Today, more and more self-recording musicians and studios are catching on to the value of using an independent mastering engineer to master their finished mixes.  At a minimum, an independent mastering engineer provides an additional, objective set of “ears” in a recording project’s lifecycle.  But there’s much more to it than that.  Another major reason to use independent mastering engineers is to benefit from their experience.  A good mastering engineer knows that mixing and mastering are very different animals, and require very different mindsets.  They’re able to wear the “mastering hat” when mastering, while many others – even experienced recording and mixing engineers – just aren’t able to make that psychological switch.

As someone who masters a lot of songs for independent musicians and other recording studios, one of the most common questions I get is, “what should I send you, and how should I send it?”  Here’s a brief but handy guide to preparing your mixes for a mastering engineer.

What NOT To Send

First, let’s get a couple of misconceptions out of the way by explaining what you don’t need to send…  Most mastering engineers want to master from a single, stereo mix of the song and nothing else.  After all, that’s a huge part of that significantly different mindset between mixing and mastering: a mastering engineer wants to work from the finished recording, as it’s going to be presented to the listening public, rather than various pieces of it. As such, the two things you typically don’t want to send to a mastering engineer are: a) your DAW project file (e.g., from Logic, Cubase, Pro Tools, etc.); and b) “stems” of your final mix.

In the case of a DAW project file, it’s very doubtful a mastering engineer is going to have the same exact list of plug-ins and other processing that the project uses, so its output isn’t going to sound like your finished mix anyway.  But more important, mastering engineers don’t need to work at nearly that low a level, with all the various components of your mix; otherwise, they’re not really mastering at that point.  Instead, they’re really finishing your mix for you.  And if they are, then they should be getting mixing credit on your project, and be compensated accordingly.

Stems (aka, sub-mixes of different parts) of your mix are a little better (and closer to the finished mix), but are still not the full mix itself.  Some mastering engineers (but not most) are okay with working from stems (e.g., sub-mixes of drums, bass, all guitars, all keyboards, all lead vocals and all backing vocals, with all of their relative levels and processing already applied) because it gives them a little bit more flexibility and surgical control over the individual musical parts, but if they have to re-balance or apply special processing to one or more of the stems, they’re still finishing your mix for you, and should be credited and compensated as such.

A better, more practical, and more common approach (only if your mastering engineer asks) is to send just a couple of minor variations on your final, stereo mix, so that the mastering engineer can choose which of those versions to start mastering from.  Two common variations are lead vocal up/lead vocal down, and bass up/bass down.  For example, you might send a mix with the lead vocals where you think they should be, another mix with the lead vocals turned down a half-decibel across the board, and a third mix with the lead vocals turned up a half-decibel across the board. (You rarely would need to create a variation with the vocals turned up or down more than a decibel – that’s a LOT of change in volume from a mastering perspective.)  But these variations are still complete, stereo mixes, not pieces of mixes.  And it’s not necessary to create and send any of these variations unless the mastering engineer requests them.

Now that we’ve established that, most of the time, the only thing you need to send to your mastering engineer is your single, finished, stereo mix, let’s talk about details…

Preparing Your Mixes

In order to get the maximum sonic quality from your audio, your mastering engineer needs maximum-resolution mix files from you.  In geek-speak, that means they need “original-sampling rate (i.e., un-resampled), un-dithered, un-encoded stereo files at the maximum bit depth that your recording system will allow.”

As an example, if you recorded your project at 48 kHz, 24-bit resolution, then the stereo mix files you send for mastering should be no less than 48 kHz, 24-bit.  If you recorded your project at 44.1 kHz, 16-bit resolution, then the stereo mix files you send should be no less than 44.1 kHz, 16-bit.  In the case of bit depth only, if your recording system allows you to “render,” “bounce” or “export” your mixes at a higher bit depth than that of your individual tracks (e.g., 32-bit float), then use that higher bit depth when creating your stereo mix files.  More is definitely better when it comes to bit depth.

There’s no need to export your mix files at a higher sampling rate than the one at which they were recorded; in fact, that “upsampling” process can actually be detrimental, while adding absolutely nothing to the content of the audio.  So, if you recorded your project at 44.1 kHz resolution, DO NOT export your mix files at 48 kHz or some other higher sampling rate.  Leave them at 44.1 kHz.

