Ser Waymar met it with steel. When the blades met, there was no ring of metal on metal; only a high, thin sound at the edge of hearing, like an animal screaming in pain. 'at the edge of hearing', how should i understand that?
The edges of hearing are 20 hz and 20 khz depending on your age and love of loud music. 20 khz is metaphorically known as the high edge of hearing. Children's voices are "high". Men's voices are "low". Why? Who knows. It's just a metaphor. I could get into wave length but this isn't physics.stackexchange.
The line is saying that the clashing blades sound more like tiny tuning forks rather than big tuning forks. Smack some paper clips together and it might sound the same.