Fundamentals of Sound
MODULE 1: INTRODUCTION

 

 
Fundamentals of Sound: definitions and scope of study
Sound, Music, Noise: Essential and Operational Definitions
Basic Physical Variables and Units - Review

 

  

 

 

Fundamentals of Sound: definitions and scope of study

 

DEFINITIONS

The study of sound is a multidisciplinary field that deals with the physical (e.g. vibrations, waves), physiological (e.g. construction of the ear), and perceptual (e.g. auditory sensations) correlates of sound production, transmission, processing, storing, reproduction, and reception.
The study of sound forges a link among the physical, physiological, and perceptual frames of reference, examining ways in which physical and physiological aspects interact to give rise to auditory sensations/perceptions. ["Frame of reference": A collection of concepts/definitions accepted by a particular field or bounded area of discourse, representing a particular world view.]
 
Cognitive Psychology of Sound is an extension of this general study of sound, addressing implicit and explicit processes involved in the organization of sonic perceptions into meaningful wholes. It provides empirical support to the understanding of how we interpret and evaluate sound and sound structures, and is addressed in more detail elsewhere in the curriculum.

          For an alternative introductory resource relevant to our course, see Music & Science  [ Center for Music & Science; University of Cambridge ]

In our study of sound will delve into several of the Acoustics Fields:

Physical Acoustics (vibrational/physical frame of reference): examination of sound in terms of generation, transmission and modification of acoustic waves.
     How is sound produced and how is it influenced by sound source material, construction, and excitation?
     How does sound wave transmission through the air, etc. modify the sound before it reaches our ears? 
          What are the physical bases of our meaningful and emotional responses to sound?
     Out of the many relevant areas, we will be touching on Musical, Architectural, and Environmental Acoustics.

Physiological Acoustics (biological/physiological frame of reference): human body reaction to sound vibrations.
     How and with what accuracy do our ears process acoustic energy and how do they transform it into auditory sensations? 
          What are the physiological bases of our meaningful and emotional responses to sound?
     The combination of Physical and Physiological Acoustics outlines the discipline of Psychoacoustics.

Signal processing / Notation (symbolic frame of reference): examination of sound waves in terms of their electronic, graphic, and mathematical representations
(a special case of semiotics, to which music notation also belongs).
     How does manipulating analogues/symbols relate to manipulating acoustic waves and sound sensations, and vice versa?
          What is the formal basis of our meaningful and emotional responses to sound?
     In the context of our course, we will be limiting our investigation to a small subset of graphic representations of sound (i.e. sound signals & spectra)
     and to a conceptual understanding of digital audio basics.
 

In our study of sound we will identify

  1. sensation limits or absolute thresholds:
        absolute lowest/highest magnitudes (levels) of a vibration/wave that safely and reliably give rise to a corresponding sonic sensation
     

  2. relative sensation thresholds or difference thresholds or Just Noticeable Differences (JNDs):
        minimum amount of change in a physical variable, necessary to elicit a perceived change in sonic sensation
     

  3. type of relationship between physical and perceived changes
        (e.g. direct versus inverse relationship; linear versus nonlinear relationship; type of nonlinearity)
     

  4. changes in 1-3 due to a vibration's/wave's duration and level
        (e.g. issues of adaptation, fatigue, etc., related to the length and intensity of exposure to sonic stimuli)
     

  5. changes in 1-4 due to context and stimulus interactions
        (e.g. due to the simultaneous, past, or future presence of additional stimuli, whether sonic or otherwise)

 

 

Sound, Noise, Music:
Essential and Operational Definitions

 

Essential definition: a definition of a concept that
     (a) includes components that are both necessary (i.e. without them the concept would lose its identity) and
          sufficient (i.e. no other components are needed) to the concept's description, within a given context &
     (b) uniquely identifies it (i.e. no other concept shares exactly the same defining components), within a given context.
 
Operational definition: an essential definition of a concept that also
     outlines possible operations (i.e. numerical or other processes) that assist in the reliable identification and measurement of the concept's occurrences, within a given context.
 

 

SOUND

The term "sound" is often used loosely to refer to several phenomena/observations:
(a) An auditory sensation (perceptual frame of reference)
(b) The disturbance of a medium that may cause an auditory sensation (physical frame of reference) or
(c) An intended/desired auditory sensation (i.e. as opposed to noise) (cognitive/semantic frame of reference)
 
For this course, we adopt the following definition:
Sound is the sensation arising when sonic energy (i.e. vibrational energy within the response limits of the human hearing mechanism) reaches the ear.

Review the 3 video examples of sonic energy visualization.

 

 
NOISE

     The term "noise" is also used differently, depending on frame of reference (physics vs. communication) and context.
     While "noise" is subsumed under the broader concepts of "sound" and "signal," it is often approached in opposition to these concepts.
     In such cases, noise refers to "undesired" or "unfamiliar" sounds/signals.
     Then, there is the relatively new concept of Noise Music that challenges definition efforts (see the video below/right).

