psychoacoustics perception of direction aud202 audio and acoustics theory

PsychoacousticsPerception of Direction

AUD202Audio and Acoustics Theory

The Decibel

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11 Days - NIHL Report

32 Days - Sound Observations Report

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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