Tests are redundant

[artpelling]

I think a lot of the tests (at least regarding the _Audio related classes) could be simplified by using mark.parametrize with different input signals. A lot of tests are identical across test_audio_signal.py, test_audio_time_data.py and test_audio_frequency_data.py. I suspect that one can find more of these instances.

[mberz]

I think a lot of this was implemented before we discovered parametrisation is a thing :)