In the recording process there is probably one thing that has a tendency to be very monotonous. That is the mastering of a song. You will have to listen to the same song over and over again until you finally are satisfied with the mix. Then you listen to a copy of it on your car stereo as you are driving down the road and hear an imperfection or undesirable quality you failed to catch when listening to it on the other 150 occasions you listened to it.
It always seems that just as you think that you are finally finished with the mix down of a certain song; you discover some other fault with the mix and feel the necessity to go back to the drawing board or, more accurately in this case, the mixing board. So it then becomes somewhat apparent that mixing down a song may be a longer process than the actual recording of the song. However, there is something you can do to not only speed up the mix down process but also help you to finish with a better product. That would be the use of frequency slotting.
Frequency slotting is when you assign a specific frequency range to each instrument. You do so to make it easier for one instrument to be distinguished from another. If all of the instruments are on the same frequency range, or slot, the mix will sound somewhat muddy or cluttered. Some tracks may even be completely indistinguishable from others.
So let's say that you have 5 instrument tracks. You have a bass guitar, drums, rhythm guitar, lead guitar and a keyboard track. This is how you can assign a frequency range to each instrument:
The bass guitar can have the bass boosted or use a low pass filter. Makes perfect sense to assign the bass guitar the bass frequencies, doesn't it? That was simple enough. So let's move on to the rhythm guitar. Let's assign the rhythm guitar the mid-range frequencies. Then we can assign the keyboard track the high frequencies. Now we have 3 of the five instruments covered with a minimal potential for them to cut into each others' frequency range. We only have two instruments left; the lead guitar and the drums.
Obviously, the more instruments you have, the harder it is to keep them from cutting into each others' frequencies. But it is still possible to minimize that. We can do that with the lead guitar track by giving it a range somewhere between the rhythm guitar and the keyboard. So it will basically occupy some of the mid-range frequencies and some of the high-end frequencies.
Now we have the drums. The drums can be a bit tricky because you have a number of pieces that are spread across the spectrum. For starters, your bass drum (or bass drums if it's a double-bass) is going to have more bass tone than the other pieces. You may have a number of toms as well that are spread throughout the spectrum. Your floor tom will obviously have more bass than the smaller toms. You also have the snare and the cymbals, with the cymbals being on the high end of the spectrum.
I like to assign the cymbals the obvious high frequencies and add a touch of reverb to add to its sustain. The snare is usually done to taste. It may be mid-range or somewhere between mid and high. The toms are treated individually to spread them out along the spectrum. The bass drum is self-explanatory.
Now you may not have enough available tracks to give each piece of the drum set its own track for the mix down. If that is the case, you should at least divide it into two tracks, whenever possible. I do that a lot of times myself. I will take the drums and give them the mid range slot and the cymbals will be on the high end. It's rather simplistic but it does work well most of the time.
If possible, or if you have enough available tracks, you can assign each piece of the drum set a different area from left to right. That would simulate having an actual drum set being played right in front of you. The bass drum could be in the center, as well as the snare, the floor tom slightly to the left and the crash cymbal slightly to the right while the ride is slightly to the left. You can even try a number of variations of it.
These are some ideas you can kick around. You don't have to use the same exact format I just suggested. I don't even do that myself. The format may be determined by the song itself. It is better to treat each song individually. That will make it easier for one song to be distinguished from another. Also, not every song uses the same instruments or the same number of instruments.
So, in closing: take all of these things into consideration and give frequency slotting a try. You might even impress yourself with the final product. Of course, after you give each track its own special place in the spectrum, you have your overall EQ to tinker with. But that is usually reserved for the fine tuning. Give it a try and good luck.
Photo Credit: "Dudes Rocking Out", created by Bob Craypoe