Multimedia Elements: Sound Audio

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Multimedia Elements Sound / Audio
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Objectives

• Describe the sound and audio elements that make
  up multimedia
• Specify the tradeoffs involved in using these
  elements
• Specify the advantages and disadvantages of using
  these elements
• Describe the programs used with these elements

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Sound

• Comprises the spoken word, voices, music and even
  noise.
• Based on two thing
• Energy
• Transport medium

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Sound

• Volume height of peak
• Frequency distance between peaks, measured in
  hertz (Hz)

Frequency
Volume
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Sound

• There are two characteristic of sound
• Amplitude the power or intensity of the sound.
  The louder the sound, the larger the amplitude.
• Frequency is the rate at which sound is
  measured. It is measured in cycles per second or
  hertz (Hz). The higher the frequency, the clearer
  and sharper the sound

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Sampling

• A digital representation of a portion of the
  sound is made every fraction of a second.
• Sample rate how often is the digital
  representation made?
• Sample size how large is each digital
  representation?

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Digitizing Sound

• Digitizing sound means capturing the sound
  amplitude at a specific frequency
• Three characteristic for recording sound
• Frequency rate
• Amplitude measurement
• Sound channel (mono or stereo)

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Digitizing Sound

• For multimedia computers, standard frequency
  rates includes
• 11.025 KHz
• 22.5 KHz
• 44.1 KHz

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Digitizing Sound

• Amplitude measurement is based on 8 bits and 16
  bits
• 8 bits allows for 256 levels, which is adequate
  for many type of sound.
• 16 bits allows for 65,536 levels of sound, which
  provides a much finer level of precision.

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Calculating Audio Data Size

• Using the three characteristics of audio for
  calculating audio file sizes, amplitude, sound
  channel, and frequency rates.
• Variables
• c number of channels (mono 1, stereo 2)
• s sampling rate in Hertz (cycle per second)
• t time (seconds)
• b bytes (1 for 8 bits, 2 for 16 bits)
• File size c s t b

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Calculating Audio Data Size

• For example, calculate the file size for 1
  minute, 44KHz, 16 bit, stereo sound.
• c 2 (two channels stereo)
• s 44,100 (Hz frequency)
• t 60 (time)
• b 2 (bytes, 16 bit capture)
• File size 2 44100 60 2 10,584,000 bytes

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Digital Audio

• Note that
• Higher frequency, stereo, and 16 bits are used
  for best quality of capture
• Lower frequency, mono, and 8 bits are acceptable
  for voice quality (talking voice, not singing)
• Using mid-range frequencies (22.025 KHz) with 8
  and 16 bit, offer options for file sizes and
  quality.

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Digital Audio System

• Digital audio systems for multimedia computers
  are based on special circuitry that interfaces
  the computer to external audio components such as
  microphones, audio players and recorders, and
  speakers
• The circuitry for digital audio systems are often
  found in special purpose add-on hardware or as
  integrated parts of the computer system.

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Digital Audio System

• Digital audio circuitry is responsible for
• Converting the audio signal from a microphone or
  other audio source into a digital signal via a
  special component called an analog to digital
  converter
• Transferring the digital data to the computers
  storage media
• Converting a digital data from storage into an
  analog audio signal via a digital to analog
  converter and, if necessary, amplify it for
  playback using speakers.

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Digital Audio System
Digital Audio Circuitry
Audio Player or Recorder
Analog to Digital Converter
Line in
Data Storage Digital Audio File
Microphone
Microphone
Digital to Analog Converter
Line out
Audio Speakers
Amplifier
Speakers
Digital audio hardware configuration showing
input, output and storage
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Digital Audio Software Support

• The digital audio circuitry is managed by
  software that provides a number of user and
  software support functions
• Playback translate the audio data into sound.
• Record capture audio data from an external
  analog source
• Stop halt playback
• Fast forward move to a later point in the data
  stream
• Reverse move to a prior point in the data stream
• Rewind move to the beginning of the data stream.

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Sound Card

• Used to digitize sound
• Accepts analog input from audio source
• Samples according to specified sample rate and
  sample size
• Produces digital representation of the audio
  signal

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Sound Editing Programs

• Digital representations can be easily manipulated
• Cut and paste
• Sound effects (echo, fade-in, fade-out, etc.)

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Editing Digital Audio

• One of the advantages of digital audio system is
  random access, based on the ability of computer
  storage devices to jump to any point in the
  storage medium and access data.

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Editing Digital Audio

• Digital audio editing consists of capturing and
  modifying an audio data file. Most audio editing
  software include a number of editing techniques
• Trimming removing dead spot from the beginning
  and end of a digital recording
• Splicing and assembly linking separate audio
  segments together, usually from different files
• Volume adjustments increasing the loudness of
  softening the sound level also used to soften or
  eliminate distortion

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Editing Digital Audio

• Format conversion changing the file format to
  move audio between computer systems or changing
  data formatting
• Resampling or downsampling changing by reducing
  the frequency or number of bits used for
  recording.
• Fade-in and fade-out increasing and decreasing
  the volume within a segment of the audio data
• Equalization used to clean up noise by reducing
  spikes or levels within the audio data stream
• Time stretching slowing down or speeding up the
  sound by removing or adding filler data to the
  signal

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Editing Digital Audio

• Digital signal processing digitally adding
  sound effects such as reverberation, echo,
  inserting silence or sound level and other
  effects.
• Reversing sounds reversing the data stream to
  play the sound backwards.

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Editing Digital Audio

• At a minimum, simple audio capture/editing
  software allows
• Recording of digital audio segments
• Trimming of digital clips
• Splicing of clips, usually by adding a segment to
  the beginning or end of the original segment
• Volume adjustment of the entire segment
• Reversing the entire segment
• Copy, cut, paste and delete segment of digital
  audio

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Sound Control

• Mutlimedia computer usually have software that
  acts as a control for the computers sound
  playback and recording.
• This software includes
• Selection of component (mic, speakers, line-in,
  line-out)
• Volume level, both monaural and stereo
• Recording input level
• Bass and trebel controls

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Audio Quality

• The quality of the original audio depends on a
  number of factors
• The quality of the original audio source
• The quality of the capture device and supporting
  hardware
• The characteristics used for capture (frequency,
  data rate, and number of channels).
• The capability of the playback environment

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Sample Rate

• Common sample rates
• 11.025 kHz
• 22.05 kHz
• 44.1 kHz
• The more samples, the more accurately the sound
  is represented
• The more samples, the larger the file size

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MIDI

• Musical Instrument Digital Interface
• MIDI files
• Coded events (such as note pitch and duration)
• Series of instructions that can be followed by
  any MIDI-capable musical instrument

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MIDI Compared to Digital Audio

• Advantages
• More precise editing is possible
• File sizes are much smaller
• Disadvantages
• Only MIDI-capable instruments can send MIDI
  instructions
• Only MIDI-compatible playback devices can be used