Psychoacoustics Perception of Direction AUD202 Audio and Acoustics Theory
Dec 15, 2015
PsychoacousticsPerception of Direction
AUD202Audio and Acoustics Theory
The Decibel
Last Week >
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
• 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 BeatsMasking EffectHass Effect (also called Precedence effect)Binaural BeatsThe Cocktail Party Effect Missing FundamentalMcGurk Effect
Binaural Beats is the result of playing two tones of closely spaced
frequency in opposite ears through headphones.
The Cocktail Party EffectThe 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
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 Haas Effect (Precedence Effect)
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 thedirection 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 differences2.Interaural time differences3.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)Interaural intensity differences (IID)
Interaural time differences (ITD)Interaural time differences (ITD)
for perceiving direction of high frequencies
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 IllusionPhantom MelodiesShepherds Ascending TonesFalling BellsQuickening BeatVirtual BarbershopMatchbox RattleMcGurk EffectPhantom 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 noise-induced 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