Strange background noise from microphone input

Discussion in 'Computer Components' started by frogbrains, Dec 23, 2011.

  1. frogbrains

    frogbrains
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    Hello!

    I am having a slight (bit very irritating) problem with my onboard audio hardware (Realtek ALC833). The 3.5mm microphone in jack causes some very strange sounding background noise. A 10 second recording of said noise can be heard here.

    I know some of the noise is picked up from my computer's rather loud fans and such, but the noise I am referring to is the odd screeching and and regular beeps. It is not caused by the microphone itself, as I have tried it with a USB audio device.

    Any explanations and/or solutions?
     
  2. JefUK

    JefUK
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    The recording you posted was fine - no noise at all - only white noise with the playback volume turned full up? Did you make an error in the recording or is it a problem with playback?

    Onboard microphone audio often picks up electrical noise onto the cable from the header to the front ports, especially when the cable screening is poor. Noise can also be picked up from the motherboard due to the proximity of analogue signal tracks to the multitude of digital signal paths. It is one of the maor problems with onboard audio.
     
  3. frogbrains

    frogbrains
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    The recording definitely contains the background noise in question. It is rather quiet, as I did not amplify it at all. Regardless, I would have guessed that the problem was caused by poor cable screening or interference from the motherboard, as you said.

    So, is there any solution to this?
     
  4. JefUK

    JefUK
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    I have analysed your noise file with CoolEdit20000 and it shows that the microphone system noise level is less than -70dB over the whole spectrum - see attachement.

    This level of noise is very low for a microphone system and will be difficult to better, even with a sudio setup! On the basis of this analysis there is no improvement needed.

    Are you sure that the recording was made correctly, or that the problem is not with your playback system?
     

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  5. JefUK

    JefUK
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    Another analysis - same result - no problem!
     

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  6. JefUK

    JefUK
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    Another analysis to prove (to myself) that the noise is very low. This analysis shows that the highest noise level is a 50Hz peak, but even that is very low, below -60dB.
     

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  7. frogbrains

    frogbrains
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    Thank you for all your work on this.

    Although the noise level may be quite low, there is a regular "chirp" that appears to happen every second - it is this that causes issues with noise removal.

    The problem is definitely not caused by my playback system. As mentioned in OP, I have tried the same microphone using a USB sound card, and the noise is not apparent. In both cases, I am using the same USB soundcard for output to headphones.
     
  8. JefUK

    JefUK
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    To get better sound quality with your microphone, you could try replacing the cable from the motherboard to the front mic jack socket with a high quality screened audio cable. You would have make the cable yourself and fitting it could be tricky if you are not used to doing electronics work.

    A far better option would be to use an external microphone amplifier and connect it to the line input, or with the right amplifier to the digital input if your PC has one.

    Happy Christmas.
     
    Last edited: Dec 25, 2011

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