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AUDI 514 - Hearing Science > Lecture 1 > Flashcards

Lecture 1 Flashcards

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1
Q

What is the One-Mass model?

A

Like mass and spring, in the trachea. Muscles create resonance; pressure built up due to narrowing in the trachea. Waves create a fluctuating high to low pressure.

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2
Q

In One-Mass model, what does condensation and rarefaction mean?

A

High pressure area - condensation (narrowing at trachea)

Rarefaction - less condensation (low pressure area)

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3
Q

What are the components of sound production?

A

Transduces electrical energy into mechanical energy - pressure wave set up with motion, sinuisoidal wave created.
Increase in volume = decrease in pressure.

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4
Q

What is sound?

In terms of vibration,

A

Vibration - movement of object from one point to another point in space, and usually back to the first point. Must produce a sound wave in a medium - leads to hearing (air)

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5
Q

What is sound? In terms of auditory sensation

A

Auditory Sensation - produced by alteration in pressure, particle displacement or particle velocity which is propagated in an elastic medium through the ear

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6
Q

What is the mass-spring system?

A

Molecules in the air, elastic collisions can change how these move in space
Molecule bounce through the spring system.
Transfer of energy in springs, they compress and expand from pushing of mass.
Pressure waves transferred by molecules

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7
Q

What is simple harmonic motion?

A

When an object, displaced from its equilibrium position, is acted on by a force proportional to the displacement, object will undergo a periodic motion, which, in the absence of friction is….
Ex. Springs and masses that pull and let go - move in sinusoidal fashion

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8
Q

What force is periodic motion controlled by?

A

Resistance (R): forces associated with friction “waste” energy and eventually causes the motion to stop. Turns energy of vibrating motion into heat

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9
Q

What are another 3 forces periodic motion is controlled by?

A

Inertia: Is a property of matter. Once moving, the body will “want” to continue moving; if at rest the body will stay at rest unless acted upon by some force.

Stiffness = 1/elasticity; force that depends on how much displacement there is.

F = -kx (Hooke’s Law) (k = spring constant, x = displacement) - restoring force of spring when mass is displaced.

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10
Q

Free Vibration of a Simple Mass and Spring System
What happens to spring at rest?
What happens at t=0?
What happens at t>0?

A

Rest: spring not stretched or compressed, applies no force.
t=0: free vibration, no external forces applied after t>0. (F = ma)
Oscillations will continue with same acceleration as time passes, eventually traces sinusoid. (Natural/Resonant frequency = f = √( k / m ))

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11
Q

What are the three forces that control periodic (vibratory) motion?

A

Resistance (R)
Inertia
Stiffness

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12
Q

In the oscillation of 3 masses, which one will have the highest frequency? Why?

A

Smallest mass =highest frequency.
Frequency of vibration proportional to √ of stiffness or restoring force and inversely proportional to √ of mass.
Mass x4 = 1/2 frequency; stiffness x4 = 2x frequency

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13
Q

What is a sinusoid? Why should we care?

A

Mathematical equation describing a curve with the form of a sine wave. Sum of sinusoids is a combination of waves.
Describe the responses of many simple physical systems (mechanical and acoustical ones relevant to speech and hearing).
More complex signals can be represented by sum of many sinusoids where amplitude, frequency and starting phase define net result.

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14
Q

What is a sine wave?

A

Rotating phase in 360 degrees; oscillation in a circular fashion. How fast sine wave spins = phase.
Sound waves = sinusoids.

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15
Q

Sinusoids: What is frequency?

A

Number of complete cycles that occur in one second. Commonly used unit is Hz
Reciprocally related to period: f=1/P

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16
Q

Sinusoids: What is period?

A

Amount of time it takes to complete one full cycle (seconds)

P=1/f

17
Q

What is starting phase?

A

Point in the displacement cycle the object begins to vibrate. Can have difference degrees as start phase

18
Q

What is instantaneous phase?

A

Start phase both equal 0 degrees but phase at different points in time (instantaneous phase) differs between two waves
At certain time, where they intersect.
Look at which degree wave is sitting on.

