The first thing you need to think about when mixing a song is what genre you are working with (see also mixing basics). Each genre has its own characteristics however there are general techniques you can use when to improve your music mix.
Using Delay as a Stereo Widener
One clever trick is to use a delay plug-in to introduce small delays in one or both sides of a stereo signal. in Logic Pro you can create this by selecting the Sample Delay plugin. Set the delay on the right to around 200 samples. Anything higher than 300 samples you start to hear the delays rather than a wider stereo image. This effect, often referred to as the ‘Haas effect.’
EQ and High Pass Filtering
Using EQ for clarity
To create space in the music mix you can EQ to remove problem frequencies. One technique using a parametric EQ to find the frequencies you do not want is to boost using a narrow Q width and go through all the frequencies until you can hear the dissonant/problem frequency clearly. You can then further narrow the Q width and reverse to from a boost into a cut, removing this frequency. Doing this on instruments will free up space in the mix making everything easier to hear and less muddy.
Using EQ to create space
You may have a few instruments that share frequencies. For example: guitar, synths and vocals. You need to think about which instrument you want to stand out the most. In most cases this will be vocals. To make sure that the vocals are not drowned out by these instruments you can cut the guitar and synths at around 300Hz-3kHz.
Leave Space for the Bass
A lot of producers use high pass filters on a instruments other than the bass and kick. This frees up all the rumbles/deep tones that are not needed and leaves room for the low end to be punchy not muddy.
Too Much in your Music Mix
There is always the temptation to go overboard when mixing. For example put reverb on everything, EQ everything. Sometimes less is more! It’s also important to take breaks from mixing as once you have heard a song hundreds of times over you begin to loose interest and stop hearing things like you did at the start.
The brilliant song Billie Jean by Michael Jackson was mixed 91 times by audio engineer Bruce Swedien before it was finalised. The final mix they went with was mix 2. It’s great if you have the time (and patience) to create that many mix versions but sometimes its important to know when to stop and say ‘it’s finished.’