Psychoacoustics - Perception of Sound

Question 1

psychoacoustics

Answer 1

• Psychoacoustics is the study of the perception
of sound.
• Sound perception is influenced by physical,
biological and psychological factors.

Question 2

equal loudness principle

Answer 2

The Equal Loudness Study
– Originally developed by Fletcher & Munson
– Test subjects listened to pure tones at various frequencies in
10 dB increments.
– For each frequency and intensity, the listener also listened to a
reference tone at 1000 Hz.
– Fletcher and Munson adjusted the reference tone until the
listener perceived that it was the same loudness as the test tone.
– Loudness, being a psychological quantity, is difficult to measure,
so Fletcher and Munson averaged their results over many test
subjects to derive reasonable averages.
– Frequency response of our hearing at different levels.
– HEARING RESPONSE VARIES WITH FREQUENCY AND
LEVEL!

Question 3

Weighted Measurements

Answer 3

• Equal Loudness Curves
– “Weighted” measurements are used to approximate
human hearing response
– Weighting curves called “A” “B” & “C”
– A=40 phon curve, B=70 phon curve, C=90 phon
curve

Question 4

phon

Answer 4

• Equal Loudness Curves
– Phon is a term used in loudness levels for pure
tones
– 1 Phon = 1 dB SPL @ 1 kHz
– The number of phons is the dB SPL at 1 k Hz on
an equal loudness curve.
– For instance, if a sound is perceived to be equal in
intensity to a 1 kHz tone with an SPL of 50 dB,
then it has a loudness of 50 phons, regardless of its
physical properties.

Question 5

critical bands

Answer 5

• Critical Bands
– The ear’s frequency/loudness response is divided
into 24 frequency bands called critical bands –
each about 1/3 octave wide
– If two tones fall within a critical band the louder
will cover (mask) the softer and “beating” occurs

Critical Bands and Loudness
• Critical Bands
– Adding more tones within the critical band does
not increase perceived loudness until the tones
exceed the critical bandwidth.

Question 6

beat frequencies

Answer 6

• Beat Frequencies
– If 2 pure tones with a frequency difference of about 15 Hz
are combined the result will be a “fused tone” with
amplitude “beats”
– As the frequency difference gets less the beats will slow –
as the frequency difference gets larger the beats will
increase
– When the frequency difference is larger than the Critical
bandwidth combination tones are heard.

Question 7

constructive interference

Answer 7

Constructive interference occurs when the maxima of two waves add together (the two waves are in phase), so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes. Equivalently, the minima of the waves would be aligned.

Question 8

destructive interference

Answer 8

Destructive interference occurs when the maxima of two waves are 180 degrees out of phase: a positive displacement of one wave is cancelled exactly by a negative displacement of the other wave. The amplitude of the resulting wave is zero.

Question 9

combination tones

Answer 9

• Combination Tones
– a psychoacoustic phenomenon of an additional
tone or tones that are artificially perceived when
two real tones are sounded at the same time.
– When two pure tones with a frequency difference
larger than the critical bandwidth are combined
combination tones may be heard.
– Combination tones include the two original
frequencies plus the sum of the two frequencies
and the difference of the two frequencies

Question 10

masking

Answer 10

• Masking
– A louder sound will cover or mask a softer sound
– The frequency area masked by the louder sound is
called the masking shadow

• In addition to frequency masking there is
temporal (time) masking

– The masking phenomena is used in digital audio
data reduction (compression) programs such as
mp3

Question 11

Doppler effect

Answer 11

• Doppler Effect
– When a sound source is moving in relation to the
listener (or listener is moving in relation to the
sound source) the pitch goes up as they approach
and goes down as they move away

Question 12

McGurk effect

Answer 12

The McGurk effect is an illusion whereby speech sounds are often mis-categorized when the auditory cues in the stimulus conflict with the visual cues from the speaker’s face. A recent study claims that ‘skilled musicians are not subject to’ this effect.

Question 13

Haas effect

Answer 13

• The Haas (named after Helmut Hass) effect
has two important parts
• The ear/brain will use the first arrival to
located the sound source direction
• The ear/brain will fuse together sound
repetitions that arrive within about 30
milliseconds (depending on the type of sound)
of each other – Temporal Fusion

Question 14

temporal fusion

Answer 14

The ear/brain will fuse together sound
repetitions that arrive within about 30
milliseconds (depending on the type of sound)
of each other – Temporal Fusion

Question 15

precedence effect

Answer 15

The precedence effect or law of the first wavefront is a binaural psychoacoustical effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single auditory event; its perceived spatial location is dominated by the location of the first-arriving sound (the first wave front). The lagging sound also affects the perceived location. However, its effect is suppressed by the first-arriving sound.