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Musical Acoustics

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What makes musical sounds an appealing means of expression? ... Strong harmonics - brash full and brassy. A-periodicity - non-harmonic overtones (cymbals,etc) ... – PowerPoint PPT presentation

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Title: Musical Acoustics


1
Musical Acoustics
  • http//www.aee.salford.ac.uk/
  • web page via student_area - undergraduate -
    musical acoustics
  • username students password module

2
Musical Acoustics
  • Questions to ask
  • What makes musical sounds an appealing means of
    expression?
  • How do instruments make musical sounds?
  • How can we make instruments sound better?
  • How can we imitate musical instruments and make
    new musical sounds?

3
Musical Acoustics Week1Physics, Perception,
Art
  • Aims
  • To outline how the physics of sound relates to
    its perception and the art of making music
  • Learning Outcomes
  • Appropriate definitions of sound and music
  • Classification of musical instruments
  • Understanding of the mechanisms of perception

4
Definitions of sound
  • a wave motion in air or other elastic media
  • the excitation of the hearing mechanism that
    results in the perception of sound

5
  • Sound is an oscillation
  • (stiffness and inertia)
  • Hearing is
  • frequency dependant (place theory)
  • sensitive - can detect ear drum motions 10-10m
  • has vast dynamic range 0dB to gt120dB
  • Signals processed by brain

6
Definition of music
  • The art of combining sounds so as to express
    thought or feeling to effect the emotions
  • All types of sound potentially musical hence
    catholic definition.

7
loud with discordant feedback for added
expression
melodic, ordered, refined sounds
Electronic synthesised sounds
(percussive, rhythmic sounds)
8
Experimental
Stockhausen
9
Classifying Musical Instruments
  • How can we build a taxonomy of musical
    instruments?
  • How do they vary?
  • What key features do they have in common?
  • How can this be a template to study, improve or
    emulate musical instruments?

10
Stringed Instruments
  • guitar, bass, violin, cello, sitar, etc
  • receives energy from say a pluck or bow
  • string oscillates
  • vibration tonally sculptured and amplified by a
    sound box

11
Wind Instruments
  • clarinet, oboe, trumpet, flute, etc
  • receives energy from moving air stream
  • modulated by the vibration or a read or lips
  • Air column oscillates
  • induces resonance's in pipe and bell

12
Physical Parameters and Perception
13
Definition of Pitch
Definition of Frequency
  • The number of complete cycles of a periodic
    process (e.g. waveform) occurring per unit time.
  • That attribute of auditory sensation in terms of
    which sounds may be ordered on musical scales
  • We can
  • distinguish between frequencies (JND)
  • associate pitch with harmonically complex sounds
  • describe discrete packets of sound as notes for
    sharing

14
Pitch / frequency dependence
  • Strongly correlated (Mels against Hz)
  • Though not linear or direct
  • lt 20Hz pulses
  • 27Hz to 5kHz musically useful
  • Double Bass (41.2Hz)
  • Middle C Piano (261.63Hz)
  • Piccolo (4725Hz)
  • gt10kHz whistle

15
Just Noticeable Difference in Frequency
  • depends on frequency, intensity and duration and
    person
  • Consider two tones of similar frequency played
    together, presented to
  • Separate ears JND 0.5
  • Same ears ( gt25 1/3 octave)
  • Why is this the case?

16
Place Theory
  • Sound creates Standing Wave in Basilar Membrane
  • Bands of hair stimulated to varying extents
  • Brain interprets resulting nerve signals
  • Hence ears act as frequency meter and spectrum
    analyser

17
Critical Bands
Equivalent Rectangular Bandwidth
18
Loudness/level dependence
  • Depends on frequency, duration and spectral
    balance
  • Dynamic range (Orchestra 70dB, CD 16bit 96dB)

19
Timbre / waveform dependence
  • Quasi-periodic bursts of acoustic pressure
  • Periodic complex waveforms can be deconstructed
    into simple harmonics (sine waves)
  • Weak harmonics - smooth, pure, flute-like
  • Strong harmonics - brash full and brassy
  • A-periodicity - non-harmonic overtones
    (cymbals,etc)

20
Problems with defining timbre
  • Each frequency harmonic component varies with
    time
  • Each harmonic component has its own pitch and
    loudness
  • The sensation of these components together highly
    subjective
  • (physical, anatomical, neurological,
    psychological)
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