I use WAVEPAD from NCH.

You should really normalize the wave, and do your compression there as well before you convert to MP3.... remember that the MP3 is already in a compressed format with a lot of missing bits of data compared to the original wave. Just compare the file sizes.... something is missing.

So if at all possible, you want to avoid compressing and normalizing mp3s... not to say that I have not done that very thing because sometimes you gotta do what you gotta do.

It's a really really good idea to do your compression in your mixing software (usually a DAW) because you can alter the mix drastically, throwing the mix off if you apply compression with a heavy hand in an attempt to squeeze every last drop of loudness out of the mix, with a mix that originally has a full dynamic range. A touch to smooth the peaks is OK and likely not too noticeable, but when you start to compress to raise levels and the soft passages are brought to the same level as the loud ones.... you have just throw the mix totally off with a compressor....

And then...after all that to run the NORMALIZE function on it?????

How I do it: I mix in Sonar with a very light compression in the master buss. I do my tracking in such a way, and use envelopes post tracking, so that compression isn't needed to fix it. Just a very light compression on the entire mix. Nothing that kills dynamics and nothing that raises the levels substantially. I export a wave to WAVEPAD and run the NORMALIZE function on it to a nominal level of around -6dB. This level allows for the compression of the bits without causing problems with headroom. I run my mp3 conversion from this point and there is no additional processing done to the MP3. If there are any issues with low volume, I go back to the DAW to make the changes to see what I did differently and fix the levels.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.