Here’s a note of caution… As a convenient way to create “CD-standard resolution” files in a single step, many DAWs and other audio software allow you to apply certain final processing to the mixes as they’re being written to files.  The two most common processes are “resampling” and “dithering.”  Their main purpose is to reduce the resolution of files to fit them into a specific format, and that’s not something you want to do prior to mastering.  PLEASE TURN ALL SUCH OPTIONS OFF (or explicitly specify the final audio parameters yourself to avoid their “automatic” application)!  In particular, dithering prior to mastering can be very problematic because the process actually adds low-level, digital noise to the audio data that can’t be removed once it’s there.  If that noise exists, it will be mastered along with the rest of the musical information, which can result in nasty sonic “artifacts” in the final result.

Remember, the goal is to start with the absolute maximum amount of audio information in your files BEFORE mastering to preserve as much musical nuance, etc. as possible.  Any resampling, dithering, etc. (if even needed) should only be applied as the absolute very last step in the mastering process (using your mastering engineer’s very high-quality mastering tools) – never before.

Similar to resampling and dithering, most DAWs offer the option of applying extra audio processing to the final stereo “master bus” when producing a mix.  These typically include “finalizers,” “maximizers,” EQ (equalization), compression and limiting.  In essence, these are mastering-type processes, so unless their application is critical to your mixes’ musical sound, I recommend turning them off.  Or better yet, send two versions of your final mix: one with these “master bus” processes turned on, and one with them turned off.  Then your mastering engineer can decide whether to start with your “pre-mastered” version of your mix or not.  But keep in mind that a mastering engineer’s mastering-specific finalizers, EQs, compressors, limiters, etc. tend to be of higher quality than what many DAWs offer, so they’ll likely get you a better sonic result with their versions.

What Kind of Files To Send

You can send your stereo mix for mastering in any full-resolution file format, the two most common being WAV and AIFF.  PLEASE DON’T SEND AAC OR MP3 FILES!  MP3’s and AAC’s (iTunes’ default format) are severely data-compressed (“encoded”) files with a huge percentage of the audio data removed!  As with resampling and dithering, encoding should only be applied at the end of the mastering process.  Many mastering engineers use very high-quality MP3 and other encoding software that will give you much better-sounding encoded files than typical consumer encoding software.  For example, at Azalea Studios, we use the Fraunhofer MP3 encoding algorithm, and offer Fraunhofer-encoded MP3s at no charge to our clients as part of our mastering process.  That way, our clients don’t need to create their own (and probably, inferior-sounding) MP3s.  Whoever you use for mastering, make sure to ask them if they offer a similar service, and whether they charge extra for it.

How To Send Your Files

Full-resolution mix files are too large to send as e-mail attachments, but in today’s world, there’s no need to send mixes on a physical medium for mastering.  Instead, you can send your mix files using any of the Internet-based, large file-transfer/sharing services available.  Most of them offer a free option that allows you to send files up to a certain size.  I personally favor for my mastering clients.  It offers free file transfers up to 2 gigabytes in size, which is usually more than enough for an entire album’s-worth of full-resolution mixes.  If for some reason the total size of your final mix files is larger than 2 GB, simply send them in multiple transfers.  Other popular services include Dropbox, Google Drive, Hightail (formerly YouSendIt) and OneDrive.  Your mastering engineer should be able to work with any of them.

Other Helpful Info You Can Provide

The more your mastering engineer knows about the intended purpose of your mastered music, the better.  So, any information you can provide about what intended market(s)/genre(s) your music fits into, how the mastered results will be used (for radio airplay, digital download, film/TV cues, etc.), and how you expect it to be listened to (car stereo, headphones/earbuds, computer speakers, home hi-fi, etc.), will be invaluable to your mastering engineer.  If you foresee multiple genres, uses, and listening scenarios, that’s fine; by telling your mastering engineer about all of them, they’ll have the right information to make compromises and get you the best listening experience across the board.

Good Communication Is Key

In addition to the general stuff about how your music is going to be used, feel free to tell your mastering engineer anything else you think might be important about what you’re trying to accomplish with your music and your sound.  In fact, if your mastering engineer isn’t asking you about these things up front, you might want to look elsewhere.  The mastering process should be a two-way conversation, even if it’s brief and only happens once.  A mastering engineer who uses a “one size fits all” approach to mastering is probably not someone you want to hire.  A good mastering engineer will listen to your needs, understand what you’re going for based on their extensive experience, and then adjust their approach to achieve the best results for you.  My experience has been that if a good, two-way conversation takes place up front, mastering only takes one round, and everyone ends up extremely happy with the results.  If on rare occasions an additional round of mastering tweaks is required, your mastering engineer should be happy to make them for you.

Wishing you the best with your mastering – and all of your musical pursuits!

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