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What is Mastering?

adapted from the iZotope Ozone guide to mastering.

Graphic EQ

UPDATE: This article is merely a brief introduction. Here are a few links to check out for more detailed information:

Mastering most commonly means the final step in the recording process, before the music goes off to be pressed into CD or vinyl format. It is a process that involves creating consistency among all of the tracks on an album so that they fit cohesively. This process is typically carried out by skilled audio engineers who have very trained ears. All record companies employ professionals who master all material, even if the mixing is spot on.

It is important to note that mixing and mastering are worlds apart. Recording and mixing all occur within the sequencer of choice, but mastering is applied to an audio file that is already mixed down, outside of the sequencer. My personal favorite choice of mastering tools is izotope ozone, because they offer the tools you will need: equalizer, reverb, multiband compression, volume maximization, stereo imaging, and harmonic excitation.

More and more today, bedroom producers are emerging, and they are taking on many roles, including songwriters, producers, recording engineers, and they are even mastering their own material. When you are on a tight budget, it’s impossible to afford the high prices of mastering services, so many of you would like to learn to master on your own. However, mastering is best when it is done by someone other than the producer, because you as a producer are too close to your own music. You won’t notice things that another pair of ears will notice, and therefore you may improperly master your own material without realizing it. If it’s possible, always get someone else to master your music. That being said, if you’re not going to get your music professionally mastered, at least learn how to mix and apply mastering effects to get the best sound possible.


First, what’s wrong with my song?

  • It’s not loud enough. It sounds wimpy next to other CDs. Turning it up or mixing down at a higher level doesn’t solve the problem. It sounds louder, but not, well LOUDER.
  • It sounds dull. Other CDs have a sparkle that cuts through with excitement. You try boosting the EQ at high frequencies, but now your song just sounds harsh and noisy.
  • The instruments and vocals sound thin. Commercial songs have a fullness that you know comes from some sort of compression. So you patch in a compressor and turn some controls. Now the whole mix sounds squashed. The vocal might sound fuller, but the cymbals have no dynamics.
  • The bass doesn’t have punch. You boost it with some low-end EQ, but that just sounds louder and muddier. Not punchier.
  • You can hear all the instruments in your mix, and they all seem to have their own “place” in the stereo image, but the overall image sounds wrong. Your other CDs have width and image that you can’t seem to get from panning the individual tracks.
  • You had reverb on the individual tracks, but it just sounds like a bunch of instruments in a bunch of different spaces. Your other CDs have a sort of cohesive space that brings all the parts together. Not like rooms within a room, but a “sheen” that works across the entire mix.

Don’t worry. It’s not that you’re doing anything wrong. There are just some things you still need to do to get that “sound”. You just need the right tools and an understanding of how to use them. You won’t become Bob Ludwig overnight (or probably ever) but you can make dramatic improvements in your master recordings with a little work.

Although there are many definitions of what “mastering” is, for the purpose of this tutorial we refer to “mastering” as the process of taking a mix and preparing it for manufacturing. In general, this involves the following steps and goals.

The “Commercial Sound”

The goal of this step is to take a good mix (usually in the form of a stereo file) and put the final touches on it. This can involve adjusting levels and in general “sweetening” the mix. Think of it as the final coat of polish, or the difference between a good sounding mix and a professional sounding master. This process can involve adding broad equalization, multiband compression, harmonic excitation, loudness maximization, etc. This process is often actually referred to as “premastering” but we’re going to refer to it as mastering for simplicity.

Consistency across the CD

Consideration has to be made for how the individual tracks of a CD work together when played one after another. Is there a consistent sound? Are the levels matched? Does the CD have a common “character”? This process is generally the same as the previous step, with the additional consideration of how individual tracks sound in sequence. This doesn’t mean that you can make one mastering preset and just use it on all the tracks so that they all have a consistent sound. Instead, the goal is to minimize the differences between tracks, which will most likely mean different settings for different tracks.

Preparation for Duplication

The final step usually involves preparing the song or sequence of songs for manufacturing and duplication. This step varies depending on the intended delivery format. In the case of a CD it can mean converting to 16 bit/44.1 kHz audio through resampling and dithering, and setting track indexes, track gaps, PQ codes, and other CD specific markings.

