Audio Production and Critical Listening

Technical Ear Training

Jason Corey

• Publisher: Routledge
• Year: 2016
• ISBN:
  9781317541042
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Acoustical Engineering
• Index: Technology & Engineering

Audio Production and Critical Listening: Technical Ear Training, Second Edition develops your critical and expert listening skills, enabling you to listen to audio like an award-winning engineer. Featuring an accessible writing style, this new edition includes information on objective measurements of sound, technical descriptions of signal processing, and their relationships to subjective impressions of sound. It also includes information on hearing conservation, ear plugs, and listening levels, as well as bias in the listening process.

The interactive web browser-based "ear training" software practice modules provide experience identifying various types of signal processes and manipulations. Working alongside the clear and detailed explanations in the book, this software completes the learning package that will help you train you ears to listen and really "hear" your recordings.

This all-new edition has been updated to include:

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• Audio and psychoacoustic theories to inform and expand your critical listening practice.

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• Access to integrated software that promotes listening skills development through audio examples found in actual recording and production work, listening exercises, and tests.

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• Cutting-edge interactive practice modules created to increase your experience.

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• More examples of sound recordings analysis.

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• New outline for progressing through the EQ ear training software module with listening exercises and tips.

Chapter 1
Listening

1.1 Everyday Listening

We are exposed to sound throughout each moment of every day regardless of whether we pay attention to it or not. Sound waves that reach our ears tell us about not only the sources producing the sounds, but also about our physical environment, such as the objects, walls, and other physical structures that may reflect, absorb, or diffuse sound. Unless we find ourselves in an anechoic chamber, reflected sound in our environment tells us much about the physical properties of our location. Our surrounding environment becomes audible in a sense, even if it is not creating sound itself, through patterns of sound reflection and absorption. Just as a light source illuminates objects around it, sound sources allow us to hear the general shape and size of our physical environment. The more we listen to everyday sounds, the more we become aware of subtle echoes, reflections, reverberation, low frequency rumble, flutter echoes, and so on. As our awareness of sound increases, we bring this listening skill back to our audio projects.

The frequency content and tonal balance of sound in our environment gives us some clues about the sound sources and also our proximity to them. A bass-heavy sound might emanate from a large mechanical device (such as a truck engine, airplane, or helicopter) or from natural sources (such as a waterfall, seashore, or thunder). Any echoes or strong reflections that we can hear tell us approximate distances.

Because we are primarily oriented toward visual stimuli, it may take some dedicated and consistent effort to focus our aural awareness. As professional audio engineers know, the effort it takes to focus our aural awareness is well worth the satisfaction in acquiring critical listening skills. The hard work does pay off. Although the concept of critical listening is relatively simple, the challenge lies in the practical application: focusing our attention consistently hour after hour, day after day on an audio project. It takes energy and discipline to listen with focus, but regular, targeted practice hones our awareness and gives us the ability to work more efficiently when tackling recording and mixing challenges.

We can develop critical listening skills everywhere we go, even when we are not actively working on an audio production. For instance, walking by a construction site, we may hear impulsive sounds such as hammering. Echoes—the result of those initial impulses reflecting from nearby building exteriors—may arrive fractions of a second later after the direct sound. The timing, location, and amplitude of echoes provide us with information about nearby buildings, including approximate distances to them. We can compare the timbre of direct and reflected sounds, especially in the case of long echoes. Perhaps some frequency content is being absorbed. Listening in a large music performance space, we notice that sound continues to linger on and slowly fade out after a source has stopped sounding, known as reverberation. Sound in a concert hall can be enveloping because it seems to be coming from all directions, especially at some distance from sound sources. We can notice the direction of reverberation and be aware of sound coming not only from performers on stage, but also reflected sound coming from all around us.

In another location, such as a carpeted living room, a musical instrument will sound noticeably different compared with the same instrument played in a concert hall. There are a few reasons for this difference. Physical characteristics such as room dimensions and surface treatments determine that a living room’s acoustical characteristics will be markedly different than those of a concert hall. The reverberation time will be significantly shorter and early reflections will arrive much sooner in a living room because the volume of a typical living room is much smaller than a concert hall. Floor covering can also influence spectral balance: a carpeted floor will absorb high frequencies and thus sound more dull, whereas a wood floor will reflect high frequencies and sound brighter.

