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How to Prepare Your Songs for Professional Mastering

09 Mar 2017

Interview kind: text · Reading time: 11 minutes

Mastering is the final step of the music production process. 
If you’re anxious to make your friends listen to a preview of your latest single, you can bounce a reference mix with all the limiters you like on it, but that’s not mastering. 
I could simply put a very fancy Peak Limiter Plugin on my master bus so that my perfectly mixed song sounds just as loud as the ones on the radio, why not? I’m afraid that’s not enough, in fact you should look for a real mastering engineer to polish your mix and make it really sounds like the ones on the radio.
Here are a few tips to make sure the mastering engineer you’ve hired can do his job properly.
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Mastering, what's that?
In the early ’40s, mastering wasn’t considered a separate step of the production workflow, for the simple fact that recording was a mechanical operation. 
The musicians were all recorded playing live in the same room and the master record was created by transferring their acoustic energy directly to the mastering lathe. The signal was captured with a large recording horn and transduced into mechanical vibrations with a diaphragm. 
These vibration were then directly cut into a rotating disc usually made from a soft metal alloy or from wax.
When reel-to-reel tape recorders started being widely used in the studios, that’s when mastering was really born. 
Recordings started being electrical rather than acoustic, the processing gear improved and a new sound storage medium took over the music business: vinyl record. 
It had different diameters and rotational speeds. In the ’50s, stereo recordings were introduced and different formats of vinyl records became the major music-consumption medium. 
The dynamic range of the mixes could go beyond the system's maximum capacity and that could mean you simply couldn’t play back certain sounds (the stylus would literally jump out of the groove). This required a dedicated engineer that had to make sure that the process of transferring the mix from tape to vinyl didn’t cause any of these sound issues. 
In the early stages, his job didn’t have to alterate the master tape and in fact he was simply called “transferring engineer”.  
But the grooves cut on the wax had a limited size related to the master’s stereo image and dynamic range, so the engineer started manipulating the sound to find the right balance between these two elements. 
There were limitations due to the vinyl's nature: more range meant wider cuts while a wider stereo image meant the stylus had to read through higher peaks and valleys. 
Another issue was the frequency response of the whole record, which gradually decreased throughout the playback because of the stylus that (of course) moved much faster on the outer grooves. The engineer started using specialized equalizers and compressors to deal with these problems and to make sure that the mix was not just simply transferred to vinyl, but it actually sounded at its best when played back. 
For example through compression he could increase the overall volume while shaping the peaks or through equalization he could gradually tweak the high-end. 
When CDs arrived in 80s, this new sound storage medium didn’t have the mechanical limitations vinyl had and mastering was no longer a step that had to be done to solve these issues. 
This process became more and more creative and it allowed engineers to add their personal touch to the final print. 
Their goal is to polish a mixed track by applying filtering or enhancing equalization, multi-band compression, harmonic distortion and a long list of other very specific operations that normal human beings can hardly hear. 
But at the same time our human ears are so use to hearing things that sound “good” and “mastered” that it would be impossible to avoid this part of the process.
Through the years mastering has been accomplished in dedicated rooms with a very detailed acoustic treatment to make sure the engineer gets the most linear frequency response from what he’s hearing. 
The mastering gear has become more and more sophisticated and powerful, but at the same time many engineers are still looking for that “warm sound” given by some very expensive pieces of vintage analog gear.
Leave some Headroom
As you may have just discovered, headroom is a part of your mix that mustn’t be underestimated. 
If the mastering engineer plays your session and the meters freeze at unity after the first kick hit, you can easily understand there’s not much he can do. 
How can he slightly adjust the frequency balance or the overall RMS of your song if everything is already sounding insanely loud and compressed? It’s usually a good thing to keep the peak level of your mix around -6 dBFS and a RMS level around -15 dB.
For many producers and engineers, master bus processing is part of the creative mixing process. Plugins and more powerful CPUs have made it easier to apply a fair amount of high quality emulations of some really high end gear to the whole mix. 
If you’re looking for someone else to master your songs, we recommend you bypass all of the signal-limiting processing and send them your stereo track with just the tools you used to “color” the mix in a certain way. 
It’s hard to compress a compressed track, or eq an eq-ed one. If you’ve used some creative compression or eq you really like, you could bounce a pre-mastered mix and send it to the engineer: make sure it’s properly labelled ad it has a PDF file attached that explains what that track is and why it’s in the pre-master folder.
How to Print Your Mix
Whatever mix software you’re using, you’ve obviously (and hopefully) routed all of the tracks or group buses through a stereo master bus, eventually controlled by a master fader. Once you’ve checked (and checked again) the headroom on your master meter, it’s time to print your mix.
- Create a new stereo audio track (and name it something like “Mix_PRINT”)
- Choose a free stereo bus (e.g. bus 25-26) as the output of your aux master bus (the bus where you send all of the tracks of your mix session)
- Choose the input of the “Mix_PRINT” track > bus 25-26
- Choose the output of the “Mix_PRINT” track > your usual master bus monitoring output
- Arm the track
- Record!
This process allows you to keep the processing you applied on the master bus (remember: no limiters!). 
Once you’ve printed your stereo master track, place it in a separate folder and name it correctly.
Mastering with Stems.
It’s become a common practice for many mastering engineers to work with stems rather than a stereo track of the whole mix. 
Of course, every mastering engineer will have his own opinion about this and (as you may have understood) nothing is mandatory in this crazy business. 
It’s a decision that’s usually made between the engineer and the artist/producer depending on the mix and on the final result they're aiming at. Some prefer to send just the stems of the whole sections of instruments (e.g. drums, bass, guitars, lead vocals, backing vocals and keyboards) while others may add some single tracks that might need some particular attention (e.g. kick and lead vocal).
Here are a few steps you can follow to print the stems of your song:
- Create a certain number of stereo audio tracks (e.g. “Drum_STEM”; “Guitar_STEM”)
- Route all of the single tracks to free stereo buses (e.g. all of the drum tracks > bus 27-28; all of the guitar tracks > bus 29-30)
- Set the input of the tracks you’ve just created so it matches the output of the single instruments (e.g. “Drum_STEM” input > bus 27-28; “Guitar_STEM” input > bus 29-30)
- Arm the tracks
- Record!
Make sure you route all of the send/return effects to the correct stem track (e.g. snare reverb > “Drum_STEM”). 
It’s likely that during your mix you’ve already routed the single tracks to group buses for bus processing or parallel bus processing. 
Just make sure you send these buses to the right stem track.
Once you’ve printed the stems, place them in a separate folder and name them correctly.
Once you have done all of that you are good to go! 
Send the files to your Mastering Engineer and wait for the magic to be done!
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