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Audio Mastering


What is mastering and the role of the mastering engineer?

This feature article is provided by ProSoundWeb
Mastering is essentially the step of audio production used to prepare mixes for the formats that are used for replication and distribution.  It is the culmination of the combined efforts from the producer, musicians, and engineers to realize the musical vision of the artist.  Each stage of the audio production process, from pre-production to mastering, builds on each other and is dependent on the previous process.  Mastering is the last opportunity to make any changes to positively affect the presentation of your music before it evolves from a studio environment to the outside world.

An awareness of the differences between the roles of mixing and mastering engineers should be noted.  While the tools may be similar, the perspectives between mixing and mastering are very different. When mixing, the focus is on the internal balance of individually recorded tracks and effects used both sonically and creatively for a single piece of music.

An album cannot be heard in its entirety until the job of a mix engineer is completed. The mastering engineer picks up where the mix engineer leaves off. Mastering is geared toward creating the balance required to make the entire album cohesive. The mastering engineer is most concerned with overall sonic and translation issues.  A mastering engineer works with the client to determine proper spacing between songs and how songs will be ordered on the CD. The flow of an album must appeal to the listener; it should engage them and take them on a musical journey as determined by the artist. Any final edits will be addressed during the mastering process as well.

Finally, the role of the mastering engineer is to provide preparation and quality control of the physical media send to the plant for replication.  This includes listening to the premaster CD to verify integrity, along with the more technical aspects such as encoding text, UPC/EAN and ISRC codes, checking for errors within the media and providing any necessary documentation such as a PQ list.

Is mastering always necessary?

A writer’s words are not complete until the editor approves them. A painter’s work is not complete until it has been matted and framed.  A musician’s work requires the same treatment. Audio production should not be rushed, finished haphazardly or completed “just to get it out there”. A finished product should reflect all of the work of the artist, producers and engineers that carry that vision forward.  Even a “perfect” mix needs mastering to a degree. In this case, you want the mastering to be as transparent as possible so that the original sound is maintained while preparing it for the final media.

As mentioned earlier, it is difficult for a mixing engineer to know how an entire album will sound in its entirety while mixing an individual track. In some cases a given track may be perfect on its own.  However, when that track is placed within the context of an album, slight adjustments in level or frequency balance may be required.  Given the amount of music distributed online, an album needs to stand out from start to finish to be noticed in such a competitive market. If the final goal is to create a product that is ready to be played on the radio, distributed online, or sold as a physical product, it should be mastered.

Mastering helps say something about the professionalism of the artist, from the arrangement of certain styles of songs to the volume of the recording to the pacing of the tracks. If an artist is serious about their music, they should make sure that someone with experience signs off on the finished product.

What kind of improvements can be expected from mastering?

Mastering can help to achieve the correct balance, volume, and depth for a style of music. It can add clarity and punch to music, giving it more vitality.  The idea behind mastering is that a product will sound better after it is treated by the mastering engineer. The degree with which a mastering engineer can achieve this is dependent on the given mixes. In some cases there may be limitations or compromises that need to be made.

One limitation of mastering is the inability to restore severely distorted material. Distortion in a mix is like corrosion; once present it cannot easily be removed and has permanently destroyed a part of the material.  While mastering can mask the effect of some types of distortion, it is essentially covering blemishes that should be addressed before the mastering stage. A common misconception is that mixes should be as “hot” as possible. With the advent of 24 bit digital technology there is no reason why mixes have to “go into the red.”

Most mastering engineers recommend a cushion of anywhere between -6 to -10 dBFS from peak level to help ensure that clipping does not take place and to allow room for processing.  In addition to peak level, the crest factor (peak-to-average ratio) is very important. While dynamic range can always easily be reduced, it is very difficult to undo the effects of over compression or limiting.
If the internal balance of a stereo mix is off, there may be compromises in the sound of the mastered track that will need to be made. For example, if cymbals or a vocal is very sibilant and bright while other parts of the mix are dark, it can be difficult to balance the overall sound in a way that enhances all elements.

In addition to frequency, levels between tracks may also be an issue. If the mastering engineer is given a stereo mix (as is usually the case) specific individual components of the mix cannot be completely isolated and processed separately.  While there are techniques such as de-essing, mid/side processing, equalizing or compressing for a specific imbalance, the results will likely not be as good as with a mix not having these issues and allowing the mastering engineer to address the balance on the whole.

One method of getting around internal balance issues is to provide alternate mixes. Some examples are vocal up/down mixes or mixes where one EQ is favored over another. Another method is supplying the mastering engineer with “stems” or sub mixes of the stereo track.  These might include a separate stereo mix of the vocals or instruments that when summed together are the same as the stereo mix minus any stereo bus processing.  In this case the mastering engineer is placed slightly in the role of a mix engineer and can make adjustments that wouldn’t be possible with a stereo mix alone. Another advantage with using stems is that alternate masters can easily be created such as radio edits, instrumental and vocal-only masters.

