When we talk about audio mastering, we refer to the process of preparing a final mix for distribution. The purpose of this process is to make any corrections and post production to the mix, enhance and unify the sound, maintain consistency across the songs of a record and finalize the mix for distribution.
Beginner’s guide to mastering audio
To be able to achieve proper audio mastering, first of all you have to acquire a high-quality set of studio monitors. You need to focus on the details of the mix so that you can make the right decisions and accurately process the mix.
When you have all the individual tracks of your song mixed, you then have to export them to a single track. This final track is called the mixdown and it is the final form of your mix. When mastering, audio engineers prefer applying effects on a single stereo track than using the master bus of an entire session.
When you export your final mix, you have to maintain high bit-rate level, so that you can keep the quality of your track as high as possible which is usually the 32 bit-rate. You can convert your file to CD quality 16 bit-rate after you have finished the mastering process and you are ready to export your master file.
1 – First steps
Sound engineers use post equalization in order to boost or reduce certain frequencies of the sounds in order to maintain balance. The process involves taking a stereo file and adjusting the levels, adding equalization, compressing, stereo widening and limiting in order to make the song sound smoother.
Because most of the work was done during the mixing process, when mastering you don’t need to make any drastic changes in the equalization of the track. You can boost the low ends so that you can create a more stable and heavy sound and enhance the high frequencies to make the track brighter.
Frequencies around 120 Hz and 250 Hz usually cause the most problems considering noise and blurriness in a track, so you may want to consider experimenting and cutting some until you are satisfied.
2 – Picking the appropriate equalizer
When it comes to mastering EQ, most people tend to search for dedicated mastering equalizers. Although there are many equalizers built especially for using them in the mastering process, you can use any EQ available in your plugin library.
Many dedicated mastering equalizer plugin have some very useful features that common EQs so not. Try to search and find one that has a clean spectrum analyzer so that you can understand better the frequencies you need to teak and search for a clean interface.
Sometimes you need to consider using an equalizer that have a more subtle sound for your signal. This is because there are occasions that you need to avoid using equalizers that imitate the sound of hardware EQs in order to avoid saturation or distortion problems and create a cleaner result.
The choice is always yours. You have to decide whether you want a louder and brighter sound with a strong personality or a more subtle and clean one. When start, we would advise you to stick with the clean EQs until you have a better understanding of how mastering equalization works.
3 – Tweaking
Most audio engineers would suggest that you make very small tweaks to your track until you achieve the sound you want.
You should be using broad brush strokes so that you can enhance larger areas of your track and not smaller narrower ones that will cause certain frequencies to be burned and sound saturated.
There are no golden rules in mastering equalization, but it is a general perception that less is more. You need to be doing very small frequency changes of no more than 2 or 3db because most of the work has already been done in the mixing process.
Most times revisiting the original mix and making such changes and tweaks is a better choice, and you have better chances to achieve the sound you want without burning your sound and causing your track to sound noisy and flat.
4 – Boosting
Like stated above, when boosting your track you should use broad brush strokes in order to achieve smooth changes. You have to stick to low Q values so that you create big gentles curves to your equalizer and avoid causing any abrupt peaks.
This way you can make sure that the changes made to the track are more subtle and gentle, and that bigger areas are affected and boosted instead of narrower ones. This will cause different instruments to sound as if they were recorded together and will enhance the transparency of the song.
5 – Finishing the equalization
Final steps of the mastering equalization process, is to cut some of the lower frequencies. Most stereo sound systems go down to 30 to 40Hz so you have to consider taking out the frequencies below that level.
You can cut frequencies from 30Hz and below, but if you want to be completely sure that you maintain all of your lower end qualities, you can cut from 25 to 20Hz and below. Consider though, that even larger sound systems will go down to 40 or 30Hz at most, so you can be sure that you make the right move.
What is more, although humans cannot hear it, low frequencies move extremely slow and this can cause problems to the signal path and especially to the dynamic processors and limiters, preventing them from producing the appropriate loudness.
To make sure that you cut all these lower frequencies, apply more than one high-pass filters during the mastering process, so that you can achieve better results.
1 – Starting with compression
With compression, we can control the dynamic range of the track. Dynamic range is the variation of the song from its lowest volume to its highest volume.
When you start applying compression to a track, make very small changes in the beginning using a 2:1 ratio so that you can be able to hear clearly the changes of the sound. Experiment and add small amounts of gain to the track until you notice that the lower volumes start to sound better and louder parts are more balanced.
