in its offensive capabilities when he and his mother began feuding with one another.