Sound

1
Sound

• Characteristics

2
Soundwaves

• Sound begins as a vibration
• Pythagorus and Hippocrates hypothesized this
  around 0 C.E.
• Sound travels through a medium
• Through air at about 1130 ft/sec
• Through water at about 4 Xs faster
• Through steel at about 20 Xs faster

3
Soundwaves

• Consist of waves of energy.
• Compression when energy forces molecules closer
  together
• Rarefaction when molecules are pulled farther
  apart into a partial vacuum
• Air Loss Loss of energy due to friction of the
  sound wave through the air.

4
Sound Characteristics

• Frequency
• We interpret as pitch
• Frequency is the measure of how often a sound
  wave repeats itself
• Unit of measurement Hertz (Hz)
• Human range of hearing 20 Hz to 20,000 Hz
• Range of hearing depends on individual

5
Sound Characteristics

• Amplitude
• The energy of a soundwave
• Interpreted as loudness or volume
• Measured in decibels (dBs)
• 0 dB threshold of hearing
• 120 dB threshold of pain
• 60 dB normal conversation

6
Sound Characteristics

• Waveform
• The graphic representation of a sounds energy
  over time
• Simplest waveform is a sine wave

7
Sound Characteristics

• Phase
• The time relationship between two soundwaves
• Soundwaves are in-phase when they largely
  coincide in time (constructive interference)
• Soundwaves are out-of-phase when they largely
  dont coincide in time (destructive interference)

8
Sound Characteristics

• Wavelength
• The length of a soundwave
• ? V/f, where ? is wavelength, V is velocity of
  sound and f is frequency
• High frequencies have short wavelengths
• Low frequencies have long wavelengths

9
Sound Characteristics

• Harmonic Content
• Fundamental lowest frequency present in a
  musical tone
• Overtones all frequencies present in a musical
  tone other than the fundamental
• Harmonics overtones that are whole number
  multiples of the fundamental
• Overtones largely responsible for timbre

10
Sound Characteristics

• Acoustic Envelope
• 1. Attack (how a sound starts)
• 2. Internal Dynamics (energy changes after the
  attack)
• 3. Decay (how a sound ends)
• Aids in identifying the sound source instrument
• Can be divided into more than three sections

11
Acoustics and Pschoacoustics Terminology

• Linearity A comparison of how accurately a
  systems output duplicates the input
• Masking The hiding of one sound by another
• Complex waveform A waveform comprised of simple
  soundwaves (sine waves)

12
Acoustics and Pschoacoustics Terminology

• Equal Loudness Principle Equal amplitudes of
  different frequencies appear to be of unequal
  amplitudes
• Binaural Localization Determining the direction
  of a sound source by using two ears
• Precedence Effect We tend to determine the
  direction of a sound source from the first sound
  we hear
• Temporal Fusion When a reflected sound occurs
  less than 30 milliseconds after the direct sound,
  we perceive the two sounds as one
• Reverb Decay Time The time it takes a sound to
  decrease 60dB

13
Acoustics and Pschoacoustics Terminology
14
Reflected Sound

• Echo tells us about the size of the acoustic
  environment
• Reverb tells us about the texture of the acoustic
  environment
• Most of the energy we hear in sound lies in
  reverberation

15
ECHO

• Early reflections of sound
• Bounce off only one surface before reaching our
  ears
• Usually arrive less than 50 milliseconds after
  the direct sound

16
REVERB

• Later reflections of sound
• Bounce off more than one surface before reaching
  our ears
• Usually arrive after 50 milliseconds after the
  direct sound

17
The Ear

• Soundwaves first encounter the pinnae, the
  cartilage of the outer ear that directs or
  focuses sound down the ear canal
• The sound vibrations then reach the eardrum which
  passes them along to the middle ear

18
The Ear

• The middle ear (the ossicles) is composed of
  three tiny bones the hammer, anvil, and stirrup
• The ossicles are designed to amplify the sound as
  it travels toward the inner ear
• The ossicles are also designed to prevent damage
  to the inner ear
• The stirrup is attached to the inner ear at the
  oval window

19
The Ear

• The inner ears largest structure is the cochlea
  which is filled with a fluid
• Within the fluid is a smaller structure called
  the Organ of Corti
• Upon the Organ of Corti are tiny cilia which
  transfer the sound vibrations directly to neural
  synapses which in turn send the information to
  the brain as electro-chemical impulses

20
Studio Design

• Much of studio design is motivated by a desire to
  better control the process of recording as well
  as the product
• We can better control the process and product by
  utilizing acoustic isolation and multi-track
  recording techniques

21
Studio Design

• To accomplish better sound isolation we often use
  double thick structures
• We also use floating floors and walls
• We avoid such structures as
• Parallel surfaces
• Right angles
• Acute angles
• Concave surfaces