Noise as "Unwanted Sound"
 

Noise Music
 

Noise is:

(a) an auditory sensation arising in response to non-periodic sound waves/signals, with broad, flat, dense spectral distributions (vibrational/physical frame of reference--objectively measurable)

Noise is:

(b) an auditory sensation that is undesirable/unpleasant/unintended within a given context, interfering with auditory sensations that are desirable/pleasant/intended (i.e. sounds) within the same context (cognitive/semantic frame of reference--based on communication & subjectively measureable variables)

(image source)

In our course, we will be alternating between these two definitions, depending on ... context.

 

 
David Byrne (2012)
(short video interviews)
Book Review (The Guardian)

AUDIO BOOK: Part 1   Part 2
Jeff Tweedy (2020)
(podcast hosted by Malcolm Gladwell)

MUSIC

For the purposes of this course, we adopt the following operational definition:
Music is temporally organized sound and silence, a-referentially communicative within a context.

Emphasis is on the temporal and communicative aspects of music. Music is an essentially temporal and emotional art  [music as virtual time (S. Langer) - music as means for articulating our emotional dimension (J. Reimer)]. 
In listening to music, there is always some sort of response, some kind of behavioral change, indicating that we "received" and/or participated in the creation of something. What is received is an intention communicated in terms of patterning/configuring/organizing, akin to the prosodic dimension of language (prosody: the rhythmic and intonation aspects of language).

The importance of context is a direct consequence of music as communication. All communication involves shared and unshared knowing, and this is what we will broadly refer to as context.

Analogously to abstract animation, the potential of music to communicate a-referentially, that is without necessarily having to refer/point to anything other the sounds themselves, distinguishes it from linguistic communication. Music may be seen as a "noun-less" language, made only with verbs (potential / motion / action / narrative: all concepts with a fundamentally temporal dimension).

Model of musical communication - adapted from Kendall & Carterette,1990: 132.

MUSIC & COMMUNICATION

Understanding music involves interpretive translation across frames of reference, with music arising as the result of interaction (at some level) among composer(s), performer(s), and listener(s), broadly defined. 
Music, as a form of communication, is possible only when the parties involved share some common explicit (i.e. describable) and implicit (i.e. unspoken) knowledge. This sharing helps make the messages we infer, during a musical experience, relatively consistent and meaningful. 

Although a message usually implies an intent, communicated messages can be and often are different from intended messages, especially in the case of music with its a-referential (or self-referential) potential.
In addition, although some degree of shared knowledge is necessary for efficient communication, each communication event will always involve some degree of un-shared knowledge, explaining partly why there is no one-to-one relationship between a composer's intended message and a listener's constructed message. The term 'constructed message' implies that listeners are not passive observers.

Listening to music means configuring music. The act of listening involves a configuring operation that turns a series of incoming sounds into meaningful (to the listener) patterns, relationships, temporal wholes.
Listeners will always strive for pattern recognition and may identify patterns that were not intended during composition, even in the extreme case where no patterns were intended at all (e.g. aleatoric pieces of music; environmental sounds). 

The endless potential for new organizations and meanings to be discovered, by means of the configuring operations involved in listening, permits sonic works to outlive their composers, era, style, intensions, and contemporaneous cultural context. 

Sounds and sound patterns, alone, do not constitute music. The listener is the agent through whom sounds and sound combinations are elevated into music/art; the composer of a work can be considered its first listener and, at least in terms of music perception, this may be where their privileged status ends.
 

 

THE WORLD OF MUSIC
Sampling the depth and breadth of sonic and structural possibilities that can constitute music.
 
Additional resources:
Music across the world & The evolutionary bases of music (University of Cambridge)
The Music Instinct: Science & Song (PBS)
 

 
Excerpt from 'Raga Hameer'. Traditional piece arranged by Vilayat Khan. 'The Music of India and Pakistan' CD. The Rough Guide. World Music Network © 1995.

'Green Frog'. Arnhem Land; Northern Australia, Wangga song. A.Maralung: voice & clapsticks; P.Manaberu: didjeridu. 'The Garland Encyclopedia of World Music CD, Vol. 9: Australia & the Pacific Islands.' Garland Publishing © 1986.

'Caymmi Mostra Ao Mundo O Que A Bahia E Mangueira Tem'. Rio De Janeiro. Samba Enredo by Thobias Da Vai-Vai. 'The Music of Brazil' CD. The Rough Guide. World Music Network © 1998.

'Almamy Bocoum'. Senegal; West Africa. By Mansour Seck. 'West African Music' CD. The Rough Guide. World Music Network © 1995.
 
'Mauritania My Beloved Country'. Mauritania; West Africa. By Khalifa Ould Eide & Dimi Mint Abba. 'West African Music' CD. The Rough Guide. World Music Network © 1995.
 
'Jaya Semara'. Indonesian Gamelan for Kebyar gong. UCLA Gamelan Ensemble.
 
