Mastering (audio)

Mastering is a form of audio post production which is the process of preparing and transferring recorded audio from a source containing the final mix to a data storage device called a master recording, the source from which all copies will be produced (via methods such as pressing, duplication or replication). In recent years, digital masters have become usual, although analog masters—such as audio tapes—are still being used by the manufacturing industry, particularly by a few engineers who specialize in analog mastering.^[1]

Mastering requires critical listening; however, software tools exist to facilitate the process. Results depend upon the intent of the engineer, their skills, the accuracy of the speaker monitors, and the listening environment. Mastering engineers often apply equalization and dynamic range compression in order to optimize sound translation on all playback systems.^[2] It is standard practice to make a copy of a master recording—known as a safety copy—in case the master is lost, damaged or stolen.

In the earliest days of the recording industry, all phases of the recording and mastering were entirely mechanical processes. Performers sang or played into a large acoustic horn and the master recording was created by the transfer of acoustic energy from the diaphragm of the recording horn to the mastering lathe, typically located in an adjoining room. The cutting head, driven by the energy from the horn, inscribed a modulated groove into the surface of a rotating cylinder or disc.^[3] These masters were usually made from either a soft metal alloy or from wax; this gave rise to the colloquial term waxing, referring to the cutting of a record.^[4]

After the introduction of the microphone and electronic amplifier in the mid-1920s, the mastering process became electro-mechanical, and electrically driven mastering lathes came into use for cutting master discs (the cylinder format by then having been superseded). Until the introduction of tape recording, master recordings were almost always cut direct-to-disc.^[3] Only a small minority of recordings were mastered using previously recorded material sourced from other discs.

A finales de la década de 1940, la industria discográfica se revolucionó con la introducción de la cinta magnética . Esta cinta fue inventada para la grabación de sonido por Fritz Pfleumer en 1928 en Alemania, basándose en la invención de la grabación por hilo magnético por Valdemar Poulsen en 1898. No fue hasta el final de la Segunda Guerra Mundial que la tecnología se extendió fuera de Europa. La introducción de la grabación en cinta magnética permitió cortar los discos maestros por separado, en el tiempo y el espacio, del proceso de grabación propiamente dicho. ^{[ 3 ]}

Aunque la cinta y otros avances técnicos mejoraron drásticamente la calidad de audio de las grabaciones comerciales en los años de la posguerra, las limitaciones básicas del proceso de masterización electromecánica se mantuvieron, y las limitaciones físicas inherentes de los principales soportes de grabación comerciales —el disco de 78 rpm y, posteriormente, el sencillo de 7 pulgadas a 45 rpm y el disco LP ^de 33-1/3 rpm— significaron que la calidad de audio, el rango dinámico [ ^{a ]} y el tiempo de ejecución ^{[ b ]} de los discos maestros seguían siendo limitados en comparación con soportes posteriores como el disco compacto .

Desde la década de 1950 hasta la llegada de la grabación digital a finales de la década de 1970, el proceso de masterización solía constar de varias etapas. Una vez finalizada la grabación en estudio en cinta multipista, se preparaba una mezcla final que se transfería a la cinta maestra, generalmente mono de una pista o estéreo de dos pistas . Antes de la grabación del disco maestro, la cinta maestra solía someterse a un tratamiento electrónico adicional por parte de un ingeniero de masterización especializado.

Tras la llegada de la cinta magnética, se descubrió que, sobre todo en las grabaciones de música pop, se podían realizar grabaciones maestras para mejorar el sonido del disco resultante. Esto se conseguía ajustando con precisión la amplitud del sonido en diferentes bandas de frecuencia ( ecualización ) antes de la grabación del disco maestro.

En grandes compañías discográficas como EMI , el proceso de masterización solía estar controlado por técnicos especializados que eran conservadores en sus prácticas laborales. Estas grandes compañías a menudo se mostraban reacias a realizar cambios en sus procesos de grabación y producción. Por ejemplo, EMI tardó mucho en adoptar innovaciones en la grabación multipista ^{[ c ]} y no instaló grabadoras de 8 pistas en sus estudios Abbey Road hasta finales de la década de 1960, más de una década después de que los primeros estudios independientes estadounidenses instalaran grabadoras comerciales de 8 pistas. ^{[ 5 ]}

In the 1990s, electro-mechanical processes were largely superseded by digital technology, with digital recordings stored on hard disk drives or digital tape and mastered to CD. The digital audio workstation (DAW) became common in many mastering facilities, allowing the off-line manipulation of recorded audio via a graphical user interface (GUI). Although many digital processing tools are common during mastering, it is also very common to use analog media and processing equipment for the mastering stage. Just as in other areas of audio, the benefits and drawbacks of digital technology compared to analog technology are still a matter for debate. However, in the field of audio mastering, the debate is usually over the use of digital versus analog signal processing rather than the use of digital technology for storage of audio.^[2]

Digital systems have higher performance and allow mixing to be performed at lower maximum levels. When mixing to 24-bits with peaks between −3 and −10 dBFS on a mix, the mastering engineer has enough headroom to process and produce a final master.^[6] Mastering engineers recommend leaving enough headroom on the mix to avoid distortion.^[7] The reduction of dynamics by the mix or mastering engineer has resulted in a loudness war in commercial recordings.^[8]

The source material, ideally at the original resolution, is processed using equalization, compression, limiting and other processes. Additional operations, such as editing, specifying the gaps between tracks, adjusting level, fading in and out, noise reduction and other signal restoration and enhancement processes can also be applied as part of the mastering stage.^[8] The source material is put in the proper order, commonly referred to as assembly (or 'track') sequencing. These operations prepare the music for either digital or analog, e.g. vinyl, replication.

