Digital Audio

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Digital Audio
Recording Audio
Instructor Todd M. Abramovitz, Assistant
Professor
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Acoustics

• Acoustics is
• The scientific Study of audio
• Frequency
• Decibels
• Hardware
• Software
• Harmonics
• Acoustic Signature The acoustic signature of a
  system is data containing all of the sound
  characteristics of a system. This includes such
  things as reverb time, frequency response and
  other timbral qualities. Impulse files used by
  Acoustic Mirror can be thought of as acoustic
  signatures.

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Resolution

• Audio Resolution Bit Depth
• The number of sounds uses the same bit resolution
  as graphics.
• A bit is either on or off. (value 2)
• 8 bits or 28 256 sounds
• 16 bits or 216 Thousands of sounds
• 24 bits or 224 Millions of sounds
• Measuring size

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Frequency

• Frequency Wave Rate (cycles per second) or wave
  length (Hz)
• frequency   Pronunciation Key  (fr kw n-s )n.
  pl. frequencies
• The property or condition of occurring at
  frequent intervals.
• Mathematics Physics. The number of times a
  specified periodic phenomenon occurs within a
  specified interval, as
• The number of repetitions of a complete sequence
  of values of a periodic function per unit
  variation of an independent variable.
• The number of complete cycles of a periodic
  process occurring per unit time.
• The number of repetitions per unit time of a
  complete waveform, as of an electric current.
• www.dictionary.com

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Frequency

• From hearing to feeling
• Human Ear Dynamic Range
• 50 Hz to 20,000 Hz
• 50 Hz -- a low, deep, distant background hum
• 20,000 Hz -- high pitched like a drill or highest
  notes of a soprano
• Below 50Hz is usually felt like a deep bass when
  amplified can make a human sick.
• Above 18,000Hz is not heard by the human ear no
  matter how amplified, allthough a dog can hear it.

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Decibels

• Decibels Amplification of wave or wave height.
• decibel   Pronunciation Key  (d s -b l, -b l
  )n. Abbr. dB
• A unit used to express relative difference in
  power or intensity, usually between two acoustic
  or electric signals, equal to ten times the
  common logarithm of the ratio of the two levels.
• a logarithmic unit of sound intensity 10 times
  the logarithm of the ratio of the sound intensity
  to some reference intensity syn dB, db
• www.dictionary.com

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Decibels

• The pressure of sound
• 0 dB - Threshold of hearing
• 10 dB - Rustling leaves
• 20 dB - Whisper
• 40-60 dB - Conversation
• 90 dB - Jack Hammer
• 110 dB - Rock concert
• 130 dB - Threshold of pain
• 160 dB - Instant perforation of eardrum

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Putting it together

• Telephone Quality
• Web Quality
• Radio Quality
• mono
• stereo
• CD Quality
• Dolby Quality
• HiFi Quality
• Production Quality

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File Size

• Pulse Code Modulation (PCM) A method by which
  an audio signal is represented as digital data.

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Noting the Difference

• Record Audio Complete the following chart.

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Noting the Difference

• Record Audio Complete the following chart.

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Sound Forge

• Starting a new file
• Audio Settings Windows XP.
• handout
• Audio settings Sound Forge 5.
• Start a new Sound Forge file.
• Set the recording for CD quality.
• Record 1minute with the microphone.
• Save the file using PCM/WAV format.
• Listen and Note the quality auditory and
  technically
• Using Sound Forge resample the audio file see
  chart noting the changing effect of the resample.

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Vocabulary

• Key Vocabulary for this section.
• Acoustics
• Decibel
• Frequency
• Wave
• PCM
• Resample
• Insertion Point
• Reactive Preview
• Sample
• Trim/Crop
• Undo/Redo History

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Conclusion

• Quality VS Size.