Another area where “fixing it in the mix” is better than “fixing it in mastering” is when dealing with the issue of noise. Mute automation on individual tracks should be used where there are noises during sections of a track that are not contributing to the mix.  Some examples are electric guitar hum/buzz on intros, outros, and breaks, bleed from headphones on the vocal track when the vocalist is not singing, drummers laying down their sticks after cymbals have faded but while other instruments are still playing at the end of a track.

What are some tips to help ensure the best possible master?

Audio quality can be very subjective. Before hiring a mastering engineer for a project you should have a clear objective on how you would like the finished project to sound.  Communication of these objectives between client and engineer is a key component to the success of a project. The language used to describe the character of audio can be ambiguous.  Terms like “brassy,” “fat” and “present” mean different things to different people.  One of the skills of a great mastering engineer is to able to translate this loose terminology into the specific technical processes required to achieve the client’s goals in a non-obtrusive way.

Some mastering engineers find reference tracks from clients to be helpful. Reference tracks can be worth a thousand words, because they serve to demonstrate the sonic objectives of the client.  My personal preference is to receive mixes that are as close as possible to what the finished product should sound like, but with enough leeway to be able to manipulate the sound in order to mold a cohesive album. Some general tips toward achieving this are:

  • Knowing your room and monitors. If you are using smaller nearfield monitors for mixing, be sure to listen to the mixes on a system that has extended bass to ensure that there are not low end bass problems.
  • If your monitors or room “color” the sound in any way be sure to compensate to ensure that the mix will translate well on other systems.
  • Fix track related issues before mastering. Listen for issues like excessive sibilance, uneven or exaggerated frequencies, phase or polarity problems, bad edits, depth and width of the sound field, and the relative levels of instruments and vocals.
  • I recommend listening to a mix in mono in order to hear if anything disappears or becomes exaggerated as well as listening to the mix at different levels and positions within your room. This can sometimes make an issue more obvious due to a different perspective.
  • Leave enough of the mix dynamics intact so that the engineer can make adjustments not only in the overall level but in the punch and clarity of the transients.
  • Don’t use any processing on the master bus that will interfere with processing that is best performed while mastering. This may include exciters and harmonic enhancers, EQ, normalization and limiting used to achieve a higher overall volume.
  • Leave the heads and tails of a mix intact so that there is room ambience before the music starts and enough of the music at the end to be able to tailor the fade out.
  • Having a bit extra at the start and end can also be useful so that a “noise profile” can be created for noise reduction systems that use this as a technique for removal of broadband noise.
  • Use mute and volume automation to remove extraneous noises from the individual tracks.

What should I send to the mastering engineer?

Mixes should be delivered in a format that alters the sound by the least amount.  For digital mixes, an uncompressed format (AIFF or WAV) should be used rather than compressed formats like MP3 or AAC.  You should speak to the mastering engineer that you will be working with to verify the formats that they accept.  I recommend staying with the same sample rate used in the original tracks, unless mixing through an external converter.  In that case, increasing the sample rate has its benefits. The bit depth should match the one used during the mix session rather than supplying tracks on audio CD where truncation and optionally dithering of the original tracks is applied.  I also prefer that digital mixes be sent as a single stereo interleaved file rather than split stereo files in order to help ensure phase coherence.

While a standard when sending analog tape for mastering, reference tones are becoming a lost art with digital.  If mixing through an analog board or to an external device, having an unaltered 1k reference tone (corresponding to 0 VU on the console) can help to identify issues where left and right channels are not calibrated or set properly.  If you are not attending the session, be sure to send all documentation regarding the sample rate, bit depth, format, and a listing of the filename with the full name of the song for each file.

Also note if there are alternate mixes of the same track (e.g. vocal up/down). A listing of the song order is also necessary along with requirements for song spacing and fades if not printed on the original mix. If CD text, UPC/EAN or ISRC codes are to be added to the final CD they must also be included in the listing.

Documentation may include information about your audio chain such as equipment and processing used (particularly if applied on the overall mix), what you feel are some of the enhancements that you would like to hear in each mix, along with any other information that you feel will be useful to the mastering engineer.

How much will mastering cost?

Prices vary depending on the profile and experience of the engineer, previous credits, along with studio costs and overhead. Typical rates are based on:

- Flat rate per album usually tiered based on the total number of tracks, sometimes with a total hourly cap.
- Flat rate per track or number of minutes per track.
- An hourly rate that can include additional costs for media due to time spent verifying and listening to the disc.

Some studios may also charge more for attended sessions versus non-attended sessions where the final product is delivered and approved by mail or Internet.

Costs for mastering vary anywhere from $10 per song to $500 per hour for well regarded professionals. Given that mastering is a subjective service-based business, as opposed to a commodity which can more easily be compared, caveat emptor applies.

