Matching audio levels

What is the best way to match audio levels? On the two graphs below I want to match based on the light blue levels in the center, bringing the song on the left up to the level of the song on the right. The attempt here is to bring the voices in the two songs to the same audible level so as to no have to keep adjusting volume controls.

You can’t look at the waveforms and tell instantly how loud things are going to be. Worse, if everything is pretty loud to begin with, any adjustment may create damage and distortion.

However, Chris’s Compressor was designed to do exactly what you want. He designed it so he didn’t have to constantly adjust the volume of his music in the car.