The equipment used by mastering engineers is very specialized and precise. Most people have dynamic compressors in their studios but the compressors used in mastering are a bit more complicated. For instance, I use compression that can control high and low frequencies independently. It can catch peaks in the audio signal instantly or before the peaks even occur. This compression uses joint stereo operation which means that if a peak occurs on one channel of the stereo mix, both channels (right and left audio channels) with be attenuated equally. This is important because if only one channel is attenuated, there will be a sudden loss in one channel's volume which will interfere with the soundscape. Joint stereo operation also prevents stereo separation from deteriorating as compression is increased.

Most people are also very familiar with equalizers or EQ. The EQ used in mastering can affect both right and left channels independently or identically. This is useful if the right and left channels have significantly different frequency content or if there is an error in one channel and not the other (if it ain't broke, don't fix it). Also, I can use EQ from a ten-band analogue EQ all the way to 2,400 band digital FFT filters. FFT means Fast Fourier Transform, which is a method of processing a digital signal using discrete amounts of delay to control independent bands of frequencies Why so many bands? Precision, that's why. I've mastered songs with high pitched ringing going on throughout caused by substandard equipment or from having a computer too close to the recording gear. Normal EQ could eliminate such sounds but would cause severe interference with the rest of the program material making it sound unnatural. The digital EQ is so precise that it can eliminate the ringing without any audible effect on the program material. It can also be used for split seconds to reduce bum notes or add a little accent to certain instruments without affecting the surrounding material. This is very useful for increasing clarity and overall impact of the sound.

Nonlinear editing tools such as a software controlled hard drive system are also important for removing sections of sound for the purpose of making different versions of songs for radio or album cuts, CD singles etc. Fixing bad "punch-in" glitches, and cleaning up fades are also advantages of nonlinear editing tools. The same tools are used to put the songs or other material in the correct order and set the correct timing between tracks on CDs. Dynamics can also be added with great precision to program material using a nonlinear editing system to increase the impact of the sound. One other real advantage of a nonlinear system is the ability to reduce transients (occasional sudden volume peaks), which prevent the overall volume of the material from being increased. After stray transients have been removed, the signal can usually be boosted 3-9dB louder than before.

Noise reduction is also a very handy tool in mastering. The same FFT filter used for EQ can also be used to remove AC hum, tape hiss (to a limited extent) or other unwanted noises such as clicks and pops. If there is noise in a particular track like AC hum, a segment of the track containing only noise can be sampled in the FFT as a profile for noise reduction. This profile is applied over the entire selection and (hopefully) attenuates the noise. This is incredibly useful for restoring older recordings, but many new projects I've worked on have also benefited from this process.

Mastering engineers also have the ability to widen the stereo field of recordings, even if they were originally recorded in mono. Granted, if you send a mono recording to a mastering house, they cannot, for instance, pan the guitar to the right and the keyboard to the left, but they can add stereo space that was not there originally. If the recording is done in stereo but just does not have the aural space it needs, then the stereo field can be accented, creating an improved soundscape. There are several methods of doing this that can only be done in the digital domain, but some methods are done using specialized analogue processors.

One of the last mastering tricks I should mention is time stretching. A song's tempo can be increased or decreased without affecting the pitch of the song. This is important for making radio edits of songs, as radio programmers have a tendency to speed up songs in order to fit more commercials into the day. The tempo of the song can be decreased so when the radio station speeds it up, it will have the tempo it was originally intended to have. There isn't a large demand for this process, but some people wanting to make their tunes more danceable or to cheat the radio stations like to have this option.

So when people ask me what the importance of mastering is, I could sum it up into just a few short statements. Mastering increases the impact and clarity of the material. It is the final polishing an album as a whole receives before it is released to the public. Final touches on fades, song order and volume are all made here as well as some correctional touch-ups.

Who should have their stuff mastered? Anybody looking for a more professional sound in their work should have their material mastered. Mastering is a key process in bringing recordings up to commercial standards. Home-recorded demos all the way to industrial studio recordings can benefit from mastering, which is why I stress the importance of it so much. Industrial studios have their material mastered religiously to gain that extra edge. Many audiophiles have their material mastered to compete with the industrial studios, and musicians with homemade demos may have it done just to increase the impact of their sound for promotional use. So mastering can serve anybody who is looking for a more professional sound in their music. For audiophiles, it is a great help for achieving the perfect sound. For industrial studios, it is a step all to important to skip.

(c) 2000, Stephen J. Baldassarre,
All rights reserved.
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