EE2215: Sound

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EE2215Sound Music Production for Broadcast

• Sound Fields
• Room Acoustic
• 3D sound effects

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Sound Field (1)

• Free Field
• A sound environment in which there are no
  appreciable effects on sound propagation from
  obstacles, boundaries, or reflecting surfaces.
• c.f. Anechoic Chamber
• http//www.sfu.ca/sonic-studio/handbook/Anechoic_C
  hamber.html

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Sound Field (2)

• Diffuse Sound Field
• A space with many reflecting surfaces and small
  sound absorption. Repeated reflections and
  diffractions of sound within a space result in
  good diffusion and a uniform distribution of
  sound energy.

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Absorption

• The loss or dissipation of sound energy in
  passing through a material or on striking a
  surface, usually through conversion to heat
  energy. The term may also refer to the property
  of a medium, material or object to damp sound
  energy. That part of the sound striking a surface
  which is not absorbed is either reflected or
  transmitted.

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Cancellation (1)

• The interference pattern that results from two or
  more sound waves travelling in the same space
  usually includes positions or times when the sum
  of the individual pressure variations approaches
  or reaches zero. This process is known as
  destructive interference or cancellation.

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Cancellation (2)

• In the simplest case, two signals that are 180
  out of phase will cancel. In environmental
  propagation, the points of cancellation are
  sometimes fixed and thus are experienced as dead
  spots, although this may also be caused by poor
  diffusion.

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Cancellation (3)

• A specialised case of cancellation occurs with
  two sounds in similar frequency, but 180-degree
  phase difference.

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Reflection

• If a sound is not absorbed or transmitted when it
  strikes a surface, it will be reflected. The law
  for reflection is the same as that for light,
  i.e. the angle of INCIDENCE of a SOUND WAVE
  equals the angle of reflection, just as if it
  were produced by a 'mirror image' of the stimulus
  on the opposite side of the surface.

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Parabolic Reflector

• A light rigid structure which reflects sound to a
  focus at which a microphone is placed. this
  focussing effect is very strong with wavelengths
  less than the aperture of the reflector, making
  it particularly suitable for recording high
  frequency sounds such as birdsong.

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Diffraction

• The phenomenon in sound propagation whereby a
  sound wave moves around an object whose
  dimensions are smaller than or about equal to the
  wavelength of the sound.

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Echo

• An echo is a repetition or a partial repetition
  of a sound due to reflection. reverberation is
  also reflected sound, but in this case, separate
  repetitions of the original sound are not
  distinguishable. for a repetition to be distinct
  from the original, it must occur at least 50 ms
  afterwards without being masked by either the
  original signal or other sounds. In practice, an
  echo is more likely to be audible after a 100 ms
  delay

c.f. reverb
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Sound Scape (1)

• An environment of sound (or sonic environment)
  with emphasis on the way it is perceived and
  understood by the individual, or by a society. It
  thus depends on the relationship between the
  individual and any such environment. The term may
  refer to actual environments, or to abstract
  constructions such as musical compositions and
  tape montages, particularly when considered as an
  artificial environment.

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Sound Scape (2)

• Since a sound scape is shaped by both the
  conscious and subliminal perceptions of the
  listener, sound scape analysis is based on
  perceptual and cognitive attributes such as
  foreground, background, contour, rhythm, silence,
  density, space and volume, from which are derived
  such analytical concepts as keynote, sound event,
  sound mark, sound object, sound signal.

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3D Sound Effects main effects

• Panning
• basic stereo-phonic effect (i.e. 2D)
• Reflection, Echo, Reverberation
• depth of sound space (e.g. Surround Sound)
• Reflection -gt phase inversion
• Echo -gt delay
• Doppler Effect
• 3D emulators
• 3D RSX (Intel's Realistic Sound Experience)

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Surround Sound (1)

• Cinema
• 2 channels for voice (front)
• 2 channels for sound (front-side)
• 1 - 2 channels for surround (rear)
• ambience, atmosphere and special effects
•  
• for compatibility with 2 or 4 channels systems
• without surround speakers, surround sounds are
  encoded.

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Surround Sound (2)

• home TV/video
• encoded surround sounds on video and laser discs
• gtgt DVD
• 5 channels (2 front, 2 rear, 1 bass)
• gtgt NICAM stereo
• (extra tracks for surround sounds)
• effecter "creates" surround sounds
• with a fixed logic like bass reflection bias

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Surround Sound (3)

• home TV/video
• When original source is not a multi-channel, the
  effecter "creates" surround sounds with a fixed
  logic like bass reflection bias. This may result
  a difference with the context on the screen.
• i.e. 2 ch stereo gtgt 5.1 ch stereo
• generating extra information
• 5.1 ch strereo gtgt 2 ch head phone
• reducing information

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Surround Sound (4)

• 5.1 ch stereo and direction of sound
• You can place the bass speaker anywhere in a room
  low frequency sound can NOT present the
  directionality.
• i.e. low frequency long wave length
• We need at least a ¼ wave length for the
  detection of pitch (phase) and direction.

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Surround Sound (5)

• Question
• Can you set up a surround sound system for a
  motor vehicle, in which all the passengers can
  enjoy the surround sound?

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References

• http//www.5dot1.com/
• http//www.headwize.com/tech/
• http//www.surroundmusic.net/
• http//www.sdds.com/
• http//www.audioholics.com/education/surround-soun
  d/dolby-digital-vs-dts-a-guide-to-the-strengths-of
  -the-formats