19
Q

What is amplitude?
Instantaneous amplitude?
Peak amplitude?

A

Measure of displacement. Measure of displacement of sine wave that varies with time - instantaneous amplitude.
Measure of displacement of a sine wave that doesn’t vary with time - peak amplitude, and RMS (energy in sinusoid)

20
Q

What are the downfalls of peak amplitude?

A

Works well for sinusoids, insufficient for describing amplitudes of different frequency sinusoids over a specific interval; amplitudes of non-sinusoidal/complex waveforms

21
Q

What is an FFT? Why is it important?

A

Samples signal over period of time and divides it into its frequency components. Components are single sinusoid oscillations at distinct frequencies each with own amplitude and phase.

22
Q

What is Fourier’s Analysis?

A

Of a complex waveform expressed as a series of sinusoidal functions, the frequencies of which form a harmonic series. Difference shapes of time waveforms can be created by varying the relative amplitudes of the summed sinusoids.

23
Q

What are two ways to represent a sound?

A

Time-domain and frequency-domain amplitude spectrum

24
Q

How is sound a change of pressure in air?

4 Reasons

A

Waveform of any sound shows how the pressure changes over time
Eardrum moves in response to changes in pressure
Any waveform shape can be produced by adding together sine wave of appropriate frequencies, amplitudes and phases
Amplitudes of sine waves give the amplitude spectrum of the sound. For a sine wave this is a single point at the frequency of the sine wave.

25
Q

How is phase measured? What does a shift in phase mean?

A

Phase measured in degrees or radians, indicates relative time of a wave. Two waves can have identical frequencies and amplitudes but differ in phase.
Shift in phase for a sine wave is equivalent to shifting in time.

26
Q

What happens when you add sounds of different frequencies together?

A

If all component frequencies are an integer multiple of the first one, this is a harmonic complex tone

27
Q

What is complex sound?

A

Sound which has more that one sine-wave frequency component

28
Q

What is periodic sound?

A

One which repeats itself at regular intervals (sine wave)

29
Q

What is fundamental frequency?

A

Lowest frequency of a periodic waveform. Each harmonic component is a sine wave that has a frequency that is an integer multiple of the fundamental.

30
Q

What are the effects of duration?
Continuous waveform
Wave on/off
Instantaneous on/off

A

Continuous waveform: distinct peak, continuous pure tone, single line at frequency of tone. (Smaller bandwidth)
On/Off: pure tone with short duration - larger bandwidth, wider spectral region with many peaks
Instantaneous: contains all frequency components with equal levels (flat line)

INCREASE DURATION = DECREASE BANDWIDTH

31
Q

Duration and Bandwidth: what happens?

A

Add energy to make it flat, add side lobes to destruct - make null frequency in opposite phase. Lobes are destructive frequencies.

32
Q

Click Stimuli: What are components and what do they look like?

A

The shorter the stimulus, the broader the spectrum.
F0 is determined by click repetition rate (1/T). Amplitude of each harmonic is determined by click duration (D).
Line spectra - not continuous.

33
Q

What happens if you add tones of different frequencies together?

A

If small difference, beating results.
At regular intervals, the peaks in fine structure of tones combine, producing maxima in envelope. Between envelope maxima, there is time when peak in structure of one waveform matches trough in other waveform. Cancellation produces minimum in the envelope - hear as beats

34
Q

What is amplitude modulation?

A

Sound created when you vary volume. Refers to variations in the envelope of the sound.
Original tone - carrier, slow up/down fluctuations - modulator.
Produced by multiplying the carrier waveform with the modulator waveform.
3 Components:
Fc = carrier frequency
Fc + Fm = modulator frequency
Fc - Fm

35
Q

What is frequency modulation?

A

Refers to variations in the frequency of a sound.
Carrier - original waveform
Modulator - waveform that describes variation in frequency over time.
Carrier sinusoidally frequency modulated, frequency will vary up and down in pattern of sine wave.
Will vary from Fc - m to Fc + m every 1/Fm sec

AUDI 514 - Hearing Science (15 decks)

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