Mastering Effects

  • Compressors, limiters, expanders and gates are used to adjust the dynamics of a mix. For adjusting the dynamics of specific frequencies or instruments (such as adding punch to bass or warmth to vocals) a multiband dynamic effect is required, as opposed to a single band compressor that applies to the entire range of frequencies in the mix.
  • Equalizers are used to shape the tonal balance
  • Reverb can be applied to add overall sheen to the mix, in addition to the reverb that may have been applied to individual tracks.
  • Stereo imaging effects can adjust the perceived width and image of the sound field
  • Harmonic Exciters can add a presence or “sparkle” to the mix.
  • Loudness Maximizers can increase the loudness of the mix while simultaneously limiting the peaks to prevent clipping.
  • Dither provides the ability to upsample or downsample to different bit depths without sacrificing much quality.

Monitors
It’s important that you monitor on decent equipment when mastering. If your playback
system is coloring the sound, you can’t possibly know what’s in the mix and what’s caused by your playback system. That doesn’t mean that you can’t get decent results with relatively inexpensive equipment. The key is knowing the limitations of what you’re monitoring on and learning to adjust for it in your listening. For studio monitors, the most common problem is lack of bass, specifically below 40 Hz or so. These monitors just don’t have the size or mass to move that much air at a lower frequency.One solution is to complement a pair of studio monitors with a subwoofer. If so, make sure you adjust the subwoofer so that it doesn’t exaggerate the bass.
You’ll never get a perfect listening environment, and you can never predict how what you’re listening to will translate to the systems others will use to play back your song. With that in mind, here are some additional tips:

  1. Listen to music that you know well and have listened to on many systems. Spend some time “getting to know” your monitors. Play your favorite CDs through them. You probably know how these CDs sound on a home system, a car radio, etc. and this will help you learn to adjust your listening for monitors
  2. The bass will typically be under-represented on small studio monitors
  3. Monitors are very focused in terms of their soundfield, and imaging is typically more pronounced than on other systems.

Headphones
Headphones are another option for monitoring. There are entire sites and forums dedicated to headphones (such as http://headroom.headphone.com) so again we’ll leave out hardware recommendations and just advise you to ask around on forums. When working with headphones, here are a few things to keep in mind:

  1. Bass is sometimes under-represented on headphones, since bass on loudspeakers is often perceived from physical vibrations (what you feel), as well as from the acoustics (what you hear).
  2. Imaging on headphones is very different from imaging on speakers
  3. Equalization can be very different on headphones compared to loudspeakers. The listening room, your head and even your outer ear have filtering properties that alter the frequency response of the music. This “natural equalization” is bypassed with headphones. If you’re interested in learning more about this phenomenon, look into “diffuse field” headphones.

Seven Suggestions While Mastering

Before you jump into a marathon mastering session, here are seven things that are good to remind yourself of periodically:

  1. Have someone else master your mixes for you. OK, in most project studios we realize that the same person is often the performer, producer, mixer, and mastering engineer. At least get someone else to listen with you. Or find someone who will master your mixes if you master theirs. You’re too close to your own music. You’ll hear things other listeners won’t hear, and you’ll miss things that everyone else does hear.
  2. Take breaks and listen to other CDs in between. Refresh your ears in terms of what other stuff sounds like. OK, the pros just instinctively know what sound they’re working towards, but for the rest of us being reminded from time to time during the process isn’t such a bad idea.
  3. Move your listening position. Studio reference monitors are very focused and directional. The sound can change significantly depending on your listening position. Shift around a bit. Stand across the room for a moment.
  4. Listen on other speakers and systems. Burn a CD with a few different variations and play it on your home stereo system, or drive around and listen to it in your car. Don’t obsess over the specific differences, but just remind yourself what other systems sound like.
  5. Check how it sounds in mono. Check how it sounds with the polarity inverted on one speaker. People will listen to it this way (although maybe not intentionally) and while your master probably won’t sound great this way hopefully it won’t completely fall apart either. Ozone provides a quick check for this by clicking on the Channel Ops button. You can quickly switch to mono, switch left and right speakers, and flip the polarity of speakers.
  6. Monitor at normal volumes, but periodically check it at a higher volume. When you listen at low to medium volumes, you tend to hear more midrange (where the ear is most sensitive) and less of the lows and highs. This is related to something called the Fletcher-Munson effect, which involves how different frequencies are heard differently depending on the playback volume. So check from time to time how it sounds at different volume levels.
  7. When you think you’re done, go to bed, and listen again the next morning.