Representing Sound

Representing Sound

Specification

Bit Patterns, Images, Sound and Other Data

• Describe how bit patterns may represent other forms of data, including graphics and sound.

Analogue and Digital

• Understand the difference between analogue and digital:
  • data
  • signals

Analogue/Digital Conversion

• Describe the principles of operation of:
  • an analogue to digital converter (ADC)
  • a digital to analogue converter (DAC)
• Know that ADCs are used with analogue sensors.
• Know that the most common use for a DAC is to convert a digital audio signal to an analogue signal.

Digital Representation of Sound

• Describe the digital representation of sound in terms of:
  • sample resolution
  • sampling rate and the Nyquist theorem.
• Calculate sound sample sizes in bytes.

Musical Instrument Digital Interface (MIDI)

• Describe the purpose of MIDI and the use of event messages in MIDI.
• Describe the advantages of using MIDI files for representing music.

Bit Patterns, Images, Sound and Other Data

So farm we've only seen bit patterns used to represent numbers. However, computers also use bit patterns to represent all other forms of data, including graphics and sound.

Analogue and Digital

Analogue data is continuous, there are no limits to the values that the data can take. In contrast, digital data is discrete, meaning that it can only take particular values.

Analogue and digital signals vary in a similar way. An analogue signal can take any values and can change as frequently as required whereas a digital signal must always take one of a specified range of values and can only change value at specified intervals.

The trace of a digital signal's value against time is characterised by sharp edges and vertical drops as the signal changes value. While analogue signals tend to be smooth curves, they can sometimes feature sharp peaks. 

Analogue/Digital Conversion

Digital to Analogue Conversion

When converting from digital to analogue, a device called a digital to analogue converter (or DAC for short) is used. The device reads a bit pattern representing an analogue signal and outputs an alternating, analogue, electrical current…