Final Mix Down
The final mix down entails sending all of your work to a simple stereo pair of left and right signals. All the levels and effects need to be taken care of in advance. Whatever you commit to, the final file is it! If you're working with automation, get that in order too. At this point, you should feel comfortable that you have a good product. Remember the fade-out at the end if you want that effect.
Where do I start if I have sixteen or more tracks to mix?
The drums are usually mixed first, starting with the kick drum. Bass is added next. Vocals are usually last. Compression is added on a track-per-track basis on the instruments that need it, and effects are added to auxiliary channels. Once the engineer has a rough mix, she starts tweaking EQ, setting all the effects levels perfectly and starting to craft the mix.
Bounce to Disk
On digital systems, most notably computer systems, the process of a final mix down is achieved by “bouncing” to the disk. All the audio is bounced together onto the hard drive into a file (usually a stereo file) that can be burned. Bounce to disk is the same as mixing down to a tape or any other format. On many computer systems, bounce to disk is not something you control. This means that you can't play with levels and ride faders while it's bouncing. Many programs just do it quickly while you wait. The reason they do this is that all of the software available lets you automate movements of faders and other parameters. If you can automate, then you should. Once you have the final file, you can burn it to a CD using your favorite CD burning software, like iTunes.
The standard for encoding digital information onto a CD is 16bit/44.1kHz audio. Every CD available today plays back that way. The newer computer audio systems advertise better-than-CD quality, and if you're getting into computer recording you might be able to record at that quality. Nowadays, most computer audio systems record at 24bit/96kHz or higher.
Without getting too technical, the higher the numbers, the better quality you get. The problem is that if you record at 24bit/96kHz, you can't just burn that to a CD, because it's not compatible with current CD quality, which is called red book standard. You have to do something called “down sampling,” which means mixing down to 16bit/44.1kHz. In your software program, this is easy to do. In the bounce-to-disk window, you'll always be asked what rate to mix down to. If you are making a CD, you always need to mix to 16bit/44.1kHz.
How long does it take to mix a song?
Well, how long do you have? Mixing takes a very long time; you will most likely listen to the entire song twenty to fifty times before you get close to finishing. Now you know why bands take so long to release albums.
Okay, so now to dither. When you “down sample,” you lose some of the audio quality because the computer goes from a higher sample rate to a lower one. Dithering was invented to make up for the loss in quality. If you're recording at better-than-CD quality, you need to dither your music down. On many systems, dithering is a plug-in you put on the master fader. On some systems, it's a box you can check in the bounce-to-disk window. Either way, if you record at anything above 16bit/44.1kHz, you must dither it. If you don't, you can hear the difference. Your recording will sound better with dithering.
Now that you have your mix in your hands, you need to start playing it on as many systems as possible. Play it in your car, on your stereo, on your mom's stereo … you get the picture. Play it everywhere you can. The goal here is to make sure that it sounds the way you want it to sound on every system. Certain mixes sound great at home and quite bad in the car. Most professional recordings sound good on almost every system they're played on. If you find some problems, you can always go back and remix. It's also good to play the song for as many different people as you can, especially musicians. Opinions at this stage in your development are very worthwhile.