Assuming that both quality and cost are considerations, set a realistic budget for mastering at the start of your project. Sometimes independent artists will not have anticipated the costs for mastering until a project is completed.  This forces them to use lower quality alternatives that are not necessarily best for their project. It’s a good idea to research the studios that will work within your budget. Call them to discuss the details of project and their approach.  In addition to gaining a better understanding of their process you will be getting a feel for the quality of their customer service. Some studios provide a demo of your material to ensure that they meet your expectations; others may charge for this service.  In either case, this is a good way to hear the quality of their work before committing to the cost of an entire album.

How much of a role does gear play versus the talents of a mastering engineer?

As the saying goes, “It’s the driver not the car”. A good engineer can work around limitations while a bad engineer will likely produce poor results, great gear or not.  This does not entirely discount the aspect of the gear. Having gear which is made specifically for mastering makes a big difference, not only in the quality of the sound, but in how quickly and easily the engineer can perform his work.  This includes equalizers, compressors and the usual components that most associate with the term “gear” as well as quality converters, monitors, and the room where the mastering engineer works.  Any of these can skew the perception of what an engineer hears potentially causing them to make decisions that wouldn’t happen given better accuracy.

There are many hardware and software companies claiming the ability to allow anyone without prior experience to use a particular preset, match frequency curves with references, or use other methods which will allow them to master their own music.  These “cookbook” approaches really miss the point of what the mastering process should be about. This approach cannot replace the skill acquired by an experienced engineer.

The processing performed should bring out the elements of the mix that are most important to each song. This requires both an artistic and technical evaluation.  Using a generic EQ or compressor setting to try to achieve this doesn’t address the individual characteristics of the song that make it unique or the specific problems that it may have in translating those elements.

What is the best (fill in the blank) for mastering?

This is a question that is often asked within mastering forums. The simple answer is that there are no “best” or one-size-fits-all solutions.  If there were, mastering houses would look more like a chain of department stores with the same type of room, monitors, and gear.  Just as the processing chain used for a particular piece of music will vary according to the character of that track, the hardware and software chosen by an engineer is based on his workflow and tastes.

There are however some common characteristics among mastering studios. The following are what I would consider the universal set of tools ranked in order of importance.

- A discriminating pair of ears. The ability to critically analyze issues that will interfere with the enjoyment and translation of a piece of music is the most fundamental tool of a mastering engineer.

- Knowledge and taste. Having the technical knowledge to be able address the problems heard in a mix and the taste to know whether or not to use a given technique.

- An accurate room and monitors. A good pair of monitors in a bad room can misrepresent a mix as much as a bad set of monitors in a good room.  Both room and monitors work together to produce a listening environment which will not distort the presentation of a mix causing an engineer to potentially make bad decisions.

- A transparent processing chain. As with physicians, one credo of the mastering profession is to “do no harm”. Mastering engineers go through great effort and expense to ensure that their processing chain is as distortion and noise-free as possible. Everything from the type of cables to the software and hardware used is analyzed and potentially modified to reduce any ill-effects caused by the processing chain.

- Processing which provides additional “color”. What would seem like a contradiction to a transparent chain is the addition of hardware or software which actually adds distortion in order to enhance a track. This includes both new and vintage hardware which adds tube distortion, transformer or tape saturation, along with software based modeling algorithms. The intent of these effects is to add warmth, thickness and depth to mixes that would otherwise sound thin or too “digital.”

Should you choose an engineer based on their “style”?

nevermindTen different mastering engineers working in the same room with the same equipment will create ten totally different masters, each sounding great on their own.  If you ask those same engineers to go back and reproduce any given master, you are likely to get ten almost identical masters back.  While each individual mastering engineer has his own style, it is important that he is able to separate himself from his style when needed.  An engineer should never let his personal taste interfere with the goal of the artist he is working with. Again, this is where communication with the client is a crucial element.

A good mastering engineer should be well versed in a variety of different categories of music. In general, there is no reason why an engineer known for creating great Country albums cannot produce a great Rock album.  While an engineer’s work should be able to transcend musical genres, if a mastering engineer has a certain style that is appealing to you as the artist, you should consider working with him.  It is important that both the engineer and the artist can communicate in a way that is complimentary to both individuals.

Which is more important, a technical background or musical one?

A mastering engineer should be well versed both technically and musically. The craft of the engineer is to be able to know good music and know how to make that music sound better.  Still, while a technical background is extremely important in the mastering world, that background should not interfere with the aesthetics.  Likewise, any personal feelings an engineer has about the stylistic choices of the music he is mastering should ultimately be discussed with the musician. It is because of this that an engineer’s musical background should not hinder his craft.

Given a technical background, some mastering engineers are capable of making modifications to equipment to create a more transparent sound, or provide color according to their taste and needs.  Having a musical background, particularly in the area of pitch, allows an engineer to identify frequency issues relating to musical notes and can speak directly to the musician about these issues in their terms.

An engineer should make sure that he strays away from favoring either background. While most engineers come from one or the other, their craft is in combining the two.  A mastering engineer should remain as objective as possible while still providing necessary feedback and insight from both a musical and technological perspective.

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