Have you ever noticed that songs played on the radio sound more powerful than when you play them from a CD (on the same sound system)? Are your own songs sound less powerful than professionally mixed songs? Why are ads on TV much louder than the actual programs? (at least on Swedish TV). The answer is compression.
A compressor (or it’s cousin the limiter) reduces the dynamic range of a signal, the difference between the loud parts and the quiet parts. If you compress a song and raise it’s new peaks to the maximum volume it had before compression, you will get a much louder sounding result even though the maximum volume is no different, a subjective feeling of “more power”.
Compression is usually done during the mastering stage of recording, after all the mixing is done. There is nothing that says mastering has to reduce the dynamic range, it could just as well increase it – depending on the intended distribution medium for the song. However, in recent years more and more compression has been applied. And usually radio and TV stations apply even more compression when broadcasting the song. Audiophiles shudder at this, why ruin the dynamic range and compress so hard that signals are even lost in the process? (known as clipping). Some bands are especially known for this, giving rise to mock videos such as this one (which is actually a really good instruction video on how mastering can go wrong):
After all this you might think compressing is just bad, but fact is that correctly applied it will make your songs sound more powerful and more “professional”. And there are free tools that can help you with mastering. Anyone who has done professional mastering will laugh at the thought of automatic mastering, but for us DIY:ers an automatic compressor that squeeze the hell out of your song while assuring there’s no clipping is actually a pretty handy thing.
TLSMaximizer is made by Swede Daniel Lind, aka TbT. It hasn’t been updated in years and it’s not really pretty, but it’s hailed on almost every music forum as the best automatic limiter. Just apply it to your master track and set the EQ to something you like (it even has an option to “add more body”). And it’s free! The license says not for commercial use, but Daniel has later explained this means you are free to use it on commercial tracks but no make money off of the plugin itself (by reselling it).