Digitization of Sound

Let us first analyse what a sound actually is:

• Sound is a continuous wave that travels through the air
• The wave is made up of pressure differences. Sound is detected by measuring the pressure level at a location.
• Sound waves have normal wave properties (reflection, refraction, diffraction, etc.).

A variety of sound sources:

Source

-- Generates Sound

• Air Pressure changes
• Electrical -- Loud Speaker
• Acoustic -- Direct Pressure Variations

The destination receives (sensed the sound wave pressure changes) and has to deal with accordingly:

Destination

-- Receives Sound

• Electrical -- Microphone produces electric signal
• Ears -- Responds to pressure hear sound

Sound is required input into a computer: it needs to sampled or digitised:

• Microphones, video cameras produce analog signals (continuous-valued voltages) as illustrated in Fig 6.1

  

  Continuous Analog Waveform

• To get audio or video into a computer, we have to digitize it (convert it into a stream of numbers) Need to convert Analog-to-Digital -- Specialised Hardware

• So, we have to understand discrete sampling (both time and voltage)

• Sampling - divide the horizontal axis (the time dimension) into discrete pieces. Uniform sampling is ubiquitous.

• Quantization - divide the vertical axis (signal strength) into pieces. Sometimes, a non-linear function is applied.
  • 8 bit quantization divides the vertical axis into 256 levels. 16 bit gives you 65536 levels.

Continuous Analog Waveform