Preparing for mastering

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Preparing for mastering

Mastering is the last stage in the music production process and it may be that you are coming to the end of the mixing stage and now looking into mastering and how to best prepare your audio for that procedure. I will run through some bullet points and then give some explanation as to why the suggestions are raised.

1)Deliver 24 bit files.
2)Deliver stereo interleaved files
3)Leave sample rate at the same rate as you have been working in your DAW.
4)Remove any limiters from your master bus.
5)Double check that there is no clipping of the master bus.
6)Check your mixes and make sure they are the best you can do.

So when you export your audio from your digital audio workstation ensure that you export at a minimum of 24 bit resolution. This is because this higher bit rate will be of value if the audio is being processed digitally during mastering. Whether your mastering studio is analogue or not this will still be preferred as there is almost always some form of digital manipulation that occurs and the higher the bit resolution the better the results sonically when any mathematics is performed on the audio. (i.e. plug in processing).Stereo interleaved files are preferred as the left and right channels in the audio are locked and when the audio is processed the phase coherency of the audio will be maintained as the left and right channels are processed in synchronisation. So whilst some digital audio workstations can export split mono, stereo interleaved is preferred.

Mastering studios should have the capability to transparently convert sample rates of audio so it is fine to leave the audio at the same rate at which you have been working. Common sample rates are 44.1kHz, 48kHz, 88.2kHz and 96kHz. Mastering engineers will have a range of limiters and as they all sound different they should be able to select the best one for your track. Some limiters have a characteristically brighter sound, some sound a little more dark, getting the limiter selection right is important so it is suggested that it is removed if you have been using one. In addition mastering engineers like some headroom in the file and if an audio file is hitting close to 0dBFS with a limiter it can damage peaks in the file which are impossible to rectify as there is virtually no headroom left for the processes that your mastering engineer will use.

When you remove a limiter please ensure you check the mix signal on your DAW master output bus does not exceed 0dBFS. (i.e. clipping) As soon as audio exceeds 0dBFS it means the maths representing the signal has run out of numbers and distortion of the waveform is the end result. If your signal does exceed 0dBFS you may simply pull down the master fader by the amount required in order to stop clipping occurring. In future it would be preferable to leave more headroom and apply  correct use of gain structure when mixing. (more on this later in this text)

Mixes should be nicely balanced with appropriate use of equalization and dynamic range control (compression/gating, de-essing). When mixing always try and give your ears frequent rests and come back and listen again with fresh ears (listening the following day is a good plan if time is not an issue). If you are unsure about your mixes consult with your mastering engineer, he or she might be able to offer some advice or at least some objectivity and a second opinion.

Gain structure during DAW mixdown:

Clipped mixes can be quite common, it means the signal has gone above zero on the DAW's output. This can be remedied at the beginning of a mixdown. Operate your DAW at 24 bit resolution (only worthwhile if your mix files are 24bit). At the start of your mix I suggest using a "peaky" instrument such as a snare or kick drum and peak it to -18dBFS on your master output. Use this as a reference instrument to mix against. Try not to adjust the level of the reference drum as you will then lose the reference, instead set it and balance all other mix elements against it. (if you need to add compression to the reference instrument use make up gain to get the level back to -18dBFS) This will give you an advantage of having ample headroom on your master output and greatly reduce the incidence of audio clipping the master output.

"What is audio mastering?" fact : Unintentional distortion during recording, mixing and mastering is one of the most unpleasant sounding audio problems and remains the most difficult to remove.Pay attention to red lights (LED's) on mixer channels and mic preamps when recording. It suggests the signal is distorting or close to distorting.

Sending files online:

When sending your files to your mastering engineer it is suggested that you use a loss less data compression algorhythm such as winzip or winrar/stuffit expander. These algo's use cyclical redundancy checks to ensure that the audio received at the mastering engineers studio is identical as that which you sent.Use an internet file sending website and do not try and attach large audio files to emails, they normally truncate any attachments in excess of 10Mb.When you send files it is always a courtesy to send an email from the same address you have used when uploading the files with some basic details so the engineer can tie the files up with your first communications.
Further information the mastering engineer will require:

For any given musical release the following information will be of great value

1)Running order of tracks.
2)ISRC codes.
3)Barcode No.
4)EXACT track names.
5)EXACT artist name/s.
6)Release title.

In addition when using an online mastering service it is of great value to the mastering engineer to hear your expectations or goals for the mastering of your music. So if you wish to supply a reference track for the music it can be helpful. (i.e. a band you would like your tracks to sound like) it can be of use to gauge what direction you expect mastering to move in. of course this is subject to the quality and character of the mixes supplied but in any event it will serve to give a general direction and pointers to the sound you aspire to.
©Copyright 2011 Barry Gardner
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