3g Representing Sound

3g Representing Sound

  • Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.
  • Understand that sound waves are sampled to create the digital version of sound.
  • Describe the digital representation of sound in terms of:
    • sampling rate
    • sample resolution.
  • Calculate sound file sizes based on the sampling rate and the sample resolution.

3g Representing Sound

  • The sound wave is converted to an analogue voltage.
  • This analogue voltage is sampled.
  • The value of this voltage is converted to a binary value.
  • This binary value can then be processed and/or stored.
  • The reverse is done to output the sound from the computer. 

Sample Resolution

  • Also called bit depth
  • Image resolution affects the quality of an image allowing the image to capture more of the variation in light.
  • Audio sample resolution affects the quality of a sound allowing more variation in the sounds that can be recorded.

Sample Resolution

Sample Resolution

  • The higher the sample resolution the better the sound reproduction.
  • The higher the sample resolution the larger the sound file.
    • 2-bit sound allows four different sound values
    • 4-bit sound allows sixteen different sound values
    • 8-bit sound allows 256 different sound values
    • 16-bit sound allows 65,536 different sound values

Sample Rate

The number of times (per second) that a measurement is made is called the sample rate.

Sample Rate

Sample Rate

  • The higher the sample rate the higher quality of sound will be produced.
  • The higher the sample rate the larger the file size.
  • A high quality sound is usually sampled at 44.4 kHz (44,100 samples per second).
  • This is about twice the frequency a human can hear.

File Size

file size = sample rate × sample resolution × time

  • file size is in bits
  • sample rate is in Hz (samples per second)
  • time is in seconds

A sound sampled at 44 kHz for 30 seconds with a 16-bit sample resolution would need:

44,000 × 16 × 30 = 21,120,000 bits

21,120,000 bits = 2,640,000 bytes (2.64 MB)

Questions

  1. What is meant by the term sample resolution?
  2. What is the formula that relates file size, sampling rate, sampling resolution and length?
  3. Outline how an analogue sound wave can be converted into digital data and how quality is lost during the conversion.
  4. How does increasing the sample rate improve the quality of the sound?
  5. Explain why sound is not always sampled using settings that give the highest possible quality.
  6. A 200 second piece of audio is sampled using a sampling rate of 30 Hz and a sample resolution of 10 bits. What is the file size of the sampled audio?

Answers

  1. What is meant by the term sample resolution?

Sample resolution is the number of bits available for each sample.

  1. What is the formula that relates file size, sampling rate, sampling resolution and length?

File size = sampling rate × sample resolution × length

  1. Outline how an analogue sound wave can is converted into digital data and how quality is lost during the conversion.

The amplitude of the sound wave is measured at regular intervals to create a digital approximation of the sound wave. The amplitude between each sample is not recorded, causing a loss of quality.

Answers

  1. How does increasing the sample rate improve the quality of the sound?

A higher sampling rate means samples are taken more often, so less data is lost. This means the digital sound file will be closer to the original.

  1. Explain why sound is not always sampled using settings that give the highest possible quality.

Recording a higher quality digital version will increase the size of the file, which means more storage space will be needed and sending the file across a network will take longer.

Answers

File size = 30 × 10 × 200 = 60,000 bits

  1. A 200 second piece of audio is sampled using a sampling rate of 30 Hz and a sample resolution of 10 bits. What is the file size of the sampled audio?

3g Representing Sound

  • Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.
  • Understand that sound waves are sampled to create the digital version of sound.
  • Describe the digital representation of sound in terms of:
    • sampling rate
    • sample resolution.
  • Calculate sound file sizes based on the sampling rate and the sample resolution.
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