Sound & Computers by d56FZ3E

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									Adam Diel
   In 1981 IBM PC 150 introduced the first PC
    Speaker.
       Each game had to write support for it (sound cards
        were impractical during this time)
       Could only play one square wave at a time
   It wasn’t until 1988 the first sound card came to
    the market.
       Introduced by Creative Labs
       Created ability to have multiple channels playing
   All sound that the human ear hears
    is an analog signal
     A continuous electrical signal


   In order for the computer to do
    anything with it, it must be
    digitized.
     Converted to 1’s and 0’s
   DAC = Digital to Analog Converter
   ADC = Analog to Digital Converter
   The soundcard of a computer (integrated into
    the motherboard or an extra peripheral) will be
    both the DAC and ADC for the computer.
       DAC for input (using a microphone for skype)
       ADC for output (playing music on speakers)
   Sample Rate = The number of times
    your audio is measured per second.
     The standard for CDs is 44.1 kHz
      (44,100 slices/sec)
     The higher the sample rate the
      better the quality
Audio is sampled at every
   dash on the graph
   Bit Depth = Also known as the resolution of the
    file, this is how many bits you have to capture
    audio
       Think of it as a series of levels that audio can be
        sliced into at any given moment in time.
   Bit Rate = How much data per second is
    required to transmit the file.
       How big the file actually is.
       Usually used to measure quality in lossy formats.
Each Line Represents One
       Bit of Data
   Dynamic Range = Largest amplitude the sound
    file can contain without distortion.
       Think of this as the highest/lowest level on the
        sound wave from the bit depth.
Dynamic Range
   Noise = Unwanted noise on an audio track
       Also known as white noise
       Could be a number of things, bad shielding, poor
        DAC or ADC, power supply, etc.




        Without Noise               With Noise
   Distortion = alteration of the original shape (or
    other characteristic) of a sound wave.
       This could be done on purpose
         Electric Guitar Player’s have distortion pedals
         Special effects like echo’s
   Clipping = A form of distortion that occurs
    when an amplifier/speaker is overdriven




                                            Clipping
          WahWah
   General misconception of “if it’s good enough
    for CD it’s good enough for me.”
       Much of the audio quality is lost. People don’t
        realize what they are missing.




        Low               Medium              High
   Can be divided up into three categories
       Uncompressed
       LossLess
       Lossy formats
   These are WAV (windows) or AIFF (mac) files
    that are considered ‘lossless’ files.
       Roughly 10MB per minute
   The initial recording of sound is usually done
    in this format before being compressed down.
   CDs (not MP3 CDs) are uncompressed sound
    files.
       It’s why you can only get 80 minutes vs 700 MB
        (roughly 700 minutes of mp3)
   FLAC (Free Lossless Audio Codec), Apple
    Lossless Audio Codec, and Monkey’s Audio
    codec are all examples of this.
       Roughly 5MB/Minute
   These are specifically designed for Audio files
    and lets you convert back to uncompressed
    formats.
   These formats are ideal for the audiophile with
    great sound setup.
   The most common formats used today, Mp3,
    AAC, & WMA (Windows Media Audio)
       Roughly 1 MB/Minute.
   Quality of these files can be referenced by the
    bit rate of the file. The higher the bit rate, the
    more that was preserved in the compression.
       Also means a larger file size.
   The reason why Lossy formats are so popular
    is the amount of space uncompressed sound
    files can take up versus compressed files.

   Back when storage wasn’t as cheap this was a
    huge benefit to home users.
   Has four basic components
       Analog-to-digital converter
       Digital-to-analog converter
       ISA, PCI, PCIe interface to connect to the
        motherboard
         Unless integrated
       Input/Output Connections for microphones,
        speakers, etc.
   The ADC will translate analog waves into
    digital data.
   The DAC will reverse the process of the ADC
    to reproduce the original analog signal.
   Rather then having separate ADCs and DACs,
    soundcards will often integrate these into a
    single chip called a CODEC
   1/8 Inch (Most Common)
       The standard headphone jack
       Can only handle two channels
   Optical
       Very small connection, digital connection
   Coaxial SDPIF (Sony/Philips Digital Interface)
       Using the RCA connect, digital connection
   Two popular connects used in computers today
       AC’97 – Created by Intel in 1997
       HD Audio – Also created by Intel in 2004

   These are generally used for internal CD drives

   Most modern motherboards have connects for
    both.

   HD Audio is able to support 32-bit sampling
    resolution
       Most hardware manufactures don’t support this yet.

								
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