Gain Envelopes
In Ardour, every audio region has a gain envelope. It is a form of automated gain change that is embedded in the region. The gain envelope remains associated with the region when it is moved or copied.
Region Gain envelope is only visible in the Draw and Edit modes. Clicking on the Draw tool will cause all the gain envelopes on all regions to show themselves. These will appear as lines with square dots (control points) at the beginning and end of each region. The vertical axis represents gain, with the top of the region representing +6dB and the bottom representing -inf dB (silence). By default, the line starts and ends at 0dB; the control points can be moved up and down to change the amount of gain at that point.
Gain follows the line between control points continuously and accurately during playback, and adjusts the gain for that region accordingly. Unlike fader gain automation, region-gain is not smoothed to prevent zipper-noise or amplitude modulation.
Manipulating Gain Envelopes
The default envelope is neutral (0dB) and disabled (gray line). Changing the gain by dragging any of the two existing points or adding new points in draw mode automatically enables the envelope. Clicking anywhere in the region where there are no existing control points adds a control point to the envelope; it will appear on the line at the X-axis of the mouse's current position in the region.
Region gain envelope can be disabed for selected regions via Region > Gain > Envelope Active.
Once added, a control point can be Left clicked and dragged to the desired location. Hovering over a control point will show its current level in dB. Left clicking a control point and pressing Delete, or Right clicking a control point deletes it.