The display of waveforms (or, more correctly, peak envelopes, since the actual waveform is only visible at the highest zoom levels) is configurable via the Edit > Preferences > Editor dialog, to support different usecases and user preferences. The following options are available:

Show waveforms in regions

By default, Ardour draws waveforms within audio regions. Disable this option to hide them.

Waveform scale

Linear

This is the traditional linear (1:1) display of the peak envelope, or, at higher zoom levels, the individual samples.

Logarithmic

Alternatively, you can use a logarithmic display of the peak envelope. This will give you a better idea of program loudness (it is similar to dBs) and plot soft passages more clearly, which is useful for soft recordings or small track height.

Waveform shape

Traditional

The zero line appears in the middle of the display and waveforms appear as positive and negative peaks above and below.

Rectified

The zero line appears at the bottom of the display and waveforms appear as absolute peaks above the line only.