They certainly have been talking, just not within the public's hearing range.

For one thing, the sounds are outside the range of human hearing.

Most of their communications were lost to us, being below our hearing range.

This was second only to the bat in range of hearing.

But if the waves are too small, they lie outside the range of human hearing.

The animals had a far better range of hearing and could sound the alarm if it was needed.

I'd sure like to see an analysis of their hearing range.

"They are making sounds far above the range of human hearing," Data whispered.

"If we come within my hearing range of such sounds, I shall recognize them."

This sound is above the range of human hearing.