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Audio Jack Mystery

  1. Jun 1, 2015 #1
    Hello everyone :)

    I came across a strange situation today when I was listening to my music with my headphones on. When I pressed play to a song, the instrumental intro started off fairly normally (although the audio sounded a little "thinner" than usual, as if compressed), and then, when the vocals were meant to kick in, they didn't! I was very surprised since the instruments kept on playing normally!
    At first I thought that it was a strange glitch within Spotify, and I thought that maybe they had an odd way of encoding different "layers" of audio. So then I tried iTunes, YouTube etc. and it was the same again...some elements of the sound were there (people talking in the background), and some were completely silent (main character talking). I always thought that audio files, especially ones that would be used for streaming, would only have one waveform (2 for L/R stereo) encoded on them.
    When I unplugged my headphones, everything was ok through the speakers, so I suspected a faulty sound driver. After restarting and updating (MacBook Pro), I still had the same issue. I plugged in my headphones into my phone, and to my surprise, the exact same problem occurred. My headphones are not noise cancelling, are not wireless, and receive an analog signal, yet it seems like they selectively, and very accurately, ignore parts of the raw audio signal.
    I checked my connection and noticed that the cable that connects to the side of the headphones was slightly unplugged (that should have been the first thing to check! XD), and when I pushed it in properly, everything was fixed.
    I simply cannot understand how a bad physical connection like that can be so precise in cancelling very specific parts of the audio. I doesn't make sense to me. Perhaps the cable to the headphones is acting like an antenna and transmitting the audio signal through that very small gap (the bad connection), and the frequency response my be causing the effect. However, it still wouldn't explain why parts of the audio with similar frequency ranges are still being passed through fine while others are not.
    Sorry for the massive post, but I would greatly appreciate any suggestions as to the reason :D

    Best wishes,
    Nat
     
  2. jcsd
  3. Jun 1, 2015 #2
    It sounds as if you had the 'phones connected between the two channels, between L and R. If you do this, the phones have the difference signal. The difference signal tends to include any incoherent sounds picked up my the microphone, such as room echo. Of course, when the stereo has been artificially doctored, anything is possible. With an ordinary stereo set up, if you connect a rear speaker across L and R, it provides a surround sound effect, because it re-inserts the background and ambience of the concert hall, including audience noise and reverberation.
     
  4. Jun 1, 2015 #3
    Ooh! That sounds very convincing. That's probably it then. I'll check to see what happens with a mono signal. Thank you very much for the quick reply! :D

    Best wishes,
    Nat
     
  5. Jun 1, 2015 #4

    meBigGuy

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    Gold Member

    If you listen between channels (this is, connect between left and right with no ground), the sounds that are normally centered will be gone.
    Generally the bass is centered, and would also go away.

    If you listen in mono, every thing will go to center, so then causing the issue will make everything go away.
     
  6. Jun 2, 2015 #5
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