Transcript Week 7 - Truth Recordings

AUD202
Audio and Acoustics Theory
Psychoacoustics
Perception of Direction
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Upcoming Events
11 Days - NIHL Report
32 Days - Sound Observations Report
42 Days - Exam
Psychoacoustics
The study of the perception of sound
- How we hear
- How we can separate different sounds
- Our psychological responses
- The physiological impact of sound/music
Areas in Psychoacoustics
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Development of audio codecs
Perception of sound content
Auditory Illusions
Psychological effects of music therapy
Studies of what sounds/music people like
Localisation
Speech recognition
Some Psychoacoustic Effects
Binaural Beats
Masking Effect
Hass Effect (also called Precedence effect)
Binaural Beats
The Cocktail Party Effect
Missing Fundamental
McGurk Effect
Binaural Beats is the result of
playing two tones of closely spaced
frequency in opposite ears through
headphones.
The Cocktail Party Effect
The ability to focus listening on
a particular sound whilst
filtering out unwanted sounds.
Masking: Weaker sounds can become
inaudible in the presence of louder
sounds. The principle behind
‘perceptual encoding’ and mp3s.
Psychoacoustic Effects
Missing Fundamental: If we play a harmonic
series of pitches such as 2×f, 3×f, 4×f etc it
can give the impression that the fundamental
pitch is present.
The Haas Effect
The Haas Effect (Precedence Effect)
We localise sound based on the direction
of the first arriving sound. Additionally we
fuse the direction of subsequent
reflections with that of the original sound
despite the real direction of the reflected
sound.
The Illusion of Stereo
With one speaker, we only hear the direction of
one sound point.
With two speakers we hear a soundstage?
What are the limitations of surround sound
systems?
Perception of Direction
Can we localise the
direction of a sound’s
origin with only one ear?
Perception of Direction
Using two ears to localise a sound source is
called spatial or binaural localisation. This is
based on three acoustic cues received by the
ears:
1.Interaural intensity differences
2.Interaural time differences
3.The effects of the pinnae
Wavelength and Head Size
• Waves with a length less than the diameter of
the human head (17cm) will not diffract
around the head, so
• Waves with a length longer than 17cm will
diffract around the head allowing for
localisation using time differences.
Sound Localisation
Interaural intensity differences (IID)
for perceiving direction of high frequencies
Interaural time differences (ITD)
for perceiving direction of low frequencies
Sound Localisation
The pinna creates a delay used to determine
‘front to back’ and vertical panning due to the
shape of the pinna.
Psychoacoustic Effects
Scale Illusion
Phantom Melodies
Shepherds Ascending Tones
Falling Bells
Quickening Beat
Virtual Barbershop
Matchbox Rattle
McGurk Effect
Phantom Words
Doppler Effect
A moving sound source creates a pitch
change to a stationary listener.
As the sound comes towards the listener,
the pitch is higher. As the sound goes
away, the pitch is lower.
Doppler Effect
A moving sound source creates a pitch
change to a stationary listener.
As the sound comes
towards the listener,
the pitch is higher. As
the sound goes away,
the pitch is lower.
NOISE INDUCED HEARING LOSS
Noise Induced Hearing Loss
• Report due next Sunday (the 20th of April)
• 1000 words
• Remember: Title page, 12pt font, Arial or Times, 1.5x
line spacing, Reference & Bibliography sections,
Harvard Referencing.
• Use rubrics (on Moodle) to double check report
criteria.
Noise Induced Hearing Loss
• NIHL is acquired hearing loss caused by exposure to
excessive noise.
• Exposure to loud sound can cause the hair cells in
our inner ear to be damaged, resulting in noiseinduced hearing loss.
• Noise exposure charts can help to determine safe
noise levels
Noise Damage Indicators
If sounds seem muffled or softer after noise
exposure, your are likely experiencing a
temporary threshold shift.
If you are repeatedly exposed to excess noise
without protection, the shift can become
permanent and untreatable.
OH&S Principles
• Understand the noise level exposure time
chart and recognise when you are damaging
your hearing
• Limit your exposure to loud noise, otherwise
protect your ears with hearing protection
• Use your knowledge to help protect others,
e.g. young children, musicians etc