Introduction
As recording, mix, and mastering engineers in music, film, video, and game sound environments, we are required to listen. We make decisions about recording techniques, mixing balances, and processor settings based primarily on what we hear. Therefore, we need to hear as accurately and consistently as possible. We are also faced with the challenge of translating between our auditory perceptions and the equipment parameters we can control. Although listening skills can also be applied to musicianship (pitch, tuning, ensemble) and conversations with our collaborators (for mutual understanding), this book concentrates on audio listening skills. The focus here is on technical attributes of audio: timbre or tone color (through equalization and filtering), dynamics processing (compression and expansion), level, reverberation, delay, distortion, noise, and mix balances, thus technical ear training. This book is the result of many years I have spent recording, mixing, thinking, learning, and most importantly, actively listening to technical attributes of audio. There is no easy way to gain critical listening skills. It takes regular effort over time through technical ear training to improve and maintain critical listening skills. This book offers methods, suggestions, things to think about, exercises, theory, and practical tips to help you develop critical listening skills.
The practice of audio engineering can be described as both an art and a science. As audio engineers, ideally we should understand audio theory and possess highly developed critical listening skills. Each recording project has its own set of requirements, and we cannot rely on the same recording/mixing/mastering procedures or techniques for every project. As such, we must rely on a combination of technical knowledge and listening skills to guide our work. Technical knowledge of analog electronics, digital signal processing, audio signal analysis, and audio theory (such as the principles of operation of microphones and loudspeakers) is critical for a solid understanding of audio engineering. Yet we place a great weight on what we hear rather than on strict technical parameters to make many of the decisions during an audio project, such as microphone choice and location, mix balance, fader levels, and signal processing. Audio theory gives us a solid framework within which to work and should be understood as much as possible, but in the end, many decisions are artistic or rely on personal taste. Our ability to navigate our subjective impressions of audio allows us to improve on sound quality and create mixes—both live and recorded—that deliver a desired artistic outcome.
Every action we take in relation to an audio signal will have some effect on the sound that listeners hear, however subtle it may be, and we must have our ears attentively tuned to the smallest details of timbre and sound quality. As engineers, we make decisions with a project’s artistic goals in mind, and must determine by ear if a technical choice is contributing to or detracting from these goals. We also need to know how the technical parameters of audio hardware and software devices affect perceived sonic attributes.
Alongside technical expertise, successful audio engineers can differentiate subtle timbral, dynamic, and technical details of sound. They can translate their aural impressions into appropriate technical judgments and alterations. Sometimes referred to as “Golden Ears,” these highly experienced audio professionals possess the extraordinary ability to focus their auditory attention and translate what they hear into efficient and accurate control of audio signals. They do not possess superhuman hearing from an audiological point of view. Their hearing is no better than average, but they are expert listeners with highly developed and discriminating critical listening skills who can identify subtle details of sound and make consistent judgments about what they hear. For example, an expert listener would accurately identify a small boost at a given frequency on an equalizer each time it is presented in a variety of applications (assuming monitoring conditions were sufficiently good). He or she would consistently know if the boost is there and be able to identify the parameter settings. Such experienced engineers identify shortcomings to be solved and features to be highlighted in an audio signal.
We can develop and improve critical listening skills gradually over time through day-today work on the job mixing or recording, as most in the industry have. But there are systematic methods that I believe can shorten the time required to make significant progress in ear training or at least give you a jump start on the process. As my own technical ear training professor at McGill University, René Quesnel, reported in his doctoral thesis, students who completed systematic technical ear training outperformed experienced audio professionals on tasks such as identifying frequency and gain settings of parametric equalization. Although it was once common for beginning engineers to work with more experienced engineers and learn from them in the context of practical experience, the audio industry has gone through drastic changes, and the apprentice model is disappearing from the practice of audio engineering. Despite this evolution in the audio industry, critical listening skills remain as important as ever, especially as we see audio quality decline in many consumer audio formats. The main distribution formats, MP3, AAC (Apple Music and iTunes Store audio format), and Ogg Vorbis (used by Spotify), are lower quality than the compact disc format of 44.1 kHz/16 bit linear PCM. This book presents some ideas for developing critical listening skills while reducing the time it takes to develop them.
A number of questions emerge as we begin to consider critical listening skills related to sound recording and production:
- What aural skills do experienced sound engineers, producers, tonmeisters, sound designers, and musicians possess that allow them to make recordings, mix sound for film, or equalize sound systems better than a novice engineer?
