L11 - Nature of Sound, Sound Sensitivity and Loudness

Question 1

What is sound?

Answer 1

• Variation in air pressure
• Wavelength: distance between one peak and the next (one peak to another)
• Frequency: number of pressure cycles per second at point in space (how fast it goes up and down)

Question 2

What is the comparison with light?

Answer 2

• Speed is slower = 340m/s, light is 300,000,000
• Wavelengths are larger = 1.7cm - 1.7m, light is 400-700nm
• Frequencies have a higher range 20-20,000Hz, light is THz (smaller range as it is what the sun emits)
• Sound transmissions from place to place can cause delays
• The perception of different frequencies is much more significant for hearing

Question 3

What are waves like?

Answer 3

• They ripple from a source, spherical wavefront from the source heading in every direction
• Sound waves radiate in three dimensions

Question 4

Psychological terminology in sound?

Answer 4

• Frequency = pitch: Sound can vary in frequency e.g sine wave can go up and down more rapidly = higher pitch and vice versa. Physically frequency changes, but psychologically pitch changes
• Frequency is measured in Hertz
• Amplitude, intensity and sound level = loudness (psychological) = troughs get higher and higher = gets louder
• Amplitude is variation pressure of air over time = measured in Pascals (Pa) = measured by standard deviation
• Intensity is amount of energy in the sound (square the amplitude) = measured in Watts/m2, also known as pressure variance
• Sound level is measured in decibels

Question 5

How much sound does it take to hear something?

Answer 5

• Faintest sound you can hear at 1 kHz is 20 micro-pascals = 0 decibels, and Standard Pressure Level
• Very small change in air pressure (atmospheric pressure and the water)

Question 6

What ranges to other animals hear?

Answer 6

• Mammals hearing depends on their body size e.g elephants are bigger so hear more lower frequencies and less higher frequencies, but rats hear higher frequencies more and better
• Mammals have a better range
• Some animals are extremely high frequency or have developed high frequency hearing to avoid bats like ultrasonic moths

Question 7

What is human detection of frequency

Answer 7

• Max sensitivity = 3 kHz, as you decrease frequency = lower sensitivity = cannot hear
• This Pa scale is sued as it is a log scale so compresses amount of numbers you end up with AND corresponds more with loudness

Question 8

What is the faintest and most intense sound you can bare?

Answer 8

• Faintest sound you hear = 0db
• Most intense sound you can bare = 120dB

Question 9

Why is the decibel scale not a scale of loudness?

Answer 9

• Loudness does not increase in proportion with either sound amplitude or intensity
• A 10-fold increase in decibels is 10db, but a hundred-fold increase is 20db
• A 10 db increase is about a doubling of loudness, rather than an increment
• Possible scales are decibels, logarithmic and linear, loudness is how auditory system chooses to interpret the physical stimulus

Question 10

What is magnitude estimation of loudness? (study)

Answer 10

• Give someone standard sound e.g worth 100
• Give something else and ask them to value that in comparison to the first value
• Different tones, same frequency, different order and average numbers were taken for the sounds perceived
• Can plot these numbers to create a loudness curve (even though subjective, most people get the same answer)

Question 11

What is an example of magnitude estimation?

Answer 11

• Asked participants to write down the sound change in reference to 100
• Results in a steady slope, regardless of population/sample

Question 12

Do sounds of the same pressure level but different frequencies have the same loudness?

Answer 12

• Comparing different tones, asking which ones matches the one with the same sound level, but the hz changes (match the 1000Hz to a 200Hz sound) = done at full volume first, and then with a much lower volume
• Gave rise to the equal loudness contours: taken tones of 1 kHz and compared them to other sound levels, every time one is the same, plot on the graph = apply weightings on sounds e.g a = low intensity, c = low intensity sounds the same as high intensities

Question 13

What are complex tones?

Answer 13

• Combined waveforms repeat themselves; they are periodic
• Waves can combine and you can hear sounds simultaneously, and then separated back out when reaches ear
• Used consistent ratio Hz sound good together e.g multiples of 200Hz form a harmonic series
• When you add these tones, you get a new sound wave that shows them added up, just looks more complicated.
• Characteristic feature of harmonic sounds are that they are periodic and repeat themselves: possible for a single object to vibrate in multiple frequencies at the same time

Question 14

What does a spectrogram show?

Answer 14

• Frequency against time
• Darker lines = sine waves show intensity of the harmonics
• Get fainter which is typical of most sounds
• When broken down, you can identify the pure tones and the structure of the sound change as time goes on