What tool is primarily used to adjust volume levels on a track in Pro Tools?

The volume fader is the primary tool used to adjust volume levels on a track in Pro Tools. It provides a visual representation of the volume level, allowing for precise adjustments. By manipulating the fader, users can increase or decrease the audio level of individual tracks within the mix. This is essential for achieving a balanced mix where all elements of a project are at the desired audible levels.

While instrument tracks are used to record and play back MIDI information, they do not directly adjust audio volume levels. The track compressor serves a different purpose, as it dynamically controls the audio signal's dynamics rather than simply adjusting volume. Lastly, a signal path refers to the route that audio signals take through the software but does not serve as a tool for adjusting volume levels. Thus, the volume fader stands out as the direct and intuitive way to manage volume levels in Pro Tools.