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Computer science A level > Sound representation - 92 - 95 > Flashcards

Sound representation - 92 - 95 Flashcards

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1
Q

What is analogue signal?

A

Natural sound waves, occurring in continuous wave form, for example, human voice

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2
Q

What is digital signal?

A

Discrete digital format for representing natural soundwaves

eg CDS AND DVDS

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3
Q

What are ADCs?

A

An analog to digital converter is any device, which can convert continuous natural soundwaves into a digital format

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4
Q

What are ADCs used for?

A

They measure and record the amplitude of the soundwave at set intervals
- They are used together with analog sensors

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5
Q

What is a DAC

A

A digital to analog converter is any device, which can convert a digital audio signal into a continuous natural soundwave

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6
Q

What affects the quality of the digitally converted soundwave?

A

The sampling rate and the sampling resolution

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7
Q

What is the sampling rate in simple terms?

A

The speed

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8
Q

What is the sampling resolution in simple terms?

A

The detail

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9
Q

What is sampling rate?

A
  • the frequency at which you record the amplitude of a sound wave
  • The more often you record a sample the smoother the playback will sound
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10
Q

What is sampling rate measured in?

A

Hertz

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11
Q

Advantages and disadvantages of increasing the sample rate

A

Advantage: the sample will be smoother and more detailed.

Disadvantage: the file will take up more space, as more information will need to be stored

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12
Q

what does the sampling resolution reprpesent

A

It represents how many different gradations of amplitude can be represented in a digital waveform

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13
Q

What is sample resolution measured in?

A

Bits

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14
Q

Advantages of increasing the sample resolution

A

It’s a more accurate representation of the wave and will sound better

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15
Q

What does Nyquist theorom state

A

to produce an accurate recording, you need to use a sampling rate, which is at least double that of the highest frequency in the original signal

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16
Q

What frequency can human ears hear?

A

20 Hz to 20,000 Hz

17
Q

proof of nyquist theorom

A

Humans can hear from 20 Hz to 20,000 Hz and modern digital audio samples at around 44,100 Hz

18
Q

How to calculate the size of the sample?

A

= Number of samples per second X Number of bits per sample X Length of sample in seconds

19
Q

What is MIDI?

A

It is a technical standard, which describes:

A protocol, a digital interface or a standard set of connectors

20
Q

Why is MIDI used

A

It allows for a wide range of electronic musical instruments or computers to communicate with each other

21
Q

How does MIDI work?

A
  • music represented as sequence of MIDI events messages
  • example of data contained in a message may be pitch, volume, velocity
22
Q

What do events messages specify?

A

Duration of note
Pitch
Volume change
Vibrato
Tempo synchronisation

23
Q

Summarise, MIDI

A
  • they are a list of instructions
  • which detail how to synthesise a sound
  • these sounds being pre recorded digital samples of real instruments
24
Q

Advantages of MIDI

A
  • more compact representation
  • it makes it easier to modify notes
  • simple method to compose algorithmically
  • no data lost about musical notes
  • musical score can be generated directly from a MIDI file
25
Q

how to convert analogue to discrete

A

measure and record the amplitude of a sound wave at given time intervals. the more frequently the samples are taken, the more accurately the sound will be represented

26
Q

how to increase the accuracy of a sound sample

A

increase audio bit depth

27
Q

process of analogue to digital (step by step)

A
  • ADC takes samples of the signal at regular intervals
  • the samples are quantised
  • each sample is assigned a binary value
28
Q

what is frequency determined by

A

the speed of oscillation/vibration of a wave

29
Q

what is the sample resolution

A

the number of bits per sample

30
Q

how long are MIDI messages

A
  • usually 2 to 3 bytes long
  • first byte is a status byte

Computer science A level (28 decks)

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