How to match audio levels across tracks?

Question

I'm creating a CD of two-person conversations to use for language study--30 conversations in all. There are several different voice sources; all of them were recorded in a studio, though at different times and places, with small variations in audio levels.
For each conversation, I start by putting each voice in its own track in the timeline. Then I go into the mixer to balance them. While playing the tracks, I check to make sure that the overall volume is just short of maxing out in the Out 1 channel strip; if the red peak indicator comes on, then I lower the volume slightly in the offending track. Once everything is OK, I go back into the timeline and use Export Mix to save the conversation. I go through this same procedure for each of the 30 conversations.
I thought this would result in 30 tracks which have the same overall volume; however, when I burn these tracks to a CD and play them one after another, there is enough variation between tracks that I am forced to fiddle with the volume on the CD player.
What's more, some of the tracks are a bit softer than I'd like. I want to be able to play the CD in a classroom and be sure that all students can hear it clearly. Yet, while I was mixing each track, I made sure to run the volume up as far as possible without causing clipping.
So my question: Have I done something wrong? Is another step needed to get separate tracks to match levels? If so, is this done within Soundtrack, or is it done when burning to CD? And how does one get the tracks even louder without causing clipping?
I'm quite new to audio work, so any help would be greatly appreciated!
Dual 1 GHz Quicksilver   Mac OS X (10.4)  

Answer 1

I just did a similar project, and I must agree that compression is your friend! It's also an art form. I recommend you search the web and find an introduction to the concept.
You can think of it like this: You set a "threshold", and the compressor automatically reduces the volume of any part of the track gets louder than your threshold. This can have the effect of making the quiet parts of your track louder without letting the loud parts clip.
Of course, there are trade-offs. Go too far, and you'll squash out all the dynamic range from your audio. Also, making the quiet parts louder means making the noise louder too!
Play with it and see if it helps: Click on the "*" button on the track, and add the Soundtrack Pro Compressor effect. Click the "Advanced..." button for the effect, and click the "Show Presets" button. Under "User Presets, Vocal Compressors" you'll find some good starting points. Try them all and see what kind of effects you get.
Once your tracks are balanced you can experiment with putting a single compressor on "Out 1". It can help you get the level of your whole mix up without inducing a bunch of clipping.
Yo should also experiment with the "DeEsser" which helps take the edge of "sss" sounds, among other things. It might be very useful for your project. Take a look at the presets and listen to what they all do. If you use both DeEsser and Compressor, you should probably put the DeEsser first.
When you play with effects, it's good to strive for moderation and to give your ears a break once in a while. Also a good idea to listen to your results on multiple speakers. It's easy to get carried away and make your audio sound very unnatural!
Have fun!