79. Why are the CDs that I make quieter than professional CDs?
Most professional CDs used a lot of compression. This can increase the apparent loudness of a song by quite a bit. A compressor reduces the difference between the loud and soft parts of the music. The PG Music Dynamics DirectX plugin has a 'downward compressor' with make-up gain. Downward compressors work by making loud signals softer. After loud passages have been made quieter, you can apply make-up gain to increase the final audio level.
Another thing that you can do is use the PG Peak Limiter on the final output and push it up almost to the red. This will bring up the quieter parts, without allowing the louder parts to distort. Another consideration is that if you have a lot of bass, the music might not seem as loud. Equalization can help with this.
There is a lot of in-depth information available on the internet on the subject of mastering, and you can find many good tutorials by doing a simple search using any internet search engine.