In order to avoid squashing the sound of the track, use the ratio level with caution. Start with a 2:1 ratio and increase only if you consider that it is absolutely necessary. Squashing may cause the track to sound flat, uneven and you will lose a substantial amount of information from your frequencies.
2 – Multi-band processing
Most multi-band compressors look really complex but in reality they are not. They are very useful tools that will help you process your track in much greater detail than common compressors and they can make it very easy for you to understand which frequencies need to be compressed more than others.
Nowadays, most Digital Audio Workstations (DAW) include their own multi-band compressors. Although there are significant differences both in the way they look but also in the way they can be used, most of the functionalities are similar.
You can use a multi-band compressor in the same way like you would use a common one. The main difference is that a multi-band compressor consists of a group of compressors, usually four to five under the same plugin feature.
Having the opportunity to use a separate compressor for each of the five different frequency areas gives you the ability to enhance or cut down those areas very accurately. As a result, you can have much more satisfying result than if you used a common compressor.
3 – How to isolate and tweak frequencies
Multi-band compressor give you the ability to isolate very specific frequency areas. To select the areas of your preference you can use the bands that are provided by the compressor plugins and place them in specific areas that you want to process.
Each band has its own volume levels, compression ratio and gain and this can be very useful as you can treat every frequency area in a very different and specific way.
Furthermore, each band offers the ability to solo or bypass the area selected so that you can preview and adjust your compression process.
You can also use multi-band compressors to boost certain frequencies in a very different way than you would do with an equalizer, as you can maintain the control of the dynamics and adjust their levels to make them sound louder and phatter.
When mastering a track, stereo processing can be complicated for some people. Using the right processor to achieve the best results possible is vital in this situation, as there are many processors that can be very useful during mixing, but not suitable for audio mastering.
Using a stereo processor that treats the entire frequency range of our track as a single band will do more harm than good to our track. This happens because most of the times the low ends of a track should remain intact so that we can keep a stable and strong basis.
The solution is to use a dedicated mastering stereo processor, with separate bands like in a multi-band compressor so that we can be able to make different changes in our selected frequency areas.
Setting the limiter
1 – Reference track
First things first. To start limiting our song we need another track to use as reference. You have to search a find a professionally mastered track of the same genre and feel, preferably one that you like.
Load the reference track next to your own track and listen to both of them. Compare and identify the differences considering loudness, brightness, widening and volume levels.
Start playing your track and experiment with different presets your limiter has to provide. This will give you an idea on how to proceed with your song and the changes you need to make so that you achieve similar results to your reference track.
2 – Limiter ceiling
Start setting the ceiling of your limiter by comparing your track to the reference track. Watch closely and adjust your ceiling so that the sound and leveling is similar to the reference track. Compare again and correct the levels so that they sound as close as possible.
3 – Threshold adjustment
Threshold is the tool that helps you set the level at which limiting begins. To limit bigger amounts of your mix you need to move the threshold slider down. This way, the sound becomes louder and phatter, because the gain make up is applied automatically as you go.
Focus on the levels of your track and compare them to the reference track once again. Try to get them as close as you can, without making excessive use of the threshold to avoid saturation and noise.
4 – Compare to the bypass and adjust
Make sure that you always compare the changes to the bypass version of your track. The more you limit your track the louder, brighter and crispier it becomes but if you overdo it, you may cause saturation and burn your track.
If you see that this is the case, you have to move up the threshold a little bit until your track sound clean again.
Revisit your equalizer, multi-band compressor and stereo widener processor to adjust the changes you made earlier. When limiting the quieter parts of the track stand out and you may have to reprocess them by equalization or compressing.
Finish and export
When the process is considered finished and you are satisfied, it is time to export your track. Convert it your file to 16 bit-rate and 44.1 Khz, which is the CD standard quality. You can apply this with every music software or DAW when you press the export button.
This will open the export window and there you can make these selections. The file formats vary between DAWs, but most of them if not all will work with Wav or Aiff formats. Those two formats offer the exact same quality of sound, so go ahead and choose the one that suits you best.
It is always a good idea to double check your final export for a last quality control check. There are music software available like Wavelab that can give you a better perspective of the file and highlight in a more advanced way the parts that need to be corrected.
Remember to check the sound of your mastered track in as many sound systems and listening environments as possible, so that you can have a better idea of how the track sounds and spot any misperfections.