Question

How will you mark something that you can’t hear in the audio file?

Answer 1

unintelligible is the word used to mark something that you cannot hear in the audio file.

Answer 2

There are a number of softwares available these days where one can edit an audio file or mark things in an audio file.

You can search the web for the softwares and select the one that suits you the best. These softwares simplify our work and save a lot of time as well.