A simple question on converting sound wave into electrical wave

Discussion in 'Wireless & RF Design' started by AlwaysNumber1, Feb 12, 2017.

  1. AlwaysNumber1

    Thread Starter Member

    Dec 4, 2016
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    When sound wave is converted into electrical wave, is the electrical wave a sinusoidal with constant frequency and amplitude ?
     
  2. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Only if you are a good whistler. Connect a mic to a scope and watch. The electric "wave" follows the frequency and amplitude of the sound wave.
     
  3. AlwaysNumber1

    Thread Starter Member

    Dec 4, 2016
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    But why then everyone else draws this signal as constant while describing modulation ?
     
  4. BR-549

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    Sep 22, 2013
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    Because it's easier to see, and understand. Also unlike our voice, our test generators use nice sine waves. Our voice waves change too fast for our eyes to see. But if we use a symmetrical sound pattern.......it's easier to use and measure.
    Does that make sense?
     
  5. AlwaysNumber1

    Thread Starter Member

    Dec 4, 2016
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    Yes, it does
    But if the picture that we see in the oscilloscope represents our real voice, how will the diode cut off bottom part of the signal without destroying it >
     
  6. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    A diode does not destroy a signal. It rectifies it. It cuts it in half and only allows one side to pass. It will select either the positive part or the negative part. The positive part is a mirror of the negative part.......and vice-a-versa. They are mirrors. They are equal.....just inverted. SO.......we only need one. This would be called half wave rectification.

    But if we use more than one diode........we can flip the half that was discarded........and add it to the one we saved.

    That's called full wave rectification.
     
  7. AlwaysNumber1

    Thread Starter Member

    Dec 4, 2016
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    Aaaaa
    So even though the signal is constantly changing, the upper part is still the morrow of the down part ?
     
  8. BR-549

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    Sep 22, 2013
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    Yes......but see how much easier it is to understand with sine waves? The voice wave is too fast and irregular to try and see it. But with a sine.....you can see it very well. Whistle steady into the mic and see.
     
  9. BR-549

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    Sep 22, 2013
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    When we listen to audio.......our brain does not listen to every little component of the sound. Our brain detects the average amplitude and average frequency. It listens and detects the envelope (average) of the sound. Our brain catalogs envelopes. These envelopes are patterns. This is why we can understand a word that comes from different people. The individual sound is different.......but the pattern is the same.........or close to it.
     
  10. AlwaysNumber1

    Thread Starter Member

    Dec 4, 2016
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    Thanks a lot then !
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    No, it will vary in frequency and amplitude.
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    Everyone does not do this. A carrier maintains it's frequency, but the envelope reproduces the audio modulating signal.
     
  13. Papabravo

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    Feb 24, 2006
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    The modulating signal does the same thing to the positive half cycle as the negative have cycle. They are mirror images of each other.
     
  14. PhilTilson

    Well-Known Member

    Nov 29, 2009
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    Both BR-549 and Papabravo have said "The positive and negative half cycles are mirror images of each other". Whilst I understand why they have said this, and whilst it makes it easier to explain the basic case to the OP, it's not actually true!

    This only applies to a constant repetitive waveform. In the case of, for example, human speech, whilst the positive and negative half cycles will be very similar, by the very nature of the input, they will not be identical or mirror images. I only mention this because, if I don't, someone else will, and probably won't be as polite! :)
     
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  15. crutschow

    Expert

    Mar 14, 2008
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    It is true for an AM modulated signal, which is what they are referring to.
     
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