Spectrogram time scale label is backwards #434

I just realized that the X-axis time scale labeling on the spectrogram is backwards. Time "zero" for the actual drawing is on the right, as that is where the "current" time is when the spectrogram is rendering. As the graphic moves leftwards, the time "since drawing" increases. The X-axis is labeled in the opposite direction, showing time "zero" on the left, with the total length on the right.