The relatively close proximity of walls in a living room will reflect sound back toward a listener within milliseconds of the arrival of direct sound and at nearly the same amplitude. This small difference in time of arrival and near-equal amplitude of direct and reflected sound will create constructive and destructive interference at our ears. An extreme example of this effect is comb filtering (more in Chapter 3), where a sound is mixed with a single delayed version of itself. The effect is most apparent when we mix a sound with a delayed version of itself electrically or digitally (in a mixer). We hear comb filtering all the time in everyday life, but because reflected sound delay times are changing (as we move) and because there are so many delayed reflections arriving at our ears, the effect is smoothed out and we do not get the same deep notches in the spectrum that we do with only a single delayed reflection mixed with the original non-delayed sound.

Active listening is crucial to our work in audio engineering, and we can take advantage of times when we are not specifically working on an audio project to heighten our awareness of the auditory landscape and practice our critical listening skills. Walking down the street, sitting in a café, and attending a live music concert all offer opportunities for us to hone our listening skills and thus improve our work with audio. For further reading of some of these ideas, see Barry Blesser and Linda Salter’s 2006 book Spaces Speak, Are You Listening?, where they expand upon listening to acoustic spaces in a detailed exploration of aural architecture.

As audio engineers, we are concerned with capturing, mixing, and shaping sound. Whether recording acoustic musical instruments playing in a live acoustic space or creating electronic sounds in a digital medium, one of our goals is to shape sound so that it is most appropriate for reproduction over loudspeakers and headphones and best communicates the intentions of a musical artist. An important aspect of sound recording that an engineer seeks to control is the relative balance of instruments or sound sources, whether through manipulation of recorded audio signals or through microphone placement around instruments and ensembles. Sound source balances in a recording can have a tremendous effect on the musical feel of a composition. Musical and spectral balance is critical to the overall impact of a recording.

Through the process of shaping sound, no matter what equipment is being used or what the end goal is, our main focus is simply to listen. We need to constantly analyze what we hear to assess a track or a mix and to help make decisions about further adjustments to balance and processing. Listening is an active process, challenging us to remain continuously aware of any subtle and not-so-subtle perceived characteristics, changes, and defects in an audio signal.

1.2 What Is Technical Ear Training?

Just as musical ear training or solfège is an integral part of musical training, technical ear training is necessary for audio engineers, and it has applications in recording studios, live sound reinforcement, and audio hardware/software development. There are numerous technical references that describe audio engineering theory, yet ear training is equally as important as knowing the functionality of equipment on hand. Letowski, in his article “Development of Technical Listening Skills: Timbre Solfeggio” (1985), originally coined the term timbre solfeggio to designate training that has similarities to musical aural training but is focused on spectral balance or timbre. Technical ear training is a type of perceptual learning focused on timbral, dynamic, and spatial attributes of sound, especially with respect to audio recording and production. We can develop heightened listening skills that allow us to rely on auditory perceptions in a more concrete and consistent way. As perceptual psychologist Eleanor Gibson wrote, perceptual learning refers to “an increase in the ability to extract information from the environment, as a result of experience and practice with stimulation coming from it” (Gibson, 1969). Through years of working with audio, engineers generally develop strong critical listening skills. By increasing attention on specific types of sounds and sound processing, and comparing successively smaller differences between sounds, we can learn to differentiate among features of sounds. When two listeners, one expert and one novice, with identical hearing ability are presented with identical audio signals, an expert listener will likely be able to identify specific features of the sound that a novice listener will not. Through focused practice, a novice engineer can eventually learn to identify sounds and sound qualities that were originally indistinguishable.

Along this line, perceptual encoder developers found that their expert listening panel participants could more easily identify familiar distortions than unfamiliar distortions. Once we know what “warbling” or “metallic ringing” sounds like in an MP3-encoded song, the distortion is easier to hear, even if it is quieter relative to the signal (music). Suddenly all of our MP3s become difficult to listen to because we cannot stop hearing the encoder artifacts.

A subset of technical ear training focuses on the timbre of sound. One goal is to become more adept at distinguishing and analyzing a variety of timbres. Timbre is typically defined as that characteristic of sound other than pitch or loudness, which allows a listener to distinguish two or more sounds. Timbre is a multidimensional attribute of sound and is determined by factors including:

• Spectral content: frequencies present in a sound.
• Spectral balance: the relative balance of individual frequencies or frequency ranges.
• Amplitude envelope: the attack (or note onset time) and decay times of the overall sound and individual overtones.

A person without specific training in audio or music can distinguish between a trumpet and a violin sound even if both are playing the same pitch at the same loudness—the two instruments just sound different.