If the material is destined for vinyl release, additional processing, such as dynamic range reduction or frequency-dependent stereo–to–mono fold-down and equalization, may be applied to compensate for the limitations of that medium. For compact disc release, start of track, end of track, and indexes are defined for playback navigation along with International Standard Recording Code (ISRC) and other information necessary to replicate a CD. Vinyl LP and cassettes have their own pre-duplication requirements for a finished master. Subsequently, it is rendered either to a physical medium, such as a CD-R or DVD-R, or to computer files, such as a Disc Description Protocol (DDP) file set or an ISO image. Regardless of what delivery method is chosen, the replicator factory will transfer the audio to a glass master that will generate metal stampers for replication.

The process of audio mastering varies depending on the specific needs of the audio to be processed. Mastering engineers need to examine the types of input media, the expectations of the source producer or recipient, the limitations of the end medium and process the subject accordingly. General rules of thumb can rarely be applied.

Steps of the process typically include the following:

1. Transferring the recorded audio tracks into the Digital Audio Workstation (DAW)
2. Sequence the separate songs or tracks as they will appear on the final release
3. Adjust the length of the silence between songs
4. Process or sweeten audio to maximize the sound quality for the intended medium (e.g., applying specific equalization for vinyl)
5. Transfer the audio to the final master format (CD-ROM, half-inch reel tape, PCM 1630 U-matic tape, etc.)

Examples of possible actions taken during mastering:^[8]

1. Editing minor flaws
2. Applying noise reduction to eliminate clicks, dropouts, hum and hiss
3. Adjusting stereo width
4. Equalize audio across tracks for the purpose of optimized frequency distribution
5. Adjust volume
6. Dynamic range compression or expansion
7. Peak limit
8. Inserting ISRCs and CD text
9. Arranging tracks in their final sequential order
10. Fading out the ending of each song
11. Dither

A mastering engineer is a person skilled in the practice of taking audio (typically musical content) that has been previously mixed in either the analogue or digital domain as mono, stereo, or multichannel formats and preparing it for use in distribution, whether by physical media such as a CD, vinyl record, or as some method of streaming audio.

The mastering engineer is responsible for a final edit of a product and preparation for manufacturing copies. Although there are no official requirements to work as an audio mastering engineer, practitioners often have comprehensive domain knowledge of audio engineering, and in many cases, may hold an audio or acoustic engineering degree. Most audio engineers master music or speech audio material. The best mastering engineers might possess arrangement and production skills, allowing them to troubleshoot mix issues and improve the final sound. Generally, good mastering skills are based on experience, resulting from many years of practice.

Generally, mastering engineers use a combination of specialized audio-signal processors, low-distortion-high-bandwidth loudspeakers (and corresponding amplifiers with which to drive them), within a dedicated, acoustically-optimized playback environment. The equipment and processors used within the field of mastering are almost entirely dedicated to the purpose; engineered to a high standard, often possessing low signal-to-noise ratios [at nominal operating levels] and in many cases, the incorporation of parameter-recall, such as indented potentiometers, or in some more sophisticated designs, via a digital controller. Some advocates for digital software claim that plug-ins are capable of processing audio in a mastering context, though without the same degree of signal degradation as those introduced from processors within the analog domain. The quality of the results varies according to the algorithms used within these processors, which in some cases can introduce distortions entirely exclusive to the digital domain.

Real-time analyzers, phase oscilloscopes, and also peak, RMS, VU and K meters are frequently used within the audio analysis stage of the process as a means of rendering a visual representation of the audio, or signal, being analyzed.

La mayoría de los elogios a los ingenieros de masterización se otorgan por su capacidad para lograr una mezcla consistente con respecto a factores subjetivos basados ​​en la percepción de los oyentes, independientemente de sus sistemas de reproducción y el entorno. Esta es una tarea desafiante debido a la variedad de sistemas disponibles actualmente y su impacto en los atributos cualitativos aparentes de la grabación. Por ejemplo, una grabación que suena excelente en una combinación de altavoces / amplificador que reproduce audio de CD, puede sonar drásticamente diferente en un sistema basado en computadora que reproduce un MP3 de baja tasa de bits . Algunos ingenieros sostienen que la tarea principal del ingeniero de masterización es mejorar las conversiones de los sistemas de reproducción, mientras que la posición de otros es generar un impacto sonoro. ^{[ 9 ]}

• Premio Grammy al Mejor Álbum con Sonido Envolvente
• PMCD
• Guerra de volumen
• Era del álbum
• Remaster
• Incendio en los estudios Universal en 2008