* What is mastering and why do I need it?
This subject gets really deep, really quick so I'll attempt to explain all this in very broad strokes. If you're interested in studying the subject in more detail, I suggest you scroll to the bottom of this page and check out some of the links.
Simply put, mastering is the process of preparing and organizing your music for mass distribution. Mastering is both an artistic and a technical process so in order to understand it, you need to examine it from both perspectives.
In the big leagues, audio mastering is accomplished in what's called a "mastering studio". Mastering studios are designed, equipped and staffed specifically to handle all the chores associated with mastering audio for wide-spread commercial release. The mastering studio is the bridge between the recording studio where you recorded your project and the duplication company that cranks out the millions of copies of your album that end up on record store shelves.
The typical scenario goes something like this: you go into a recording studio to record songs for your upcoming album. Each song consists of many individual tracks of audio that have to be mixed together. After all the tracking and editing is finished, the songs are mixed down to stereo and then burned onto a CD-R disc. You can play that CD-R disc in any compact disc player and it sounds pretty good (hopefully) but it's not necessarily the thing you'd go to press with. The songs might not be in the correct order or you may have recorded more songs than needed for the final product. The music might sound great in one place and not so great somewhere else. The point is, there's still more work to be done. The next step is the mastering studio. The mastering studio takes the CD-R disc (or it could be a DAT tape or analog reel tape) that you got from the recording studio and runs the audio through special mastering processors to improve the sound quality. Then they determine the track order and the amount of quiet time (if any) between the tracks. Once that's done, they incorporate other elements into the final product such as ISRC and PQ codes, CD text, index marker locations, hidden tracks, etc. Once all that final prep work is done, they burn another CD-R which is referred to as the "pre-master". The pre-master is sent to a duplication company, along with all the album artwork, where the final product is produced.
From an artistic viewpoint, there are usually a number of things that can be done to improve the sound quality of a recording. When I say "improve", what I really mean is that the audio is being modified in order to make sure it translates well in the outside world. People listen to music on all different types of stereo equipment and in many different environments (a car, a home theater, an iPod, a desktop PC, a dance club, a boombox, etc). It's the function of the mastering studio and the mastering engineer to make sure that the final product sounds good everywhere.
In order to accomplish this, mastering studios are equipped with ridiculously expensive, exotic, audiophile-grade playback equipment, in rooms designed from the ground up to reveal all the nuances of a recorded performance. If you've never experienced the thrill of listening to music on a playback system costing $100,000 (or more), in a room which has been finely-tuned for critical listening, then you don't know what you're missing. Sonic details that might have otherwise been clouded or masked are brought to life. The mastering engineer is trained to listen for these sonic details and to make whatever corrections or changes are needed to improve the quality of the audio.
You might be asking yourself, "Aren't recording studios designed for critical listening?". "Why do I need to go somewhere else to make these decisions?". The answer to these questions is two-fold. There are fundamental problems associated with recording studio control rooms, the least of which is all the equipment inside the room. Audio bounces all over a room and anything inside the room is going to have a bearing on reflected and absorbed sound. There is an acoustical problem called "comb filtering" which is a phenomenon that occurs when frequencies travel around a room and interact with themselves. The sound stage can become "smeared" which creates certain problems when you are trying to make mixing decisions. Then there is the concept of having a fresh set of ears involved. Sometimes it's a good idea to have a neutral third-party involved in the decision process. When you're doing all the tracking and mixing you can lose perspective. It's like you can't see the forest for the trees. So there is an advantage to having someone else do the mastering.
The other main artistic consideration to mastering is song selection and track order. A band will sometimes record more songs than they need for the final product. Once you start piecing everything together, you get a clearer picture of how the final product is going to sound. Track order is an important part of the album mastering process. You basically want to get the songs to flow into and out of each other. As with the rest of the process, selecting which song is first, second, third, etc. is a very subjective call. I've seen heated discussions on the subject. The alpha male usually wins out :-) I read an interview in Recording magazine a while back with David Singleton who is the mastering engineer for Robert Fripp and King Crimson. David & Robert would mix an album and put the songs in a particular order. Then they would burn a CD and take it home and listen to it over the course of many days or weeks. As they were listening to the CD, they would note the point where their minds would start to wander off. They would then note that particular song and replace it with something else. This exercise would continue over and over until they could listen to the entire CD without losing attention. So, in effect, each song was in the perfect order to keep their attention focused on the music.
I guess it's worth mentioning that the internet is fast becoming the main method for music distribution. Compact discs sales are plummeting. The album "concept" might be dying with it. These days, MP3 singles are king. The idea that songs are meant to be played in a specific order doesn't hold much weight anymore. So perhaps, the mastering concept will eventually change also. I do a lot of singles mastering which means I deal mostly with just a few songs or songs in no particular order these days. Irregardless of how many songs are involved, my main goal is make sure each individual song competes with other songs on the market. Since the iPod is so popular, you basically want your music stand up to other songs - especially if they are in rotation on an iPod. You don't want your songs to be lower in volume or muddy compared to whatever else might be out there.
The technical process of mastering involves such things as:
* Normalization (or peak limiting). The volume level of most commercially released music these days has been "pumped up" and so you will probably want to make sure your music has also been "pumped up" to commercial standards if you intend to compete with what's already out there. You also want the overall volume level of the album to be consistent from song to song.
* ISRC codes (the International Standard Recording Codes) - this, in effect, is how you ultimately get paid if your music is being publicly broadcast or distributed. Better be DAMN SURE you got this right before you go to press.
