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question about pcm

Discussion in 'Audio' started by eoin5, Mar 9, 2003.

  1. eoin5

    eoin5 Member

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    if you have a piece of digital audio made up of many instruments, how can a single sample represent the sounds? all it is is a 16bit number. also how does increasing the sampling rate let you hear more high range instruments like a high hat? please help me i have to write a paper on this stuff
     
  2. tigre

    tigre Moderator Staff Member

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    > how can a single sample represent the sounds
    It can't. Sound = Changing (usually) air preasure, perceived by ear. Loudspeakers cause changing air preasure by membrane movement caused by electric current changes caused by amplifier ... .
    If you make a curve of this electric current change, cut this curve in equal "time-slices" and measure the current for one of those slices you get a sample value.
    Every sound consists of and can be transformed mathematically into a combination of sinus waves. A sinus wave is defined by frequency, amplitude and phase (delay). To get those 3 variables for 1 sinus function, you need 3 sample values. So 1 sample value contains no audible information.
    One instrument (or a single tone played by 1 instrument) contains several sinus waves that are added, a lot of these are added again and result in the signal (it's the same e.g. in analog vinyl recordings, just not cut into slices with discrete sample values).


    > how does increasing the sampling rate let you hear more high range instruments like a high hat?
    Nyquist Limit: The maximum frequency that can be represented by digital signals is 1/2 of the sampling rate. The higher the sampling rate the higher the frequencies that can be included in the signal.

    You have to write a paper? Some keywords for google: "Nyquist Limit", "A/D conversion" (or "analog digital conversion"), "fourier transformation", "cosinus transformation", "sampling rate", "psychoaccoustics" ... (I guess you've already searched for things like "sound", "digital audio" before you asked this here.)
     
    Last edited: Mar 10, 2003
  3. cd-rw.org

    cd-rw.org Active member

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