- What can experienced engineers and producers, who have extraordinary abilities to identify and manipulate sonic timbres, hear that the average person cannot?
- How do audio professionals hear and consistently identify extremely subtle features or changes in an audio signal?
- How do expert listeners translate between their perceptions of sound and the physical control parameters available to them?
- How can non-expert listeners gain similar skills, allowing them to identify the physical parameters of an audio signal necessary to achieve a desired perceptual effect?
- What specific aspects of sound should novice audio engineers be listening for?
There has been a significant amount written on the technical and theoretical aspects of sound, sound reproduction, and auditory perception, but this book focuses on the development of the critical listening skills necessary for the successful practice of audio engineering.
To facilitate the training process, software modules accompanying the book allow you to practice listening to the effects of different types of audio signal processing. The software practice modules allow a progression through various levels of difficulty and provide necessary practical training in the development of technical listening skills.
Audio Attributes
The main objective of this book and accompanying software is to explore critical listening as it relates to typical types of audio signal processing. Distinct from musical aural skills or solfège, technical ear training focuses on the sonic effects of the most common types of signal processing used in sound recording and sound reproduction systems, namely equalization, dynamics processing, and delay/reverberation/echo. When we know and can anticipate the effect of our signal processing, and we can discriminate between small changes in tone quality, we can have more effective control over the sonic results of our projects. Highly developed critical listening skills allow us to identify not only the effects of deliberate signal processing but also unintentional or unwanted artifacts such as noise, buzz, hum, and distortion. Once we identify such undesirable sounds, we can eliminate or reduce their presence.
The book is organized according to common audio processing tools available to the audio engineer. In this book we will explore the following main audio attributes and associated devices:
- spectral or tonal balance—parametric equalization
- spatial attributes—reverberation, early reflections, and panning
- dynamic range control—compression/limiting and expansion
- sounds or qualities of sound that can detract from recordings—distortion and noise
- audio excerpt cutoff points—source-destination editing
Goals of the Book
There are three main goals of this book and software:
- To facilitate isomorphic mapping of technical parameters and perceived qualities of sound. Isomorphic mapping is a linking of technical and engineering parameters to auditory perceptual attributes. As engineers, we need to be able to diagnose problematic sonic artifacts in a recording and have an understanding of their causes. In audio, we translate constantly between physical control parameters (i.e., frequency in hertz, sound level in decibels) and our perceptions of audio signals (i.e., timbre, loudness).
- To heighten awareness of subtle features and attributes of sound, and to promote a greater ability to discriminate among minute changes in sound quality or signal processing.
- To increase the speed with which we can identify features of sound, translate between auditory perceptions and signal processing control parameters, and decide on what physical parameters need to be changed in a given situation.
To achieve these goals Chapters 2, 3, 4, and 5 address specific types of audio processing and artifacts: equalization, reverberation and delay, dynamics processing, and distortion and noise, respectively.
Chapter 1 outlines the philosophy and goals of the book as well as the importance of technical ear training. There are some introductory listening exercises and, because hearing is so important to our work as audio engineers, we also discuss hearing conservation and ways to protect our hearing.
Chapter 2 focuses on the spectral or tonal balance of an audio signal and how that property is influenced by filtering and parametric equalization. The spectral balance is the relative level of various frequency bands within the full audio band (from 20 to 20,000 Hz), and this chapter focuses specifically on parametric equalizers.
The spatial properties of reproduced sound include the panning of sources, reverberation, echo, and delay (with and without feedback). Chapter 3 examines training methods for spatial attributes.
Dynamics processing is used widely in recorded music. Audio processing effects such as compression, limiting, expansion, and gating all offer means to sculpt audio signals in unique and time-varying ways. Dynamic range compression may be one of the most difficult types of processing for a beginning engineer to learn how to use. In many dynamics processing algorithms or circuits, the controllable parameters are interrelated, and this affects how they are used and heard. Chapter 4 takes a look at dynamic processing and offers practice exercises on hearing artifacts produced by these different effects.
Distortion can be applied intentionally to a recording or elements within a recording as an effect such as with electric guitars, but recording engineers generally try to avoid unintentional distortion such as through overloading an analog gain stage or analog-to-digital converter. Chapter 5 explores additional types of distortion, such as bit-rate reduction and perceptual encoding, as well as other types of sonic artifacts that detract from a sound recording, namely extraneous noises, clicks, pops, buzz, and hum.
