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Thread: Here’s A Digital Conundrum

  1. #11
    Join Date: Aug 2008

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    Okay, so if I have understood correctly during A/D the line between two samples is not smooth but actually modulated (squiggley) however, the modulation will be due to high frequencies that are far above those of interest and that can be acurately reconstructed during D/A, ie, Aliases 2 times above the Nyquist limit?
    ~Paul~

  2. #12
    Join Date: Mar 2011

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    Quote Originally Posted by Primalsea View Post
    Okay, so if I have understood correctly during A/D the line between two samples is not smooth but actually modulated (squiggley) however, the modulation will be due to high frequencies that are far above those of interest and that can be acurately reconstructed during D/A, ie, Aliases 2 times above the Nyquist limit?
    Nearly. During A/D you filter signals above 22 kHz as there is very little if any data above 22kHz. Now when you digitise the signal there is only signals up to 22kHz. If you sample the signal at 44 kHz then according to Nyquist sampling everything below 22kHz is digitised correctly. When you then go through the D/A in your DAC the system knows there are not any signals above 22kHz and the original signal is reconstructed with all the frequencies up to 22kH correctly reconstructed.

  3. #13
    Join Date: Feb 2008

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    Quote Originally Posted by George47 View Post
    Nearly. During A/D you filter signals above 22 kHz as there is very little if any data above 22kHz.
    There are harmonics of the audio data within 20Hz to 20KHz that extend above 20KHz.

  4. #14
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    Harmonics are created by and presumably interact with lower frequencies. If they are missing, could that affect the form of the fundamentals?

  5. #15
    Join Date: Mar 2009

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    Last edited by Patrick Dixon; 31-05-2018 at 10:22.

  6. #16
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    I do wonder about transients also. If they begin or end at a point between samples what happens then?
    ~Paul~

  7. #17
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    Last edited by Patrick Dixon; 31-05-2018 at 10:22.

  8. #18
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    They get ignored. But they would really have to be very narrow to get to that stage. I can hear tape noise from the original recording of Crazy by Patsy Cline, and also on the original recordings of many songs from Marvin Gaye. That kind of noise is like a transient, but it is still captured during the A to D process.

  9. #19
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    Last edited by Patrick Dixon; 31-05-2018 at 10:22.

  10. #20
    Join Date: Apr 2012

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    That's not exactly an answer helpful to non mathematicians who may appreciate a layman's explanation of the basics.

    And large bold is not really necessary (or polite?)!

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