EE2215: Sound - PowerPoint PPT Presentation
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Title: 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
- Â
- 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
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