Attention and perception part 2 unit 10

Question 1

What is a sound wave?

Answer 1

A sound wave is created when an object’s vibrations cause pressure changes in the air, which are detected by the ears and interpreted by the brain.

Question 2

What is the difference between condensation and rarefaction in sound waves?

Answer 2

Condensation: Air molecules are pushed closer together, increasing pressure.
Rarefaction: Air molecules are pulled apart, decreasing pressure.
Together, they form the oscillations of a sound wave.

Question 3

What are the two main measurements of sound waves?

Answer 3

Frequency: How fast the wave vibrates (measured in Hertz, Hz). High frequency = high pitch.
Amplitude: How tall the wave is (measured in decibels, dB). Higher amplitude = louder sound.

Question 4

What is the range of human hearing?

Answer 4

A: Humans can hear sounds from 20 Hz (low pitch) to 20,000 Hz (high pitch).

Question 5

What is the audibility curve?

Answer 5

A graph showing how sensitive our ears are to different frequencies.
We hear sounds between 2000–4000 Hz best, even when they are very quiet (e.g., human speech).

Question 6

What is the threshold of feeling?

Answer 6

The point where sounds are so loud they cause pain or discomfort.
Example: A sound above 120 dB can hurt your ears.

Question 7

What are equal loudness curves?

Answer 7

A graph that shows how we perceive sounds at different frequencies and volumes.
Example: A low-pitched sound might need to be louder than a high-pitched sound to feel equally loud.

Question 8

What factors affect how we perceive loudness?

Answer 8

Auditory Response Area:

Sounds above the audibility curve are audible; below it, they are too quiet.
Example: A 30 Hz tone isn’t heard at 40 dB but becomes audible at 80 dB.
Threshold of Feeling:

Sounds above this threshold are felt rather than heard, causing discomfort or potential damage.
Equal Loudness Curves:

Different frequencies require different sound levels to be perceived as equally loud.
Example: A 100 Hz tone at 80 dB sounds as loud as a 1000 Hz tone at 80 dB.

Question 9

What is pitch?

Answer 9

Pitch is how high or low a sound feels.
High pitch = fast vibrations (high frequency).
Low pitch = slow vibrations (low frequency).

Question 10

What is the relationship between pitch, frequency, and tone chroma?

Answer 10

Pitch is how high or low a sound feels and is related to its frequency.
Notes with the same tone chroma (e.g., all “A”s) sound similar but differ in pitch.
Frequencies double with each octave (e.g., A₁ = 55 Hz, A₂ = 110 Hz)

Question 11

What is timbre?

Answer 11

Timbre is the unique quality of a sound that makes it different from others, even if they have the same pitch and loudness.
Example: A piano and a guitar playing the same note sound different because of timbre

Question 12

What is a sine wave in sound?

Answer 12

A sine wave represents the simplest type of sound wave.
It has a smooth, regular shape that repeats over time.

Question 13

How is pitch related to music?

Answer 13

Notes with higher pitch are played further to the right on a piano.
Example: The lowest note (A0) has a frequency of 27.5 Hz, and the highest note (C8) has a frequency of 4166 Hz.
As frequency increases, we perceive a higher pitch (this is called tone height).

Question 14

What is tone chroma?

Answer 14

Notes of the same letter (e.g., A1 and A2) have the same tone chroma and sound similar, even if their pitches are different.
Each time you move up an octave, the frequency doubles.
Example: A0 = 27.5 Hz, A1 = 55 Hz, A2 = 110 Hz.

Question 15

What is a pure tone?

Answer 15

A simple sound wave with only one frequency.
Rare in nature but can be produced by instruments like a flute or through whistling.

Question 16

What causes differences in timbre?

Answer 16

Differences in harmonics—the multiple pure tones that combine to create a complex tone.

Fundamental frequency: The lowest tone in a sound wave, which determines the pitch.

Harmonics: Higher-frequency tones layered on top of the fundamental.

Question 17

what is a complex tone?

Answer 17

when more than one pure tone is added together to produced a more complex waveform

Question 18

What are examples of timbre in everyday life?

Answer 18

The unique sound of different instruments (e.g., piano vs. violin).
Why people’s voices sound different from one another, even if they say the same word at the same pitch.

Question 19

How does timbre affect voice quality?

Answer 19

The combination of harmonics shapes the timbre of someone’s voice.
Example: A “nasally” voice has a different harmonic structure than a smooth one.

