What Is Mastering?

Updated: Aug 6

I recently became awarded an arts Council Grant which I am using to study mastering audio.

When I tell people this (not from the audio world) I am often met with a slightly perplexed look. What even is mastering? Even people from the music industry describe is as a dark art! So, it is not a well known vocation and really this is hardly surprising as it has only been around for the last 80 years.

I will try to explain in this next collection of blogs posts, the job of the mastering engineer, using terms and explanations that the average person will understand.

Today the mastering engineer's role is to take previously mixed audio and prepares it for use in distribution. This can be both in the physical domain (CD's or Vinyl) and in the digital domain (streaming or broadcasting).

So for this first blog entry in order to give a better understanding of the various audio formats that a mastering engineer must deal with. I will start with a brief history of recording (and mastering).

A Brief History Of Recording

The Acoustic Era (1877–1925)

In the early days of recording there was no requirement for a mastering engineer. The sound engineer would be there throughout the whole process, from recording to cutting straight onto wax or acetate disc. (1)

Before 1925, all 78's (vinyls) were recorded by the performers speaking into the horn of the gramophone as you can see from the example above. The ensuing vibration would cause the recording stylus to cut the wax of the master disc which could later reproduce a likeness of the original sound. These were called Acoustical Recordings. (3) The frequency range that could be reproduced by these records was small at around 250 hz - 2.5 khz. (hertz or kilohertz are cycles per second of an audio waveform - the smaller the number the lower the sound)

(To understand this frequency range in musical terms. On a piano, 250hz to 2.5Khz is approximately from just below a middle C up to the penultimate octave.)

Here an example of an Acoustical Recording:

The Electrical Era (1925–1945)

During this period recording technology improved by the introduction of Western Electric's integrated system of electrical microphones. (19) The introduction of these new technological elements meant that a wider range of sound and a variety of new techniques could be employed by the sound engineer. This process also increased the frequencies that could be produced to 50hz to 6khz (4)

(Approximately the entire range of a piano)

The disc cutting head was now electrically powered but the performances were still recorded straight to a wax “master' disc. (3) Therefore at this point, the job of the mastering engineer still did not exist.

Here is an example of the first commercially produced electrical recording that was made in 1925;

The Magnetic era (1945–1975)

In 1948, the magnetic tape was introduced (1) by Ampex (Model 200) and in 1935 the Electrical engineering company AEG introduced the first tape recorder called the Magnetophon K1 in Berlin. These discoveries were kept quite secret during the world wars as they were used in delivering propaganda in war time Germany. It was not until much later in the 1960's that the Phillip's Cassette tape became an acceptable consumer item. (7)

Before this happened Recordings on tape still needed to be transferred back to the medium of Vinyl.

The audio quality of tape had greatly improved from the earlier electrical recordings. Tape allowed for a bigger dynamic range (range of quiet to loud sounds) and frequency response (pitch). It also allowed for cutting and splicing (Editing).

When copying the audio from the tape back to vinyl these differences in audio quality needed to be addressed in order to prevent the mechanical problems that caused the needle to skip or jump on the vinyl. Audio compression (reducing the dynamic range) and Equalisation of the waveforms needed to be performed and this became the job of the mastering engineer. (3)

Once the studio recording on multi-track tape was complete, a final mix was prepared and dubbed down to the master tape, usually either a single-track mono or two-track stereo tape. Prior to the cutting of the master disc, the master tape was often subjected to further equalisation (A process by which the tone is changed by cutting or boosting frequencies) by a specialist mastering engineer.

The Digital Era (1975–present)

In 1978, Sony introduced the PCM-1600 Audio Processor which enabled digital recording to become commercially available to recording studios for the first time. (14). By the 90's, the use of digital audio workstations (Computer based recording) had become common place amongst recording and mastering engineers. (15)


The Compact Disc was invented in 1979. Electronics companies Phillips and Sony joined forces to turn this invention into an item for public consumption. In 1982 (8) the CD was made available to the consumer (First album released was The Visitors by ABBA) and there were many benefits to its use compared to vinyl. It could play 80 minutes worth of music, was less likely to be broken, you could skip to the next song and the audio quality was more consistent.

The main difference between the CD and previous audio formats is that rather than continuous analogue sound on a vinyl or tape, the audio was made from taking discrete samples of data.

The CD provided a digital version of audio whereby samples of audio data were taken at a certain resolution. This is called the sample rate and refers to the number of samples per second of a digital recording. (frequency) and audio Bit depth (dynamics). In the case of CD's, the bit rate was 16 bits sampled at rate of 44.1khz (44, 100 times per second)

So at this stage a music Mastering Engineer could now be expected to transfer from DAW's (Digital Audio Workstations – computers) or from reel to reel to the platforms of Cassette Tapes, CD's and Vinyl.

MP3' s

MP3's became available in 1993. (17) CD's were comparison were cumbersome and weighty and the audio on CD's and other digital storage types were too large to transfer easily via the internet. MP3's were also a much cheaper way of distributing music (17)

However, MP3's come with a downside. MP3 uses lossy data-compression to encode data using inexact approximations and the partial discarding of data. This allows a large reduction in file sizes when compared to uncompressed audio. (12) In order to reduce the data size, some of the audio file information is removed in as unnoticeably way as possible but if you were to then convert the MP3 back to a WAV file (A Wav file is an undegraded lossless audio file) the