Mastering Part 1: What is Audio Mastering?
This is the first of a four part piece on audio mastering. Since I tend to wander and often get sidetracked, the discussion will likely also touch on music production and mixing, and the music business in general. In Part 1, we will examine the definition of audio mastering; what it is and what it isn’t and briefly describe the process.
You might call mastering the icing on the cake. In some ways it is.
Audio mastering started back in the days of vinyl records. Once a song was recorded in the recording studio, it would be sent out for mastering. This included preparing the song so it could be cut with a record-cutting machine which would spin a lacquer disk and use a stylus or needle on a cutting head to imprint a spiral grove which contained the audio information converted to mechanical format. This disc was then coated with silver or nickel to make a negative from which to mold a metal version of the disc called a “mother.” The mother was then used to make stamps (negatives of the mother) for both sides of the record. These stamps were put in a hydraulic press with steam heated polyvinyl chloride (vinyl) injected between them which was pressed into the shape of the final record.
There were limitations on how much music a record could hold because the longer the duration of the music, the closer the grooves in the vinyl had to be. If they were cut too close together, they could cut into each other. An “LP” could hold about 25 minutes of music per side. There were also limitations on the dynamic range because if the music got too hot, the stylus or needle on the cutting head could bounce right off of the lacquer and they would have to start all over. The person who did the cutting had to control the levels to make sure they didn’t get too high. This was the start of audio mastering as we know it.
As the process evolved, these mastering engineers as they became called, started to use more and more processing equipment to control and shape the music they were cutting. They discovered that they could make records sound better. They started using equalizers and compressors. In the height of the pop record era, from 1950s to the 1980s, good mastering engineers were in high demand.
With the conversion to cassettes, then CDs and now MP3s and other digital formats, the cutting of vinyl is no longer part of a mastering engineer’s normal job (though vinyl has made somewhat of a comeback for some genres like dance/club music). But the task of making the music sound better through EQ and compression has not changed. So let’s try to define audio mastering and briefly outline the process as it is done today.
Mastering is not mixing, though they are related and use a lot of the same tools. Mixing is the process of choosing what sounds, instruments and vocals will be included in song, how loud each of these components will be, how they will be positioned in the stereo image (panning), how they will be EQ’d and what effects will be applied. I can remember in the old days, every available hand would be needed to turn knobs and adjust faders in the mixing process. The engineer, tape-op, producer and sometime the whole band would be at the console; a pretzel of bodies, arms, hands and fingers. Fortunately, we have automation now and can program all of these changes to happen exactly the same way every time we play the song back. At the mixing stage, all of the song’s components are still available individually. Nothing has been set in stone. If a vocal is a little buried in one spot, we can just turn it up or adjust the EQ, or use a plugin like Waves Vocal Rider. Once a song is mixed, it is formatted as a single stereo wave file. You can no longer EQ or put an effect on one part without in some way affecting the entire mix. Everything is pretty much locked in. Major changes are no longer possible.
So the mastering engineer gets the complete song, mixed as a stereo wave file. He can’t go in and make changes to individual tracks anymore. He can’t turn down the reverb on the lead vocal or fix an out-of-tune guitar part or tweak that fill where the drummer got sloppy and didn’t quite get the beat right. Those are all things that should have been fixed in the tracking or mixing stage. So what can and does a mastering engineer do then?
Unlike a recording studio control room, a mastering engineer listens to music in a room that is designed and treated to give as flat a frequency response as possible and not color the sound. They have really good monitors and the room is laid out for critical listening. Using a computer with many audio plugins and often a collection of vintage hardware processors as well, the mastering engineer uses mainly his ears with the help of voltage, frequency and spectrum analyzers and critically examines your music. Are there any frequencies that are annoying or muddying the sound? He will go in and use EQ and filters to cut them back. Could the snare use more punch? He might added some compression and EQ at 150 Hz. Are there certain bass notes that jump out? Maybe cutting the first harmonic at 440 Hz will tone down that resonant A note. Would the vocal sound better if it was a little brighter? Maybe add a few Db notch at 2.4 kHz and a shelf at 10kHz. The mastering engineer fixes and enhances the mix. He also added compression to different frequency ranges using a multi-band compressor or sometimes several compressors. He might add a bit of harmonic distortion or a touch mastering reverb. He will adjust the stereo image by widening or narrowing it at different frequencies. And yes, he will use limiters to make your music much louder. Though the more he compresses and limits it, the narrower the dynamic range becomes. There is a lot of debate right now on whether or not we have gone too far in the loudness war. I personally would rather my music sound a few Db softer (which really isn’t that noticeable) and still have dynamics. Music that is squashed to achieve absolute maximum volume becomes rather lifeless and it can actually be damaging to your ears.
So audio mastering is a post-mix evaluation of the music where final tweaks to the sonic characteristics, EQ, compression, stereo imaging and final loudness are made. It is not an optional process. It is absolutely necessary if you want your music to sound like a finished master and also sound good on everything’s from an audiophile’s $10,000 stereo system to a pair of ear buds on an iPod or a cheap ghetto blaster.