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An Introduction to Digital Audio

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Transcript

  • 1. SOUND EDITINGIntroduction to Sound Vilina Hutter, Instructor Digital Communications/49er ROP
  • 2. Sound Waves• Sound is caused by vibrations in the air – Guitar strings, vocal cords, speaker cones• Air molecules are pushed together, causing subtle air pressure changes – Ear drums interpret the pressure changes as sounds• Analog sound waves represent the shifts in air pressure
  • 3. Measuring Sound Waves
  • 4. Amplitude• Distance from the peak to the trough of the wave• The higher the amplitude, the louder the sound
  • 5. Frequency• Number of wave cycles per second• Measured in Hz• The higher the frequency, the higher the pitch
  • 6. Cycle/Phase• Cycle – Single sequence of pressure changes from zero to high to low, and then back to zero• Phase – Position in the cycle – Measured in degrees• Wavelength – Time it takes to complete one cycle
  • 7. Interaction of Sound Waves• In Phase – Waves that are perfectly in phase reinforce each other• Out of Phase – Waves that are perfectly out of phase cancel each other
  • 8. Interaction of Sound Waves• Waves that are out of phase in varying amounts combine to form a more complex wave
  • 9. Recording Sound Waves• Microphones convert pressure changes into voltage changes – High pressure becomes positive voltage – Low pressure becomes negative voltage• Voltage changes can be recorded as changes in magnetic strength on tape for analog recording• Digital recording is done by sampling the analog waveform
  • 10. Sampling• Each sample is a snapshot of the voltage value of the analog wave• The more often the sample is taken, the more accurate the digitization of the sound will be
  • 11. Sampling Rates
  • 12. Bit Depth• Size of each sample• Higher the bit depth, the better audio quality is possible
  • 13. Audio File Formats• Uncompressed – WAV (AIFF on the Mac) • Files can get very large • 5 MB per minute for a mono file at 44,100 sampling rate• Lossless compression – File formats that save space by not recording data for silence – FLAC, WavPack• Lossy compression – Complex algorithms that attempt to reproduce sound using less data – MP3, Ogg Vorbis, WMA (includes DRM), ra, AAC (I-Tunes)