You can try NORMALIZE; it should equalize the volume so that all clips are at about the same volume level. However, unless it has been changed since PD11, this feature doesn't work in the same manner as most normalize utilities. They set overall volume (aka gain) to the maximum usable level before distortion occurs.

In order to manipulate your tiimeline in an external audio editor, PRODUCE the audio to a WAV file, (click on the musical note button). Then open the WAV file with the audio editor, adjust gain and make other enhancements as desired. Import the result back to PD and substitute it for the original track, making certain that it's positioned precisely the same.

Normalize in an external editor won't make all clips the same volume, if there are several of varying levels. That's not its function. Independent adjustment would be required. Here's a widely used, capable FREE audio editor: http://audacity.sourceforge.net/