02 - Analog vs. Digital Signals

Question 0

Analog Signals are continuous in _______ and in _______.

Answer 0

Time

Amplitude

Question 1

What are examples of an Analog Signal?

Answer 1

Speech Sounds

Musical Tone

Displacement of the middle ear bones

Question 2

What is a Digital Signal?

Answer 2

Discrete Time Signal

It only exists at discrete points. It is not continuous. There are empty moments in between.

Question 3

How does digitizing work? (2)

Answer 3

You need a representative sample.

You just need to know how accurate the digital representation needs to be.

Question 4

What does “digitization” literally mean?

Answer 4

To convert into numbers (digits) so that the information can be stored in numeric form

Question 5

What are the two main operations in digitization?

Answer 5

Sampling

Quantization

Question 6

Before sampling & quantization, the signal may be passed through a _______ and a ______.

Answer 6

Pre-Emphasis Filter

Pre-Sampling (Lowpass) Filter

Question 7

What does a Pre-Emphasis Filter do?

Answer 7

Boosts the higher frequencies

Question 8

What does a Pre-Sampling (Lowpass) Filter do?

Answer 8

Rejects the energy above the highest frequency of interest

Question 9

In the long term average of speech, is there more energy in the high frequencies or the low frequencies?

Answer 9

Low Frequencies

Question 10

Why do we need to boost the intensity of the high frequencies?

Answer 10

To make these levels to equal to that of the low frequencies

Question 11

What is Sampling?

Answer 11

Taking “samples” at given intervals

This makes the analog signal discrete in time

Question 12

What does a sampling rate of 10,000 Hz (10 kHz) mean?

Answer 12

That the analog signal has been sampled 10,000 times per second

Question 13

What is Nyquist’s Sampling Theorem?

Answer 13

That the number of samples taken must be TWICE the highest frequency of interest

Question 14

Why does the sampling rate need to be at least twice the rate of the highest frequency?

Answer 14

To avoid aliasing

Question 15

What is Aliasing?

Answer 15

When the higher frequencies aren’t sampled frequently enough, they appear as lower frequencies

Question 16

What are the two things that usually cause Aliasing?

Answer 16

Undersampling

No Lowpass Filter

Question 17

What are three ways to avoid Aliasing?

Answer 17

Determine the highest frequency of interest

Filter the energy above the highest frequency of interest

Sample the signal at at least twice the rate of the highest frequency of interest.

Question 18

What is a Quantum?

Answer 18

An increment of energy

Question 19

What is Quantization?

Answer 19

It converts the amplitude (energy level) of the samples

It makes the amplitude of the signal discrete

Question 20

What is the Quantization rate often called?

Answer 20

Resolution

Question 21

What is Quantization measured in?

Answer 21

Bits

Question 22

What are Bits?

Answer 22

Binary digits

Question 23

How many Bits does a 1-bit system have?

Answer 23

2 levels

Question 24

How many Bits does a 8-bit system have?

Answer 24

256 levels

(2⁸)

Question 25

How many Bits does a 16-bit system have?

Answer 25

65,536 levels

(2¹⁶)

Question 26

In Quantization, do you store the positive output, the negative output or both?

Answer 26

Positive

Question 27

What are the steps to Analog-to-Digital Conversion? (6)

Answer 27

Acoustic Signal

Pre-Emphasis Filter

Pre-Sampling (Lowpass) Filter

Sampler

Quantizer

Encoder

Question 28

What is Zipper Noise?

Answer 28

The noise that comes from square edging

Question 29

What is Square Edging?

Answer 29

How the sinwave becomes “choppy” due to the lesser quantization

Question 30

Do we listen to the digital signal?

Answer 30

No, it must be converted back into analog form

There is usually a final lowpass filter to smooth out the signal

Question 31

What are the steps to A/D and D/A conversion?

(6)

Answer 31

Acoustic Pressure Wave (Sound)

Microphone

Analog-to-Digital Conversion

Processing & Storage

Digital-to-Analog Conversion

Audio Output

Question 32

What kind of signal is this?

Answer 32

Analog

Question 33

What kind of signal is this?

Answer 33

Digital

Question 34

What is going on with the dotted line?

Answer 34

Aliasing