How to implement an SDK that performs real-time manipulation of audio without really knowing how to describe the correct result using TDD? Only when I understa

How to implement an SDK that performs real-time manipulation of audio without really knowing how to describe the correct result using TDD? Only when I understand the problem, the SDK and the expected result I could start writing some tests. TDD seems to be for business applications where you're using tried and tested technology to implement new problems.