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Is half of a soundwave, really a sound?

  1. Jul 4, 2013 #1
    Hi Guys!

    I am intrested in physics as amateur and this is my first post so be nice please :) What I wonder is about soundwaves but I don't know if this is the right section to write... If not, you may move the thread to appropriate section.

    My question has two steps.
    1. I have a soundwave in 686Hz. In music, it is somewhere between G4 and G#4. But I am producing only 1 wave. The expansion of half wave in the air will be half of a meter (as the speed of sound 343m/s.) and it will create a pulse on the eardrum for a duration of 1/686 seconds (1.45 ms.)

    Is human ear capable to hear that short duration of impact? If it's pratically "yes", would it still be a perceptible G4 or G#4 sound?

    2. If the above answer is "no" then, let's assume it is theorically "yes".
    This time I have a 343Hz. soundwave. It is somewhere between G3 and G#3 in music. But somehow I succeed to put out only the half of 1 wave. The length of the half wave will be half of a meter and the perception in the ear will be like the example above again. As I said before, let's assume that we can hear such short duration of sound.

    Then, would half soundwave still be a semantic sound can be perceived by human ear or any testing device?

    Thanks a lot!
     
    Last edited: Jul 4, 2013
  2. jcsd
  3. Jul 4, 2013 #2

    CWatters

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    Not very helpful but..

    http://www.e2s.com/knowledgebase/decibel-ratings.asp

    One problem is that hearing involves more than just the ears. The brain is involved in the process. For example ears can physically respond to some low frequency sounds yet the brain doesn't hear them.
     
  4. Jul 4, 2013 #3

    CWatters

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    Perhaps worth a read...

    http://music.columbia.edu/cmc/musicandcomputers/chapter3/03_03.php

    In short only a continuous sine wave is composed of a single frequency. A wave of any other shape is made up of a range of frequencies. Your half sine wave has a discontinuity (sharp transition) at the start and end that requires a large range of frequencies to reproduce.
     
  5. Jul 4, 2013 #4
    To get a sense of the frequency you require a few cycles. The shorter the duration of a sound the less it will sound like a note. In the limit of very short pulses it will just be a click.

    I don't think half a cycle will be distinguishable as any sort of note.
     
  6. Jul 4, 2013 #5
    First of all thanks a lot for your literature search, CWatters.

    What I mean by hearing is the full perception process, yes, including to be annotated by the brain, too...

    So I think my first answer is:
    According to your quoted passage, I understand that is obviously I will hear a less sound with the durations below 70 ms. and it will be only an impulse which won't be a meaningful sound anymore like G#4. Maybe even, I will hear nothing due to loudness of the sound.

    And my second answer is:
    There is nothing such a 'half soundwave'. Only a complete sine wave can produce a single frequency which can be defined with a single function. My 'half soundwave' needs fourier series to be defined which means, in fact, it is a made-up wave by different range of frequencies. Actually, it is not half of a single wave.

    They were really clear sir! Thanks a lot :)
     
  7. Jul 4, 2013 #6
    Yeah, I started to think the same. They will be just pulses on the eardrum and will only click.
     
  8. Jul 4, 2013 #7
    I tried some experimenting.

    Firstly, it is possible to distinguish tones as short as 5ms. Secondly, although hearing is not accurate at low frequencies it is quite possible to distinguish half-wavelength "tones" at 100Hz and 83Hz.

    I will shortly post MP3 files demonstrating this.
     
  9. Jul 5, 2013 #8
    While it is definitely possible to produce and possibly store a half-wavelength 'tone' ( a ramp wave is easily done ), the production of this electronic half-wave input into a half wave sound at the ear is impossible.
     
  10. Jul 5, 2013 #9
    Is "half-wave" really a "half of a sine wave" or a wave which is made up of a range of frequencies by using fourier series? After MrAnchovy's answer, I thought that I can do the same experiment with Adobe Audition. I succeed to reproduce a perfect half-wave. What I wonder is the wave calculation on the backround is really like as it meets the eye on the screen?...
     
  11. Jul 5, 2013 #10
    Fourier, though I am not sure what the expansion is, you could maybe try that yourself.

    If your oscilloscope is sensitive enough, you should see ringing at the start and end of the half sine-wave. I am not predicting how pronounced that would be because it would depend upon the electronic circuit producing the half sine wave.

    To produce the sound, you need to send it through a speaker, send it through the air to your ear drum. Since speaker, air, ear drum are all compossed of masses, and a mass takes time to react to a force ( the velocity does not change from one value to another instantaniously - the acceleration of the speaker cone and ear drum cannot be infinite ).

    The speaker cone after exitation from the half-wave will need a 'relaxation' to return to its resting position. There could be ringing sounds produced at the speaker also around the resting position depending upon the damping of the speaker.

    If you know the math it might be a good exercise to investigate how close you can achieve an actual half-wave from an ideal half-wave. And whether or not the ringing I mentioned are of frequencies that the ear is even sensitive to.
     
  12. Jul 5, 2013 #11
    Further investigation (see the image below, the top line is the generated tone the bottom one is as recorded by a microphone placed near a loudspeaker) shows two things:
    1. A half wave segment produces an audible tone one octave above the pitch of the full wave; this could be expected from visual analysis of a half wave segment and I suspect would be confirmed by Fourier analysis.
    2. The signal recorded by the microphone shows some "ringing" at the doubled frequency but:
      • this is at much lower amplitude than the input signal; and
      • this may well be an artifact introduced by the microphone - the recorded signal sounds less "clicky" than the original signal, indicating that higher frequencies have been attenuated which may zero the "ringing tail"
      It therefore seems fair to say that pitch can be audibly differentiated for tone pulses of duration of the order of 10ms, or 1 wavelength.

    If you are interested in hearing this for yourself, here are links to two files: http://www.mranchovy.com/wp/wp-content/uploads/2013/07/tracka.mp3 [Broken] and
    http://www.mranchovy.com/wp/wp-content/uploads/2013/07/trackb.mp3 [Broken]. One is a repeated half wave at 100Hz of 5ms duration, the other alternates 100Hz and 83Hz. See if you (and your PC speakers) can tell the difference.

    [Broken]
     
    Last edited by a moderator: May 6, 2017
  13. Jul 5, 2013 #12
    Great thanks MrAnchovy. Now it's all clear!
     
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