Mix to what sounds good!
I agree with most of the stuff said in this thread. Inversely, I disagree with much of it in some situations. Sigh.......audio production.....
Getting your mixes as close as possible to the finale sound you want is the most desirable thing you can do. If you can make the mix happen, then that is less for the mastering process to take care of. In effect, the process of mastering pastes a much different sound on the audio then what you can do at mix time. Mastering is about subtlety, not gross fixing!!!
Mastering can be a lot of different things. It can be just arranging the order of songs and applying a slight amount of tonal and/or volume change (same difference really...). Any cut of boost in eq that exceeds around 2db means that the mix had some problems. Any volume change that is more the maybe 3db also means the mix had problems.
I will not go on and on about this. All's that I can say is that you should have your mix as close to possible to the volume and eq you want BEFORE mastering. Mastering is just supposed to add a slight "polish" to the sound. Correct a few discrepencies from song to song. That is all.
Mastering CAN be about really changing what is there too. But this is not without both good and bad results to the original audio. If the mixes are way too quiet and/or the tonality of the mix is off then mastering can certainly correct these things, IF, the engineer understands what he is doing, and what the benefits/drawbacks are. Hopefully, in mixes that need major changes, the benefits outweight the drawbacks. But the skill of the mastering engineer has a lot to do with this.
Don't forget that mastering is every bit as much of a creative contribution to the finale product as songwriting, performing, tracking, and mixing. What the mastering engineer does or does not do to the audio is subjective, and can add benefits and/or drawbacks to the finale product.
Bottom line. Make your mixes as close to what you want. Let mastering take them to the next level. If your mixing skills are weak, you will rely upon the mastering process to take the product to a much higher level. If your mixing skills are good to excellent, the mastering process will just give it a slight nudge to the better (hopefully).
I read an interview with Bob Ludwig, possibly the most well known and respected mastering engineer ever! In it, he said that much of the material he gets in from the big time studios requires nothing more then a 1db volume adjustment from song to song, and in rare cases, a slight eq tweek. Of course he is quite prepared, and quite possibly one of the most skilled people to deal with any drastic changes that may need to take place, but, simply put, he will not touch the audio with any processing if it doesn't need it.
That is not only a testiment to his skill, but also to the skill of the engineers that have mixes submitted to him for mastering. The point is that the mixes sound outstanding without any further processing needing to be done. Anything you do in mastering could possibly be good or bad to that. Sometimes it is just best to leave it alone, even if that means letting a little tweek that you could have done go.
The hottest possibly signal is not always the best sound for the material in question. To illustrate:
Compare Tracy Chapmans Fast Car CD to Everclears first release. You will find that the Tracy Chapman disk hardly ever reaches digital 0. Everclears first release resides in the -4 to 0db range through out the whole CD!!! We are talking about at least a 6db difference in average level between these two CD, more then that in many cases!!! But you know what? Few would argue that the Tracy Chapman CD just flat out sounds way better!!! It has sweeter sounds, and is far easier to listen to throughout. The Everclear CD tires my ears after 2 songs. It is fatiquing to listen to.
So which is better? The CD that is lower in volume, but very listenable? Or the CD that is maxed out in volume, and makes me want to turn it off after 2 songs?
Which way would you want your CD to sound?
Do you want people to get tired of listening to your CD for some inexplainable reason, or do you want them to play it over and over again?
Loud is not always good. People are so hung up with trying to get their home recorded project to sound as loud as big time modern products that were produced in the finest facilities in the world, with the premier engineers in the world. Thing is, these products don't always sound all that great really. Sure, they are clear, and they definately are very loud. But many modern recordings are very annoying to listen to after a couple of songs. Whereas, older recordings that are much quieter are far more enjoyable to listen to, and you find yourself listening to them over and over again. It is not just a difference in the songs, it is how the audio was dealt with. Older recordins just seem to have more dynamics and color. Most modern recordings seem to have very narrow dynamic and tonal characterists.
Mix and master your CD to sound good, not to compete in volume with other products. You may be trying to compete with a product that could have sounded much better at a lower volume. Yes, you can jump on that bandwagon and blast the shit out of it, but that may not do a thing for making your music more enjoyable to the average listener.
I will end here. Either you get this or you don't. If you don't, then you will keep asking how to make your product louder.
If good sound is what you are after, forget levels and just do what sounds good.
Good luck.
Ed