There are a number of simple things you can do to ensure that the audio file you are sending off for mastering is in the ideal format for creating the best possible master.
The first and most important thing is to ensure there is headroom remaining below 0 dBFS (digital zero). Ensure that the signal level on the master/output channel of your mixer never clips (hits 0 dB). Additionally, never use a limiter/maximizer plugin on the master channel, such as Waves L1 or L2 for example. By using these sorts of plugins, all you are doing is squashing and destroying dynamics in your track. If you're concerned your mixdown is quiet, don't worry! It will be much louder after it is mastered.
Here is an example of what an ideal mixdown will look like in an audio editor:
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A good basic rule when starting your mixdown is to set your kickdrum so that the peak signal level on it hits somewhere in the -8 dB to -10 dB range. This will leave plenty of headroom for the entire mix such that it does not clip the master/output channel in almost every case.
Often people like to compress their mixdown, and this can indeed give a nice effect with musical pumping/breathing to add to the groove. However a compressor set incorrectly can also ruin an otherwise good mixdown. As a fail-safe procedure, always render a backup copy of your song with the compressor bypassed so that the unprocessed option is available if needed.
Similarly, you may think the overall EQ of your track needs changing, and you may wish to insert an EQ on the master channel. This is almost always unnecessary - a large part of what the mastering engineer does is determine the ideal EQ/tonality for the song. Chances are the mastering engineer will have a better idea for what 'ideal' is, and will also have higher quality EQs to use. Remember that each process applied to audio also deteriorates the signal a small amount, and this deterioration is cumulative with each process! (a useful thought for mixing/producing in general as well).
In regards to file formats, always render/export/record your song at the native sample rate of your project, which in most cases will be 44,100 Hz. Always set your bit depth to at least 24-bit. All modern DAW software supports 24-bit or higher audio, and there is no excuse not to take advantage of it.
Following these simple guidelines will help keep your mastering engineer sane, and more importantly will ensure your tracks are the best they can possibly be once mastered.
Robin Petras
Sectionz.com Mastering Engineer
