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How A Song is Professionally Mastered

In the fourth edition of our Rolling Stone Explainer series, we look at the process of Mastering and how it gets a song ready for release

In the earliest days of the record industry, the recording and Mastering were done live using mechanical processes.


Once a song has been mixed, the gears shift into Mastering – the final process before distribution. The goal is to polish a mix to its shiniest best and prepare it for listening on Streaming, CD or Vinyl. Mastering requires extreme critical listening, as most changes are less than 1-2dB across the frequency spectrum. Software tools exist to help the process; however, the final results are dependent on the mastering engineer’s skill, the accuracy of the speakers and the listening environment. The mastering stage involves signal processing with EQ, compression, saturation, stereo enhancement, limiting, and other final touches across the music’s final stereo file.

One of the Mastering’s original aims was to transfer the audio from the source containing the final mix to a data storage device (i.e. the master), which would be the source from which all copies of the song would be reproduced through pressing, duplication or replication. Recently digital masters have become the industry standard; however, a few engineers who specialize in analog Mastering still use audiotapes to store the final audio file. Mastering engineers also have to comply with specific loudness standards when creating digital masters.


In the earliest days of the record industry, the recording and Mastering were done live using mechanical processes. Performers sang and played into a large acoustic horn, and the master recording was created by the transfer of energy from the recording horn to a mastering lathe, which inscribed a groove into the surface of a rotating disc. These masters were usually made from wax. Until the introduction of tape recording, master recordings were almost always direct to disc, from which subsequent pressings were created. The introduction of magnetic tape in the 1940s enabled master discs to be cut separately in time and space from the actual recording process.  Through tape and other technological advances, the audio quality of commercial recordings improved dramatically past the 1940s. However, the constraints of the main commercial recording media, i.e. the 78 RPM disc, which evolved into the 45 RPM single and 33-1/3 RPM LP record, meant that audio quality, dynamic range and running time of master discs were limited, at least when compared to the subsequent arrival of the CD.

From the 1950s till the advent of digital recording, the mastering process went through several stages. Once the studio recording on multi-track tape was complete, a final mix was prepared to either single-track mono or two-track stereo tape. After the advent of tape, it was found that master recordings could be tweaked so that the resulting record would sound better. This was achieved by making fine adjustments to the EQ curve before cutting the master disc. The specialized staff technicians at large record companies who handled this process were the first mastering engineers with the job description as we see it today.

In the ’90s, the electro-mechanical taping process was largely replaced by digital technology, with digital recordings stored on hard drives or digital tape and mastered to CD. Digital Audio Workstations or DAWs became more common, allowing manipulating the master through a graphical user interface or GUI. The higher performance digital systems allowed mixing/mastering to be done at a peak sound level, which resulted in the loudness wars in commercial recordings, creating a reduction in audio fidelity and dynamic range through compression for the sake of increased volume.

In the last decade, mastering engineers such as Tom Coyne (10 Grammys with artists such as Adele and Bruno Mars) have taken the art of mastering to new heights. Tom passed away in 2017.


Today, a mastering engineer takes the stereo mix and corrects/enhances sonic elements to ensure the best playback quality across all systems. The balance that a mix achieves within a song is further enhanced through Mastering and across the different songs in an album that may have different producers and mixers. If songs 1-3 are pop, 4-6 ballads, and 5 hard rock, the mastering engineer decides the timbre, tone, and level to smooth the transition between these styles. Mastering engineers also have the responsibility to give the final touches to a project across a stereo mix. The restrictions of this format are what makes mixing essential and why the two work hand in hand.

Mastering engineers cannot go into a project to tweak a kick drum or filter a synth. They make broad adjustments and enhancements to the entire mix, keeping in mind the vision and market standards. Mastering engineers require attentiveness that no other person in the processes has. It is the last chance to change how something sounds and catch mistakes while being extremely careful about not ruining the composition.

The stereo file is processed using the tools described earlier, such as EQ, Compression and  Limiting. Additional actions, such as editing the length of the track, specifying gaps between tracks, fading in and out, noise reduction and enhancement processes are also part of the mastering stage. Lastly, a mastering engineer prepares music for distribution. This step includes sample rate conversion, bit depth reduction and adding required metadata. The songs, if in an album or EP, are also put into the proper order, i.e. track sequencing.  The finished master file is then sent out for distribution and future replications.


A mastering engineer’s role is vital to the commercial, radio-ready sound that most modern recordings need. In the playlist era, it’s more important than ever that your song’s sound stands out. However, Mastering can be an additional cost that many independent artists cannot bear. Many mixing engineers master their own music, and the creation of automated mastering services such as Landr has started to change the landscape of how songs are made commercially ready. You can have a great mix without a great master, and vice versa; however, you’d be unable to achieve a professional sound that can compete in today’s music world without both.

From Rolling Stone India