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Analog to Digital Conversion of Sound

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					Analog to Digital Conversion of
            Sound

          Adam White
• Conversion Of Sound (ADC)

• Digital Audio Workstation(DAW)
           Basics of Signal Conversion
• Sender
• ADC
 - converts an input analog voltage to a digital number proportional to the magnitude of the voltage or
   current.
 - Binary, Grays Code, 2’s complement

• Data Manipulation
• DAC
• Receiver
             ADC Structures
• Binary – base 2
• Grays Code
• 2’s Complement
                     Sampling
• The process of going from continuous time to discrete
  time

• sample rate

• Higher the sample rate = better quality, more storage

• What is the best sampling rate?
           Nyquist’s Theorem
• the ADC's sampling rate must be at least twice
  the maximum bandwidth of the signal.
• The maximum bandwidth is called the Nyquist
  frequency.
• Aliasing
                Resolution
• the number of bits used to represent the
  analog input signal.
• Higher the resolution, the more accurately the
  signal is replicated.
• Higher resolution reduces the quantization
  error.
                 Resolution
• eight bits resolution means it can hold values
  from 0 to 255 (2^8 = 256)
  -Example: Phone Systems
• 16 bits resolution, this means it can hold
  values from 0 to 65,535 (2^16 = 65,536).
  - Example: Audio CD’s
• 24 bit resolution is used for high end audio
  applications.
           Quantization Error
• the difference between the actual analog
  input and the digital representation of that
  value
• Unavoidable
• Happens from rounding or truncation
• Is ok for phone systems
             Non-Linear Error
• physical imperfections
• Output deviates from the linear function of
  their input
• Can be prevented by testing
• Either best fit straight line or line between end
  points
                ADC Designs
•   Flash
•   Successive approximation
•   Ramp Counter
•   Wilkensons ADC
•   Integrated ADC
•   Delta Coded ADC
•   Pipeline ADC
•   Time Interleaved ADC
                      Flash
•   Efficient for small resolution
•   Fast
•   Only has 8 bits of resolution
•   Disadvantage – lots of comparators
               Ramp Counter
•   uses a counter
•   Records value when they are equal
•   Very Slow
•   Inefficent
        Successive Approximation
•   Based off of Binary Search
•   Throws out half the values each iteration
•   Better for larger resolution
•   Most popular
•   fast
•   C CODE
      Digital Audio Workstation
• DAW is the combination of a Mac or PC,
  software, and ADC.
• ADC in DAW acts as a sound card
• Usually external to computer. Often
  rackmountable
• High end sound cards, fast CPUs, lots of RAM,
  Large hard drives.
          Computer Based DAW
•   Separate Computer, Software, Hardware
•   More Prevalent today
•   Cheaper
•   Software controls the two hardware
    components and provides a user interface to
    allow for recording and editing.
             Integrated DAW
• combines all of the necessary components
  such as computing power, software, analog to
  digital conversion, and a gui all in the same
  unit.
• More popular throughout the 1980’s and
  1990’s
• As computing power increased and costs
  decreased, popularity of integrated systems
  dropped.
                      DAW
• allows the software to act like a mixer
  – Volume control
  – Panning
  – EQ
  – Effects
  – cut, copy, paste
  – Splicing tracks
  – Multi-track Recording
  – “forcast” tracks
                   History
• Created by Bob Ingebretsen and JimYoungber
• 1970
• First available to consumers in 1987 by
  digidesign
• Digidesign was available to Macintosh users
• Originally called Sound Tools – later chaged to
  ProTools.
• First Windows DAW introduced by
  Soundscape Digital Technology (year)
                Pro Tools
• Mac or Windows
• More popular among Mac
• Developed and designed by DigiDesign
• Must be used with a DigiDesign ADC
• M-powered can be used with M-audio
  interface
• First version sold for $6,000
• Sold now for $495 to $1995
• “Industry Standard”
                 Cubebase
•   Created by Steinberg
•   Windows or mac
•   More popular for windows
•   First released in 1989
•   $499
             Open Source
• Audacity
• DEMO

				
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