One of the biggest problems I faced during mixing this particular project was figuring out what my approach to compression would be. Believe me when I say, compression can either make or break your mix. While some tracks needed a lot of compression, others not at all.
For all you newbies, Compression or dynamic range compression is the process of narrowing down the range of dynamic volume of a track. In other words, when you apply compression to a track, the louder parts of the track might get lower in volume and the softer parts, louder. In common man terms, compression tries to level out the audio range of your track. It is a very important technique used in mixing music extensively. Enough with the producer talk, time to talk about something else.
One of the most difficult and processed tracks on a song are usually the drums, especially if it's more of a rock track than an electronic arrangement. However, compression has to be used sparingly and not to be slapped on everything, something a lot of producers tend to do these days. Sometimes you have to look at the odds and see if everything manages to balance itself out in a mix. Other techniques like EQ, automation and various types of aural exciters can always help to take your mix where it needs to go.
There are a lot of sample libraries and instruments like violins and cellos that sometimes end up taking a large chunk of the 5-10k spectrum of the frequency range in a track and that's somewhere the lower end of the vocals might end up sometimes. At the end of the day, if you can't hear it in a mix, it's probably not worth it to keep it around. There is of course the Fletcher-Munson curve that you have to learn to deal with. You can read more about it here. To put it in short, we all have a hearing bias and nobody has a perfectly flat perception of hearing.
More exciting times ahead, Ciao.