Data Representation - Sound

Data Representation - Sound

Analogue Sound Waves

• Sound is usually in analogue form (continuously changing data)…. but the computer needs to have this in digital form as a set of binary numbers.

• To store sound on a computer we need to convert the waveform into a numerical representation.

How is a sound wave converted to digital?

• To convert sound from analogue into a digital form the sound wave is sampled at set intervals and the height of the sound wave (amplitude) is recorded

Sampling

• Sampling takes a snapshot of the sound wave at that moment and then they are fitted together. 

Sample Rate

• The sample rate is the number of samples taken each second

• The higher the sample rate the better the sound quality, as the better represented the analogue sound wave is

• Usually measured in hertz

  (1 Hertz = 1 sample per second).

  
  

Sample Resolution

• The number of bits per sample

• Much as with colour, you can reduce the precision by using only 8 bits per sample instead of 24, for example.

Multiple Choice

What is sampling?

• Snapshot of the sound wave at that moment and then they are fitted together.

• The number of bits used to represent the sound

• The height of a sound wave

Multiple Choice

What is sample rate measured in?

• bits

• Hertz

• kbps

Multiple Choice

What is sample resolution?

• Snapshot of the sound wave at that moment

• The pitch of the sound

• The number of bits per sample

Converting a sound wave

• The device that converts an analogue signal into a digital representation is called an Analogue to digital converter(ADC)

  For sound waves, the analogue signal is converted as follows:

• ^{–Analogue sound is received by a microphone}

  ^{–This is converted to an electrical analogue signal}

  ^{–The signal amplitude(height of the wave) is measured at intervals (sampled)}

  ^{–The values are rounded to a level}

  ^{-The values are stored as a series of binary numbers}

Calculating file size

File size(in bits) = Sample rate * sample resolution * length(in seconds) 

The sound engineer is using a sampling rate of 1000 Hz and a sample resolution of 8 bits. What is the minimum file size of a 4 second recording?

1000 * 8 * 4

Multiple Choice

The sound engineer is using a sampling rate of 2000 Hz and a sample resolution of 4 bits. What is the minimum file size of a 10 second recording? Your answer should be given in bits.

• 80,000

• 10,000

• 8

• 800

Multiple Choice

The sound engineer is using a sampling rate of 4000 Hz and a sample resolution of 2 bits. What is the minimum file size of a 5 second recording? Your answer should be given in bytes.

• 5

• 5000

• 30,000

• 40,000

Multiple Choice

The sound engineer is using a sampling rate of 1000 Hz and a sample resolution of 8 bits. What is the minimum file size of a 10 second recording? Your answer should be given in KB.

• 2

• 160,000

• 10,000

• 10

Multiple Choice

The sound engineer is using a sampling rate of 1500 Hz and a sample resolution of 4 bits. What is the minimum file size of a 5 second recording? Your answer should be given in bits.

• 375

• 30,000

• 3

• 24,000

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