Chapter 6 focuses on audio excerpt cutoff points and introduces a novel type of ear-training practice based on an audio editing technique. Listening for edit points and the amplitude envelope of a signal can sharpen our ability to differentiate changes in cutoff points at the millisecond level. The accompanying software module mimics the process of finding an edit point by comparing the end point of one clip with the end point of a second clip of identical music.
Chapter 7 examines analysis techniques for recorded sound. Although there are established traditions of the theoretical analysis of music, there is no standardized method of analyzing recordings from a timbral, sound quality, spatial image, aesthetic, or technical point of view. This chapter presents some methods for analyzing musical recordings and presents some examples of analysis of commercially available recordings. We also discuss listening bias and ways that we can make the listening process more objective.
There have been significant contributions to the field of technical ear training appearing in conference and journal articles, including Bech’s “Selection and Training of Subjects for Listening Tests on Sound-Reproducing Equipment” (1992); Kassier, Brookes, and Rumsey’s “Training versus Practice in Spatial Audio Attribute Evaluation Tasks” (2007); Miskiewicz’s “Timbre Solfege: A Course in Technical Listening for Sound Engineers” (1992); Olive’s “A Method for Training Listeners and Selecting Program Material for Listening Tests” (1994); and Quesnel’s “Timbral Ear-Trainer: Adaptive, Interactive Training of Listening Skills for Evaluation of Timbre” (1996). This book draws from previous research and presents methods for practice and development of critical listening skills in the context of audio production.
I have assumed that you have completed some undergraduate-level study in sound recording theory and practice and have an understanding of basic audio theory topics such as decibels, equalization, dynamics, microphones, and microphone techniques.
The Accompanying Software
All of the software modules are included on the companion website: www.routledge.com/cw/corey.
Because of the somewhat abstract nature of sound and critical listening, software practice and test modules are available via the companion website to help you practice hearing various types of signal processing that are described herein. The accompanying software practice modules are interactive, allowing you to adjust parameters of each type of processing and be given immediate auditory feedback, mimicking what happens in the recording and mixing studio. Although some of the modules simply provide sound processing examples, others offer exercises involving matching and absolute identification of processing parameters by ear. The benefit of matching exercises lies mostly in providing the opportunity to rely completely on what is heard without labeling the sound.
The use of digital recordings for ear training practice has an advantage over analog recordings or acoustical sounds in that digital recordings can be played back numerous times in exactly the same way. Some specific sound recordings are suggested in the book, but there are other locations to obtain useful sound samples for focusing on different types of processing. As of this writing, single instrument samples and stem mixes can be downloaded from many websites, such as the following:
- www.freesound.org
- www.royerlabs.com/royerdemocd1.html
- www.telefunken-elektroakustik.com/download/multi-track-session.php
- www.dpamicrophones.com/en/Mic-University/Stereo-Techniques/stereo-recordings.aspx
- www.cambridge-mt.com/ms-mtk.htm
Furthermore, software programs such as Apple’s Logic Pro and GarageBand include libraries of single instrument sounds that can serve as sound sources in the software practice modules.
This book does not focus on specific models of commercially available audio processing software or hardware but treats each type of processing as typical of what may be found among professional audio devices and software. Audio processing modules that are available commercially vary from one model to the next, and the training I discuss in this book serves as a solid starting point for ear training and can be extrapolated to most commercial models. What this book does not attempt to do is provide recommendations for signal processing settings or microphone techniques for different instruments or recording setups. It is impossible to have a one-size-fits-all approach to audio production, and my goal is to help you listen more critically and with more detail in order to shape each individual audio project.
Finally, I offer a word about “Golden Ears” and the ability to use audio effects processing. Assuming we have normal hearing, as determined by an audiologist, most people should be able to improve their critical listening skills through technical ear training. The renowned recording and mixing engineers do exceptional work not because they have superhuman hearing but because they have practiced listening day after day and year after year. It takes great effort and energy to listen intently and think about what we are hearing, but the effort pays off in better recordings and an ability to work faster and more accurately. It is not difficult to adjust parameters on a plug-in, but it is difficult to choose the parameters by ear and hear what needs to be done in each situation. In short, practice, practice, practice is the key to improving critical listening skills.