Preparing A Track For Mastering

You've poured your heart into your track, and your mix, and now it's time to send it to your mastering engineer. Before doing that there are a number of things to consider and check. 

Firstly, is it really finished? Fixing mix mistakes is something that can be very hard, or even impossible to do at the mastering stage. Make sure you are as happy as you possibly can be with your mix. If there are things you're worried about in your mix, perhaps things that you haven't been able to satisfactorily achieve, communicate this to your mastering engineer. There are some things that can be addressed in mastering (perhaps more than you might think) such as overall tonal balance changes, and a good mastering engineer will also be able to advise you about mix changes to resolve problems.

Secondly, have you left headroom and dynamics? Take a look at the picture below of example waveforms. 

The waveform coloured in green is an example of a perfect premaster. There are dynamics, and there is headroom to account for changes that will be made through processing. This means there would be complete freedom to use the processing seen fit to make your music sound as good as it possibly can sound. The waveform coloured in red is a far less than ideal premaster. This premaster has very little dynamics. It has already been limited/clipped which means processing choices would be more restricted (plus the mastering engineer would likely have better tools to achieve the limiting/clipping too). There is also no headroom, so this would have to be created. If you do work into a limiter/clipper as part of your writing or mixing process, be aware that this restricts processing that can be done at the mastering stage. It also increases the likelihood of introducing distortion, which can't be undone. It's a good idea to provide a premaster with the limiter/clipper bypassed AND a premaster with the limiter/clipper engaged for reference, if this is the way you work.

Thirdly, consider the top and tail, or the start and end of your track. Have you left silence at the top and tail for clean waveform starts and fades? In my experience, I've found that some DAWs can clip off the first few samples of a track, resulting in a nasty click or a softened attack, when rendering/bouncing a project that starts at the very beginning of the timeline. It's good practice to start your project a few seconds, or a bar, in from the start of the timeline to avoid this. Also, make sure to render plenty of silence at the end of your track to allow for reverb tails and fade outs.

Lastly, consider the file format. Lossless formats such as .wav and .aiff are preferable to compressed formats like .mp3. Compressed file formats result in a loss of information and possible audible artifacts as a consequence. Match the bit depth and sample rate of your original project when rendering/bouncing your premaster (usually 24-bit, 44.1kHz or 48kHz) to avoid possible degradation of the sound through conversion to lower bit depths and sample rates.

A final thing to note is that providing reference tracks from artists you like, or aspire to sound similar to, is absolutely fine, and often helpful.

By following these steps, you'll provide your mastering engineer with the best possible foundation to work with, and ensure your track shines on all platforms.