* CD text, PQ codes and other embedded mumbo jumbo. Important? Yes. Critical? No.
* Analog-digital conversion. This is very important if your music was mixed down to analog tape (still very common in the big leagues). Quarter-inch reel tape is still used for mixdown. Yes, analog still competes favorably in this digital age we live in.
* Phase cancellation - Mastering studios have been known to kick a mix back to the recording studio from whence it came in order to fix phase cancellation problems (among other things). Phase cancellation is a technical problem that potentially occurs when you record a single sound source with more than one microphone. Sounds might be reaching the microphones at different times and when the two signals are mixed together, they start to cancel each other out. The effect is like you're listening to the sound from inside a tin can - kinda hollow sounding. This can't be fixed in mastering. Has to be corrected during mixdown.
Coffee is running out and your brain is starting to hurt, ain't it?
How do I do it?
The mastering tools that I use are virtual software devices (or plug-ins) which are part of Sonic Core's Scope Fusion Platform software application. You can read more about SFP and the Scope audio platform here.
The main device I use for mastering is called OptiMaster.
OptiMaster is a sophisticated multi-band mastering processor which incorporates a compressor, limiter, expander and normalizer. OptiMaster takes an incoming stereo signal and divides it into three separate frequency bands (hi/mid/low) using an internal 3-way crossover. Varying amounts of compression, limiting or expansion are then applied to each frequency band. The purpose here is to smooth out the rough edges and hopefully create a better balance of frequencies.
Frequently, I also apply a second device called PSY Q which is a type of aural exciter or audio enhancer.
PSY Q makes your recordings sound "better" and "nicer" in many aspects. The processor affects specific frequency ranges in a very methodical manner - and in contrast to conventional equalizers, it does this "intelligently". Thus, instead of merely boosting or cutting a specific frequency range, PSY Q processes the incoming signal via a complex filter structure. With the aid of just a few controls, phase and frequency response are corrected so that the character of the signal most closely matches that which our ears tend to find satisfying. The overall impression is that your mix now has increased presence and transparency.
The equalizer in the PSY Q comprises two units. One unit processes the overall sound, while the other performs additional processing in the high frequency range. The units each have a control which allows you to adjust their effect upon the sound. Bass emphasis can be performed with either a "soft" or "hard" characteristic - that is, either with a smooth and round coloration, or rather crisp and dry. The Mid/High control regulates the effect of the frequency and phase compensation in the rest of the frequency spectrum. The High EQ additionally permits separate control over the critical high frequencies. This is where you can lend your signal the warm, soft and silky character which you're accustomed to hearing in professional productions.
PSY Q incorporates a frequency-selective compressor especially for the bass range. It ensures that signal levels do not get out of hand, even when the bass portion is being heavily processed. The compressor features a reduction meter for graphical display of its instantaneous effect. With the SoftClip unit, you can significantly increase the loudness of your signal and at the same time introduce the popular analog tape saturation effect.
PSY Q provides a continuously adjustable stereo expander (enhancer) which functions independently of the other tools in the PSY Q. It creates the impression that the entire mix is being "pulled apart". Signals which are situated close to one another in the acoustic space become more distinctly separated. Sounds incorporating spatial content gain additional liveliness and presence through the use of the expander.
After the post-production multi-track editing and mixing is completed, I need to play each song through one last time, in order to master it down to a stereo WAV file. Then we then group all the songs together and establish the song order and the amount of quiet space between each song. I use Sony's CD Architect program for this purpose. After all the songs have been properly positioned and the track indexing is complete, the final step is to burn a (pre)master CD-R to Red Book specs. Voila! We're done. Now you can take that (pre)master CD to any duplication service and have thousands of CD's printed up. The (pre)master should be treated with respect. Don't use the (pre)master CD for anything other than making dup's. Put it away in a safe place when you're done.
A few extra comments and observations:
It's generally not a good idea to record, mix and master all in the same day. Ear fatigue is a very real problem. I prefer to give my ears at least 12 - 24 hours to decompress before mixing and mastering a project. It's amazing how different things can sound when you've been away from the project for a while.
I like to spot-check the volume levels of each song so that there isn't a big difference in volume from one song to the next. I find this works best by quickly jumping from song to song and noting the loudness of each song. I want the first song and the last song and everything in between to be more or less the same volume level. I do this work with Sony CD Architect which is the program I use for CD authoring. If there is a noticeable difference in volume for a particular song, I will go back and remaster the quieter song so it's more in line with it's neighbors. You don't want people reaching for their volume controls all the time.
I always tell the client to spend a few days with the final master and listen to it on as many stereos and in as many different environments as possible. If any changes are needed, the client should make detailed notes by track number and return to the studio for another pass. The goal is to get the master to sound good everywhere. If your CD sounds good in one place and bad in another, consider the location and type of equipment being used before you freak out. Some rooms/stereos aren't very musical sounding and you may think you're hearing problems with the mix when, in fact, you're hearing other unrelated problems.
Give yourself a week or two, if possible, to live with the music before you start duplicating. Wait a day or two before doing any critical listening. A fresh perspective always seems to bring out things you missed the first time. I've gone back and listened to mixes/masters I did months or years ago and usually always hear something I think could have been done better. So, the point is, the more time you give yourself for mastering, the better the final product will sound when you go to press.
Alright! Enough already! You're on your own.
Some more information about mastering can be found at:
http://www.colossalmastering.com/
http://www.massivemastering.com/
http://www.theprojectstudiohandbook.com/articles9.htm
http://www.tcelectronic.com/media/bobkatz.pdf
http://www.gatewaymastering.com/