Three-part Bulgarian vocal piece. Fieldwork recording by Prof. T.Rice, UCLA.
 
'Jesu, Joy of Man's Desiring', from the Cantata 'Herz und Mund und Tat und Leben.' J.S.Bach (BWV 147). W.Basch: Trumpet; W.Rubsam: Organ. CD, Pro-Arte Records © 1986.
 
'Sonata No. 2 for Cello and Piano (1994) - II: Allegro', in "Schnittke - Complete Works for Cello and Piano - Alexander Ivashkin, cello - Irina Schnittke, piano" - Chandos Records Ltd. © 1998.
 
Excerpt from 'Symphony No. 21 - Opening' by Anton Webern (1927-1928).
 

 

 

Basic Physical Variables and Units - Review

Math Symbols & Units - (source)

 

Acoustics is based on the following three fundamental concepts/measures/units. All other acoustical concepts/measures/units derive from these three:
_ Mass (kg: kilogram)
_ Length/Distance (m: meter)
_ Time (s: second)

The International System of Units (SI), defines a total of 7 base units that also include:
_ electric current (A: Ampere)
_ thermodynamic temperature (K: Kelvin)
_ amount of substance (mol: mole)
_ luminous intensity (cd: candela)

Velocity:  v = ds/dt (change in distance per unit time) - Unit: m/s (meters per second).  
     Velocity of 1 m/s represents an increase in distance (away from a reference point) by 1 meter, each second.

Acceleration:  a = dv/dt (change in velocity per unit time) - Unit: m/s2 (meters per second-squared).
     Acceleration of 1 m/s2 represents an increase in velocity by 1 m/s, each second.

Force:  F = m*a (mass times acceleration).  In terms of gravity, a = g = 9.81 m/s2 and F = m*g - Unit: 1 Newton (N). 1 N = 1 Kg*m/s2.
     Force of 1 N represents the force that must be applied to a mass of 1 Kg in order to accelerate it by 1 m/s2.
     [ Newton’s Laws of motion: a) If F = 0, v is constant  b) F = m*a  c) Action – Reaction ]

Pressure:  P = F/A (force per unit area) - Unit: 1 Pascal (Pa). 1 Pa = 1 N/m2. = 1 Kg/(m*s2). 
     Pressure of 1 Pa represents a force of 1 Newton applied over an area of 1 square meter.
     Atmospheric pressure (at sea level): Patm = 105 N/m2. 
          Smallest pressure fluctuation that can be perceived as sound (limit threshold for pressure fluctuation) : Pref = 2*10-5 N/m2.

Work/Energy:  E = F*ds (work done by a force F when it moves a mass m over a distance ds) - Unit: 1 Joule (J). 1 J = 1 N*m. 
     If the mass is lifted at a height h, its potential energy (manifested as load) is: Ep = F*h = m*g*h. 
     If the mass is in motion with speed v, its kinetic energy (manifested as motion) is Ek = (1/2)m*v2. 
     1 J is the energy needed to move a mass of 1 Kg for 1 meter. 
          Types of energy: Mechanical, electrical, thermal, chemical, etc.

Examples:
 
Potential energy for a spring with spring constant K (measure of a spring's stiffness) displaced from rest by a distance y  --> Ep = (1/2)K*y2
Take-away: The energy stored in a spring is proportional to its stiffness and to the square of its compression/expansion away from rest.
 
Potential energy for a string with tension T and length L, displaced from rest by a distance y  --> Ep = 2T*y2/L
Take-away: Analogously to a spring, the energy stored in a string is proportional to its stiffness and to the square of its displacement away from rest but it is also inversely proportional to its length

Power:  W = E/t (amount of energy production/consumption/transfer per unit time) - Unit: 1 Watt (W). 1 W = 1 J/sec.
     Power of 1 W means that energy of 1 J is produced/consumed/transferred within a system every second.

In terms of hearing
a) Pressure is a more meaningful measure than Force and
b) Power is a more meaningful measure to hearing than Energy.
Intensity combines in a single measure the advantages (with regards to hearing) of Pressure over Force and of Power over Energy.

Intensity:  I = W/A (power per unit area) - Unit: 1 W/m2. 
     Intensity of 1W/m2 represents the production/consumption/transfer of 1 J of energy per second, through an area of 1 m2.

As an expression of the amount of energy in a vibrational system, Intensity is more meaningful and useful that Energy or Power because it allows for energy comparisons irrespective of a vibration’s duration or the spatial spread of the resulting wave. This matches the perceptual salience of rates of change over a given area rather than of absolute quantities, salience that is related to the auditory system's construction and function.
     Smallest vibration intensity that can be perceived as sound: Iref = 10-12 W/m2.

In vibrations and waves, Energy and, consequently, Power & Intensity are all proportional to the square of both frequency and amplitude.
     For waves in gases/liquids, intensity I is also proportional to the square of pressure: I = kP2 (where k is a constant).

  

Loyola Marymount University - School of Film & Television