New answers tagged audio
You could have a look at how soundcloud allows users to add comments to music tracks. To me it seems quite intuitive and you could draw parallels between it and your problem
When you say signal I am assuming you mean something like a waveform? If that is the case then doing an interface that shows the waveform with sections highlighted that the user can hover over/click on to get more detailed information would be something that makes sense to me as a user.
Top 50 recent answers are included