Audio silence on 1.0
For transmission of audio by amplitude modulation of for example light, the audio can be made unipolar in order to make silence correspond to no transmission which for some receivers means no noise during silence. Just a guess but your audio may have gone through such processing. From the look of the waveform it may have worked like this:

Start with bias = 0. For each time step:


bias = bias + constant, where constant determines the slope seen during silent segments in your graph
If bias + input &gt; 1, then set bias = 1 - input to avoid clipping.


It is not possible to exactly recover the original audio from the output of such processing, but you could use a similar method that keeps shifting the bias towards the direction that centers the audio, and changes the bias appropriately any time the audio would be clipped.