Introduction

Question 1

What does a system do?

Answer 1

Perform an operation or transformation of a signal or waveform

Question 2

What does a x2 amplifier do?

Answer 2

Increases the amplitude by two times

Question 3

What are the two major types of waveforms?

Answer 3

Periodic and aperiodic

Question 4

What are periodic waveforms?

Answer 4

-Basic unit that repeats in time
-This gives it periodicity
-Typically have strong pitch

Question 5

What are the two types of periodic waveforms and how do they differ?

Answer 5

Simple and complex
Complex periodic waveforms are constructed from multiple sinusoids and can be constructed into multiple sinusoids

Question 6

What is a sinusoid?

Answer 6

A sinusoid is just a different word for a sine wave. It looks like a continuous wave

Question 7

What are the characteristics of aperiodic waveforms? What are the two types?

Answer 7

-Do not repeat
-Can be transient (like a click or a clap) or continuous

Question 8

What is sound?

Answer 8

The oscillation of air pressure

Question 9

What happens to air molecules at high pressure vs low pressure?

Answer 9

High pressure- air molecules bunched up
Low pressure- air molecules spread out

Question 10

How do air molecules travel through space?

Answer 10

As sound waves

Question 11

How is sound measured?

Answer 11

As the pressure changes over time at one point in space

Question 12

What are the essential characteristics of sinusoids?

Answer 12

-Have a unique shape
-Are a periodic wave (basic cycle which repeats over and over)
-Can be constructed from uniform circular motion

Question 13

What are the three ways that sinusoids can differ?

Answer 13

1. Frequency
2. Amplitude
3. Phase

Question 14

What is phase?

Answer 14

Where a sinusoidal wave starts relative to some arbitrary time

Question 15

What is phase measured in?

Answer 15

Cycles or degrees (radians)

Question 16

What is a radian?

Answer 16

If you were to wrap the length of the radius over a circle, the radian is the angle formed at the centre of that circle

Question 17

How many radians is 360 ̊, 180 ̊ and 90 ̊?

Answer 17

360 ̊ = 2π rads
180 ̊ = π rads
90 ̊ = π/2 rads

Question 18

What is the frequency?

Answer 18

A measure of how fast the sinusoid is repeating

Question 19

What is the period?

Answer 19

The time taken to complete one cycle of the wave

Question 20

What is the mathematical relationship between frequency and period?

Answer 20

Frequency= 1/ period
Period= 1/ Frequency

Question 21

How does an increase in frequency (and consequent decrease in period) affect pitch?

Answer 21

-Subjective pitch increases
-As the sine wave gets faster in frequency the pitch gets higher

Question 22

What is the amplitude?

Answer 22

-Specifies how loud a sound is
-Increases in amplitude lead to increases in perceived loudness

Question 23

What are simple measures of amplitude?

Answer 23

1. Height of the peak
2. Peak to peak amplitude

Question 24

What is the problem with peak measures?

Answer 24

They don’t accurately reflect the energy in a waveform

Question 25

What is the root-mean-square (rms)?

Answer 25

-A measure of the energy, applicable to all waveforms
-A sinusoid and its square

Question 26

How is the root-mean-square calculated?

Answer 26

-Square all the values of the wave
-Take the average area under the curve
-Take the square root

Question 27

What is meant by dB SPL?

Answer 27

-Decibel of sound pressure level
-The intensity of a sound
-The smallest audible sound humans can generally hear is 0 dB SPL (hearing threshold)

Question 28

How is dB SPL calculated?

Answer 28

-Pressure of a wave is that we measure is divided by 20μPa

Question 29

Why is 20μPa used in the dB SPL calculation?

Answer 29

-20μPa is the standard reference pressure
-It is approximately equal to human threshold

Question 30

What is the point of a log scale?

Answer 30

Log scales convert exponential changes into linear ones

Question 31

Are pressure and dB SPL linear or logarithmic?

Answer 31

-Pressure (in pascals) is a linear measure
-dB SPL is a logarithmic measure

Question 32

Why is a logarithmic unit (dB) used to measure the intensity of a sound?

Answer 32

-Our perception of changes in sound amplitude is based on ratios/ proportions which is closer to a logarithmic scale
-For example, there is an obviously noticable change between a 1 kHz sinusoid of 50μPa and 100μPa
-However adding one 1Pa to a 50μPa sound it is only 1.000005 Pa which is an indistinguishable change

Question 33

What is the minimum change in dB needed to distinguish a difference in the loudness of a sound?

Answer 33

1 dB

Question 34

Equal steps on a dB scale correspond to….

Answer 34

Equal ratios on the linear scale