SLR 13 - Coding Sound & Music

Question 1

What are the two main categories of sound?

Answer 1

Analog and Digital.

Question 2

What is analog sound?

Answer 2

Natural sound waves occurring in a continuous waveform, e.g. human voice.

Question 3

How is analog signal defined?

Answer 3

A continuous signal representing physical measurements.

Question 4

How is analog sound data captured?

Answer 4

he sound wave is recorded onto a tape or other medium as a continuous waveform.

Question 5

How is analog sound represented?

Answer 5

Uses a continuous range of values to represent sound.

Question 6

How is analog sound captured?

Answer 6

Continuously varying quantities are measured and captured.

Question 7

What is digital sound?

Answer 7

A discrete digital format representing natural sound waves, e.g. DVD, MP3.

Question 8

How is digital signal defined?

Answer 8

Discrete time signals generated by digital modulation.

Question 9

How is digital sound data captured?

Answer 9

Analog waveforms are sampled at regular intervals, converted to numbers, and stored digitally.

Question 10

How is digital sound represented?

Answer 10

Uses discrete (discontinuous) values to represent sound.

Question 11

How is digital sound captured?

Answer 11

Quantities are counted, not measured.

Question 12

What does ADC stand for and what does it do?

Answer 12

Analog-to-Digital Converter – converts continuous natural sound waves into digital format.

Question 13

How do ADCs capture sound?

Answer 13

Used with analog sensors (e.g. microphones) to record amplitude at set intervals.

Question 14

What does DAC stand for and what does it do?

Answer 14

Digital-to-Analog Converter – converts digital audio signals into continuous natural sound waves.

Question 15

What are the two main factors that affect digital sound quality?

Answer 15

Sample Rate and Sample Resolution.

Question 16

What is sample rate?

Answer 16

How often the amplitude of a sound wave is recorded (samples per second), measured in Hertz (Hz).

Question 17

What is the typical sample rate for audio files?

Answer 17

44,100 Hz (samples per second).

Question 18

What is sample resolution?

Answer 18

The amount of detail in each sample – how many different amplitudes can be recorded, measured in bits.

Question 19

How many values can 16-bit sample resolution store?

Answer 19

65,536 values (2 bytes per sample).

Question 20

How many values can 24-bit sample resolution store?

Answer 20

98,304 amplitudes (3 bytes per sample).

Question 21

What is the Nyquist Theorem?

Answer 21

To accurately reproduce sound, the sampling rate must be at least twice the highest frequency of the original sound.

Question 22

How do you calculate sound file size?

Answer 22

Sample Rate × Duration (s) × Sample Resolution (bits)

Question 23

What is MIDI?

Answer 23

A technical standard that allows electronic music components and computers to communicate.

Question 24

What does a MIDI controller do?

Answer 24

Sends and receives event messages between devices.

Question 25

What data do MIDI messages contain?

Answer 25

Duration of note, pitch, bass, volume change, vibrato, tempo.

Question 26

Is a MIDI file a recording of audio?

Answer 26

No, it’s a list of instructions to synthesise sound.

Question 27

What is one benefit of MIDI files?

Answer 27

Takes up much less disk space than traditional digital recordings.

Question 28

What is compression?

Answer 28

The process of reducing file size as much as possible.

Question 29

Give four purposes of compression.

Answer 29

Reduce file size Reduce download times Reduce storage requirements Make better use of bandwidth

Question 30

What are the two types of compression?

Answer 30

Lossy and Lossless.

Question 31

What is lossy compression?

Answer 31

Removes data (e.g. reducing colours or simplifying pixels) which reduces quality slightly, often unnoticeable.

Question 32

When is lossy compression unsuitable?

Answer 32

When you can’t afford to lose any original data (e.g. medical imaging, legal files).

Question 33

What is lossless compression?

Answer 33

Compresses data without losing quality – allows full restoration of original file.

Question 34

What types of files is lossless compression ideal for?

Answer 34

Text documents and images with large areas of continuous colour (e.g. vector images).

Question 35

What are two types of lossless compression?

Answer 35

Dictionary Coding and Run-Length Encoding (RLE).

Question 36

What is Dictionary Coding used for?

Answer 36

Compressing text-based documents by storing data items with unique codes in a dictionary.

Question 37

What does a dictionary-coded file consist of?

Answer 37

The dictionary + a sequence of index references to recreate the original.

Question 38

What is Run-Length Encoding used for?

Answer 38

Compressing bitmap images with sequences of repeating pixels.

Question 39

How does Run-Length Encoding work?

Answer 39

Stores frequency/data pairs like: 22 0 (22 white pixels), 6 1 (6 black pixels), etc.

Question 40

What is encryption?

Answer 40

Encoding a message so it can only be read by the sender and intended recipient.

Question 41

What is a cipher?

Answer 41

An algorithm used to convert plaintext to ciphertext.

Question 42

What is the Caesar Cipher?

Answer 42

A substitution cipher where each letter is shifted by a fixed number of positions in the alphabet.

Question 43

What is needed to decrypt Caesar Cipher?

Answer 43

The key – the number of positions the letters were shifted.

Question 44

What is the Vernam Cipher?

Answer 44

A one-time pad cipher offering perfect security if: 1. The key is random 2. The key is as long or longer than the message 3. The key is used once and destroyed 4.The key is shared in person

Question 45

Why is the Caesar Cipher insecure?

Answer 45

It’s easy to crack using brute-force.

Question 46

Why is the Vernam Cipher secure?

Answer 46

It offers perfect security under strict conditions and cannot be cracked if used correctly.