An Introduction to Mastering
As mastering engineer ofIgneroid Publishing, many people have asked me about the importance ofmastering. However, in order to thoroughly describe the importance ofmastering, I must first describe some of the equipment and processes availableto a typical mastering engineer.
The equipment used bymastering engineers is very specialized and precise. Most people have dynamiccompressors in their studios but the compressors used in mastering are a bitmore complicated. For instance, the use of compressors that can control high,mid and low frequencies independently. They can attenuate peaks in the audiosignal instantly or even before the peaks occur if the feature a"look-ahead" function. Look-ahead is achieved by sending a directsignal into the level detectors of the compressors and feeding a delayed signalinto the actual signal processor. The compression uses joint stereo operationwhich means that if a peak occurs on one channel of the stereo mix, bothchannels (right and left audio channels) with be attenuated equally. This isimportant because if only one channel is attenuated, there will be a suddenloss in only one channel's volume and thus interfering with the percievedbalance or sound-scape. Joint stereo operation prevents stereo separation fromdeteriorating as compression is increased.
Most people are alsovery familiar with equalizers or EQ. The EQ used in mastering can affect bothright and left channels independently or identically. This is useful if theright and left channels have significantly different frequency content or ifthere is an error in one channel and not the other (if it ainít broke, don'tfix it). Also, the number of "bands" the EQ has can vary, from afour-band analogue EQ all the way to 24,000 band digital FFT filters. FFT meansFast Fourier Transform, which is a method of using delay to control independentbands of frequencies. Why so many bands? Precision, that's why. Some recordingmay have a high pitched ringing going on throughout caused by substandardequipment or from having a computer monitor too close to the recording gear.Normal EQ could eliminate such sounds but would cause severe interference withthe rest of the program material making it sound unnatural. The digital EQ isso precise that it can eliminate the ringing with almost no audible effect onthe program material. It can also be used for split seconds to reduce bum notesor add a little accent to certain instruments without affecting the surroundingmaterial. This is very useful for increasing clarity and overall impact of thesound.
Nonlinear editing toolssuch as a software controlled hard drive system are also important for removingsections of sound for the purpose of making different versions of songs forradio or album cuts, CD singles etc. Fixing bad "punch-in" glitches,and cleaning up fades are also advantages of nonlinear editing tools. The sametools are used to put the songs or other material in the correct order and setthe correct timing between tracks on CDs. These functions also can be performedby "crash editing" between two or more recording deck or even by handsplicing sections of tape. Songs are usually put in the order in which theartist/producer want them as the first step in the mastering stage. Dynamic adjustmentscan also be added with great precision to program material using a nonlinearediting system to increase the impact of the sound. Often, if a song is thesame volume all the way through, such volume adjustments can be added to keepthe material from getting too "boring". The opposite is true also. Ifthe dynamics of some given material varies radically enough that it isintrusive, these can be manually adjusted. This can also be done by hand, thatis, riding the faders on an analogue system. Another real advantage ofmastering is the ability to reduce transients (occasional sudden volume peaks),which prevent the overall volume of the material from being increased. Afterstray transients have been reduced, the signal can typically be boosted 3-9dBlouder than before.
Noise reduction is alsoa very handy tool in mastering. The same basic FFT filter used for EQ can alsobe used to remove AC hum, tape hiss (to a limited extent) or other unwantednoises such as clicks and pops. If there is noise in a particular track like AChum, a segment of the track containing only noise can be sampled in the FFT asa profile for noise reduction. The profile is basically a pattern of sound thattells the computer what "noise" is and thus, an inverse profile isapplied over the entire selection and attenuates the noise. This is incrediblyuseful for restoring older recordings, but any recording suffering from noisemay also benefit from this process.
Mastering engineers alsohave the ability to adjust the stereo field of recordings, even if they wereoriginally recorded in mono. Granted, if you send a mono recording to amastering house, they cannot for instance, pan the guitar to the right and thekeyboard to the left, but they can add stereo space that was not thereoriginally. If the recording is done in stereo but does not have the auralspace it needs, then the stereo field can be accented, creating an improvedsound-scape. There are several methods of doing this that can only be done inthe digital domain, but some methods are done using specialized analogueprocessors. Along these lines is a technique called M-S processing. M-S meansthe left and right channels are remixed as a "Mid channel" and thedifference between the left and right channels which is called the"Side" channel. By utilizing this technique, an engineer canattenuate or exaggerate things in the center of a mix without touching soundsthat are panned out. Compression and EQ can be applied differently to the Midand Side channels. Note this is quite helpful for de-essing vocals. A handytrick is to lower the "side" channel durring softer passages andbringing it back up for louder passages giving an "explosion" ofemersing stereo sound.
One of the lastmastering tricks is time stretching. A song's tempo can be increased ordecreased without affecting the pitch of the song. This is important for makingradio edits of songs, as radio programmers have a tendency to speed up songs inorder to fit more commercials into the day. The tempo of the song can bedecreased so when the radio station speeds it up, it will have the tempo it wasoriginally intended to have. There isn't a large demand for this process, butsome people wanting to make their tunes more danceable or to cheat the radiostations like to have this option. Stretching is also helpful for fixing minorproblems with timing and premature decays in the signal.
One of the most obviousprocesses in mastering are final touches on fades. Often an mixing engineerwill try to fade out a song on their own. That may or may not work well at thetime but after all the mastering processes are complete, the fade will sounddrastically different. Therefore the mastering engineer will have to makeadjustments to the fades as one of the last steps. More experienced mixingengineers will leave the fade ins and fade outs to the mastering engineerall-together because a specialist in mastering can do it with much moreprecision and musicality. Fade-ins and fade-outs need to be clean andconsistent throughout a compiled group of recordings as does the volume levelsof the individual songs. That is, the overall volume of each track is set tomaximize the impact of the whole album. A slower, softer song will sound betterat a lower volume while more up tempo or intense songs will have more impact ifthey are louder. Never-the-less, the volume of each respective track should besimilar so that one flows into the other naturally.
So, the importance ofmastering can be summed up into just a few short statements. Mastering increasesthe impact and clarity of the material. It is the final polishing an album as awhole receives before it is released to the public. Mastering will helpmultiple tracks recorded at different times sound like they "belong"on the same album together.
Who should have theirstuff mastered? Anybody looking for a more professional sound in their workshould have their material mastered. Mastering is a key process in bringingrecordings up to commercial standards. Home-recorded demos all the way toindustrial studio recordings can benefit from mastering. Industrial studioshave their material mastered religiously to gain that extra edge. Manyaudiophiles have their material mastered to compete with the industrial studioswhile musicians with homemade demos may have it done just to increase theimpact of their sound for promotional use. So mastering can serve anybody whois looking for a more professional sound in his or her music. For audiophiles,it is a great help for achieving the perfect sound. For industrial studios, itis a step all to important to skip.
(c)2000, 2004, Stephen J. Baldassarre,
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