26. sound

Question 1

Sound energy def?

Answer 1

Travelling wave of air pressure changes

Question 2

Continuous sounds aka…?

Answer 2

Pure tones

Question 3

Pure tones/continuous sounds represented in what kind of wave?

Answer 3

Sin wave

Question 4

2 phases of sin wave for pure tones (cont. sounds) ?

Answer 4

Compression & Rarefaction

Question 5

Compression def? What does it look like on the wave?

Answer 5

High density, high pressure
Where molecules bump into each other
Upper part of the wave, the “peak”

Question 6

Rarefaction def? What does it look like on the wave?

Answer 6

Low density, low pressure
Molecules aren’t bumping into each other (as much)
Lower part of wave, “valley”

Question 7

How is a wave shown on a graph? What are the axes? (options…)

Answer 7

Y axis: air pressure
X axis:
- Time is most common
- Space (if you FREEZE time and measure from the origin of the sound expanding outwards/towards the ear)

Question 8

3 physical dimensions of sound? What are their perceptual correlates?

Answer 8

1. Frequency
2. Amplitude
3. Waveform
   –> Pure tone - simple sin wave
   –> Complex sound - all bumpy, combination of a bunch of different pure tones

1a. Pitch (freq.)
2a. Loudness (amp)
3a. Timbre (waveform)

Question 9

Wavelength def? (Is this super commonly used when discussing sounds?)

Answer 9

Time for ONE (1) cycle to be completed, from start to finish

NOT commonly used, much more common to use frequency

Question 10

Frequency def? Unit?

Answer 10

NUMBER of cycles per second
Unit: Hertz (Hz)

Question 11

Pitch def?

Answer 11

• the perceived highness or lowness of a sound
• perceptual correspondent to FRQ

Question 12

Amplitude def?

Answer 12

• Difference b/tw the max and min sound pressure in a sound wave
• physical aspect of sound –> related to the perceptual aspect of loudness

Question 13

Loudness def? depends on…?

Answer 13

• how intense or quiet a sound seems
• perceptual correspondent to amp
• depends on amp AND frq

Question 14

“Phase relations” –>
2 phases that exist for PURE tones within a complex sound?

Answer 14

In phase & out phase

Question 15

In phase def?
When does it happen/ what does it look like/ what’s going on?

Answer 15

• both component waves are in the same “side” of the graph
• both compressing or both rarefacting at the same time

Question 16

Out phase def?
When does it happen/ what does it look like/ what’s going on?

Answer 16

• the component waves are NOT on the same “side” of the graph
• doing opposite things
• kinda cancel each other out
• can create little pulsations
• this part of the sound is what makes you feel like its NOT a pure tone

Question 17

How do noise canceling headphones work?

Answer 17

• they produce noise that it out of phase with noise from the environment
• it cancels out, and you hear relative silence / quiet

Question 18

decibel (dB) definition? SPL meaning?
dB SPL meaning??

Answer 18

• A physical unit used to measure sound amplitude
• Uses LOGS of micro-pascals to convert into reasonable numbers
• SPL = Sound Pressure Level
• means that its the agreed upon standard where:
  –> Po is 20 micro-pascals
  –> 0 dB is the threshold for adult human hearing of a 1,000 Hz tone

Question 19

Fourier analysis def / what’s it for?

Answer 19

A mathematical procedure for decomposing a complex waveform into a collection of sine waves with various frequencies and amplitudes.

Question 20

What does a Fourier spectrum show? What does it look like? What are the axes?

Answer 20

• Shows the amplitudes at all frequencies that make up a complex waveform
• Looks like a BAR graph

X axis: Frq
Y axis: Amp

Question 21

Fundamental frequency def?

Answer 21

• The frequency of the simple wave produced by the simplest back-and-forth motion
• also the lowest frequency component of a complex sound

Question 22

Harmonics def? (where do they occur?) What is their numerical relationship to fundamental frq?

Answer 22

• A second/third/etc. part of vibration that is an EXACT MULTIPLE of the fundamental frq.
• They occur in instruments that have strings

Question 23

Harmonics example:
fundamental frq = 100 Hz
Give the first 2 harmonics. How much of the string is vibrating for each?

Answer 23

200 Hz –> 1/2 of the string
300 Hz –> 1/3 of the string

Question 24

Harmonics:
- What does the Fourier spectrum look like? (general slope)
- What does this mean for the relationship between amp. and frq.?

Answer 24

• angles down, tail to the right
• As frq increases, the amp. decreases
  ^ general trend, not rule all of the time

Question 25

Why do notes sound different on a flute, clarinet, and violin? What perceptual dimension of sound is affected?

Answer 25

• the relative strengths of all the harmonics are different
• this makes the timbre different

Question 26

How is amplitude measured/specified? What units? What is the equation?

Answer 26

• PRESSURE
• pressure (therefore amp) is measured in dB SPL
• dB SPL = 20 log (P/po) –> (p null)

Question 27

What is 0 dB?

Answer 27

Threshold for adult human hearing for a 1000 Hz tone

Question 28

How to measure sound level of increasing sounds / noises?

Answer 28

• CAN’T add dB
• only add pressures
• log (x + y) = log(x) + log(y)

Question 29

2 tones are played with the same amplitude, but they aren’t perceived as equally loud. Why does this happen?

Answer 29

• loudness depends on amp and frq
• we aren’t equally sensitive to all frqs
• sensitivity changes based on amp

Question 30

Audibility curve def? What are the axes? What’s the general shape? Lowest range?

Answer 30

• shows minimum amplitude at which sounds can be detected at each frequency
• shape is a U ish / V ish curve
• lowest range is between 500-5000 Hz
• any 2 points would sound the same

x axis: frequency
y axis: dB SPL (amplitude)

Question 31

Equal loudness contour def? What does graph look like? What are units and axes?

Answer 31

• curve shows the amplitude of tones at different frequencies that sound about equally loud
• Graph mirrors the audibility curve but moves higher up & flattens as it moves up
• Units = PHONS

x axis: frequency
y axis: dB SPL (amplitude)

Question 32

Phon def? Accounts for…?

Answer 32

• unit of loudness
• the loudness of a tone in phons is numerically equal to the amplitude of a 1,000 Hz tone that sounds equally loud–> ie if the loudness = 50 phons, then an equally loud tone of 1,000 Hz would have an amp of 50
• accounts for differential sensitivity to frequencies

Question 33

Timbre def?

Answer 33

• perceptual correlate of waveform
• differences in sound quality due to things other than pitch and loudness
• for complex sounds, mainly due to relative amplitudes of overtones / harmonics

Question 34

What 2 things does timbre depend on?

Answer 34

1. relative strengths of harmonics
2. “tone envelope”

Question 35

“Tone envelope” –> 2 components? Meaning? ex from class?

Answer 35

Attack rate and decay rate
Rate of the rise and decline of a note

Piano played backwards (diff. tone envelope) doesn’t sound like a piano anymore. Sounds like bagpipes