CT frequency response

There is nothing about a current transformer that makes it unlike other transformers. The details of the design may vary in order to control distortion and saturation of the core. This design is determined by specifications. Various sources of error have to be controlled by adding extra iron or copper as needed.

That said, measure various parameters as you would an audio transformer to get capacitance, leakage inductances, magnetizing inductgance and other parameters that you would need to calculate the frequency response of an audio transformer.

Bill