When you have one or multiple Sound strips you can check `[ ] Draw Waveform` in the Strips `Sound` Properties (on the right, open VSE's Properties Panel with `n`) per Strip.

When you want to set the behaviour for all Strips you can do so since the work on the [gooseberry branch][1]. They introduced this Feature there directly in the VSE's Menu Bar, but later implemented it in the Master Branch into the `View` menu with an own submenu `Waveform Drawing` where you can switch between two global options for turning Waveforms `On` or `Off` for all strips or let each strip determine on it's on property as described above whether or not to display its Waveform via `Use Strip Option`. (You can script this if needed)


[![Example of Waveform Drawing options][2]][2]


  [1]: https://gooseberry.blender.org/gooseberry-tools-the-new-improved-sequencer/
  [2]: https://i.sstatic.net/daVK7.png