Question 20

What is auditory localisation?

Answer 20

The ability to determine where sounds are coming from in the environment.
Unlike vision, sounds don’t directly stimulate spatially distinct areas in the ear, so the brain relies on location cues.

Question 21

What are the two types of auditory localisation cues?

Answer 21

Binaural cues: Use information from both ears to determine left-right (horizontal) sound location.
Monaural cues: Use information from one ear to determine up-down (elevation) sound location.

Question 22

What is interaural level difference (ILD)?

Answer 22

A difference in sound intensity between the ears due to the acoustic shadow created by the head.
Works only for high-frequency sounds because low-frequency waves pass around the head without disruption.

means that a sound is louder in one ear than the other. This happens because your head blocks some of the sound from reaching the far ear, making it quieter on that side.

Works for high frequencies: High-pitched sounds (like a whistle) can’t bend around your head easily, so they create a bigger “shadow” (quieter sound) on the far ear.
Doesn’t work for low frequencies: Low-pitched sounds (like a drumbeat) can bend around your head, so both ears hear them almost equally

Question 23

What is interaural time difference (ITD)?

Answer 23

The time difference between when a sound reaches each ear.
Helps localise sound direction: sounds reach the closer ear first.
Most effective for low-frequency sounds.

Question 24

Why do ILDs work only for high-frequency sounds?

Answer 24

The human head is large enough to block high-frequency sound waves, creating an acoustic shadow.
Low-frequency sound waves are too large to be blocked, so they pass around the head without creating a shadow.

Question 25

How does (interaural time difference) ITD help localise sound?

Answer 25

If a sound comes from directly in front, the sound reaches both ears at the same time.
If a sound comes from one side, it reaches the ear closer to the source slightly earlier.
The brain uses this time difference to determine the direction of the sound.

Question 26

What are the two binaural cues for auditory localization?

Answer 26

Interaural Level Difference (ILD): The difference in sound intensity between ears due to the head creating an acoustic shadow, especially for high-frequency sounds.
Interaural Time Difference (ITD): The time delay between when a sound reaches each ear, helping determine the direction of the sound source

Question 27

What are monaural cues?

Answer 27

Cues that rely on information from one ear, used to determine sound location in the up-down (elevation) dimension.

Binaural cues only give us left-right information about sound location: monaural cues give us information about up-down (elevation) location, and only depend on one ear

Question 28

What is a spectral cue?

Answer 28

The main source of monaural information.
Sound waves from different elevations are altered by the shape of the pinnae (outer ear) before entering the auditory canal.
Different elevations cause different frequencies to bounce off the pinnae in unique ways, helping localise sound vertically.

Question 29

What evidence supports the role of pinnae in monaural localisation?

Answer 29

Experiments where molds were placed in the pinnae disrupted people’s ability to determine the elevation of sounds.
When the molds were removed, localisation abilities were restored.

Question 30

What are direct and indirect sounds?

Answer 30

Direct sound: Travels straight from the source to the ears (common outdoors).
Indirect sound: Bounces off objects in the environment before reaching the ears (common indoors). Auditory perception indoors is based on direct sound + indirect sound:

Question 31

How does the auditory system handle direct and indirect sounds?

Answer 31

It uses the precedence effect:
If the delay between direct and indirect sounds is short (5–20 ms), only the direct sound is perceived.
If the delay is long (>100 ms), the indirect sound is heard separately as an echo.

Question 32

What is the precedence effect, and how does it help us perceive sound?

Answer 32

The precedence effect helps us perceive one clear sound by prioritizing the direct sound over indirect sounds that are delayed by 5-20 milliseconds. This ensures accurate sound localization in small rooms. In larger spaces, indirect sounds may affect the quality of the sound, and in very large spaces (e.g., cathedrals), long delays can create an echo

Question 33

What is reverberation time, and why is it important?

Answer 33

The time it takes for a sound to decrease to 1/1000th of its original intensity (or drop by 60 dB).
Ideal reverberation time for concert halls: ~2 seconds, which balances sound clarity and richness.

Question 34

What happens when reverberation time is too short or too long?

Answer 34

Too short: The sound feels “dead” and lacks richness (e.g., poorly designed concert halls).
Too long: Sounds overlap, causing echoes that interfere with clarity (e.g., cathedrals).