In normal everyday speech, we use timbre discrimination to identify vowels. Vowels sound the way they do because of formants, or spectral peaks, produced acoustically by the vocal tract. Our ears can distinguish one vowel from another with the first three formants. We give these various vowel sounds (timbres) names that correspond to specific letters. Since we map timbres to labels (vowels) seemingly automatically when we speak or listen to someone else speaking, we may not realize that we are already doing something that relates to technical ear training. With technical ear training we are simply adding a new set of timbres and associated labels to our inventory.

Classical music aficionados can name the instruments in an orchestra based on sound alone because of timbre, even going so far as to distinguish a C trumpet from a B♭ trumpet or an E♭ clarinet from a B♭ clarinet. Electric guitar players can easily identify the sounds of single coil and humbucker pickups. Techno and house music producers know the sounds of various models of drum machines from the timbres they produce. Popular music, although relatively straightforward in terms of melody and harmony, often uses complex layers of signal processing to produce tension and release. Timbral control from sophisticated signal processing has become one of the main artistic features of electronic pop music. In other words, the recording studio has become a musical instrument as recorded music employs more and more sophisticated treatment of timbre. With all of the audio processing options available, we have to be aware of much finer differences and an infinite number of possible sound colors on our palette.

Sound engineers work with much more subtle differences in timbre that may not be obvious to a casual listener. For instance, in comparing the sound of two different microphone preamplifiers or a 1 dB change in level, a novice listener may hear no difference at all. But it is the experienced engineer’s responsibility to hear such subtle details and make decisions based on them.

Professional recording engineers and expert listeners can focus their attention to specific auditory attributes and separate or discriminate them from the rest of a mix. Some musicians and composers have also trained their ears through experience to hear subtle attributes of audio mixes. Here is an anecdote about such a person. One time I was mixing a wind symphony recording, and the composer of the piece was present in the control room. This particular composer has extensive recording experience and has developed a high level of critical listening abilities for audio and sound quality. As we were listening to an edited version of his piece, he happened to notice a misplaced clave hit buried deep in the texture of the wind instrument and percussion sounds. It took me several listens to hear this very quiet clave hit, and of course I was a little embarrassed and frustrated that I could not hear it immediately. Once I heard it for myself, I could pick it out on each subsequent replay. This is exactly the kind of situation that requires us as engineers to develop and maintain the highest level of critical listening abilities.

Technical ear training focuses on the features, characteristics, and sonic artifacts that result from signal processing commonly used in audio engineering, including:

• equalization and filtering
• reverberation and delay
• dynamics processing
• characteristics of the stereo image

Technical ear training also focuses on unwanted or unintended features, characteristics, and sonic artifacts that may be produced through faulty equipment, particular equipment connections, or parameter settings on equipment such as noise, hum or buzz, and unintentional nonlinear distortion. Through concentrated and focused listening, an engineer should be able to identify sonic features that can positively or negatively impact a final audio mix and know how subjective impressions of timbre relate to physical control parameters. The ability to quickly focus on subtle details of sound and make decisions about them is the primary goal of an engineer.

Sound recording has had a profound effect on the enjoyment and evolution of music since the early 20th century. Sound recordings may simply document musical performances: an engineer records microphone signals as clean as possible with no processing or mixing. More commonly, based on record sales at least, engineers play an active role in guiding listeners’ attentions by applying intentional and dramatic signal processing, editing, dynamic mixing, panning, and timbral shaping to recordings.

In technical ear training, we focus not only on hearing specific features of sound but also on identifying the types of processing that cause a characteristic to be audible. To hear a difference between an equalizer engaged and bypassed is an important step in the ear training process, but it is even more helpful to know the specific settings on the equalizer. Just as experts in visual art and graphic design can identify subtle shades and hues of color by name, audio professionals should be able to do the same in the auditory domain.

Sound engineers, audio hardware and software designers, and developers of the latest perceptual audio encoders (such as MP3) all rely on critical listening skills to characterize audio signal processing and make final design decisions. Powerful audio measurement tools and research are bringing us closer, but objective measures do not always tell us if something will sound “good” to human ears.

One measure of equipment quality is total harmonic distortion or THD. Usually equipment designers aim to have THD levels as low as possible, but a THD level for one type of distortion may be much more audible than for another type of distortion. Loudspeaker designers and acoustics experts Earl Geddes and Lidia Lee (2003) have pointed out that high levels of measured nonlinear distortion can be less perceptible than low distortion levels, depending on the nature of the distortion and the testing methods employed. The opposite can also be true, in that low levels of measured distortion can be perceived strongly by listeners. Distortion produces new overtones ...