Digital Audio

1
Digital Audio

• An introduction to Digital Audio

2
The Range of Human Hearing

• 20hz-20 000hz(20kHz)
• most sensitive to sounds around the 1kHz to 4kHz
  normal conversation
• dogs 35 kHz ultrasounds
• ultrasounds also used by doctors
• Sounds below 20 Hz are called infra sound
  earthquakes

3
Dynamic range

• measured in decibels (dB)
• measured logarithmically
• 140dB aeroplane
• 120dB threshold of pain
• 115dB loud rock concert
• 100dB chainsaw
• 90dB lawn mower
• 60dB normal conversation
• 30dB whisper
• 0dB audible sound third by the human ear

4
Understanding Digital Audio

• around for over a decade
• sampler keyboards or samplers
• first musical uses for digital audio technology
• very expensive technology

5
Digital Audio Recording

• 2 main differences between analog and digital
  audio
• how sound is recorded
• how it is playback
• analog recorded by transferring electrical
  energy onto a magnetic medium
• digital sound-recorded by means of a process
  called sampling.
• main hardware analog to digital converter

6
Sampling

• converts electrical energy to the binary code of
  1s and 0s, also called bits
• audio sample is similar to a frame of motion
  picture
• samples are playback at high speed
• the sample create a draft of the waveform, which
  was caused by the vibration and harmonics of the
  sound
• saved onto the hard disk
• When playedback this sound is sent to digital to
  analog converter

7
Factors affecting Sampling

• 2 main factors affect the quality of the digital
  recording
• sample rate - how often the waveform is measured
  every second
• 11k,22k,44.1k,48k
• Nyquist theorem
• sample resolution - determines the decision of
  those measurements

8
How audio is digitized

• digitizing is another way of describing sample
• analog data-converted to electrical
  current-analog to digital converter
• sampling resolution determines how accurately the
  sample were described original wave(8 bit 256
  levels of acoustic energy,16 bit 65,000 levels)
• when playedback digital sound is sent through a
  digital to analog converter which produces and
  analog waveform
• a filter smooths out the digital sound wave

9
Analog sound vs. Digital Audio

• Records - Compact disks
• Cassettes - Mini Disc and Digital Compact
  Cassettes
• Reel-to-Reel tape - Digital Audio Tape(DAT)
• Television - High Definition Television(HDTV)

10
How PCs use Digital Audio

• formats of the sound file - SND,WAV,AIFF
• not every personal computer can playback DIGITAL
  SOUND FILES - eg. AIFF
• main ingredient -audiochip that provides for DSP
• DSP chip takes the pressure of the computers
  brain(CPU)

11
How Computers play the Digital Audio

• 1. when you trigger a digital sound from your
  computer-software translates your command into a
  binary code and sends the sound to the computers
  audio system software
• 2. Audio system software sends the file to an
  audio output chip on the sound card-the order
  chip converts the digital to analog signal
• 3. The audio output chip is sends the low level
  analog signal to an internal amplify which in
  turn strengthens the signal and sends this to
  internal speakers or or RCA port for further
  amplification.

12
Digital Audio Editing

• revolutionised the way we edit music - like word
  processors
• instead of being accurately a few dozen the
  seconds we can edit 16 bit CD quality digital
  sound to 1/44100 of a second
• equivalent to changing not only the photograph
  but each individual dot

13
Project

• Read Module 10 Experiencing Music technology
  Williams and Webster
• Record the first minute of any symphony in the
  following formats
• 11khz,22kz and 44,1khz both stereo and mono
• Compare and contrast these files in terms of
  size,quality of audio, fidelity,