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Thread: Active Noise Reduction

  1. #1
    Maximum Bitrate Mañana's Avatar
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    Active Noise Reduction

    I just came up with a thougt.

    How about placing a microfone somewhere in the car, and then hooking it up to the computer. Then let the computer monitor the sounds in the car (enigne noise etc), and then you let the program send exatly the same signals to the speakers, but inverted. That would eliminate the noise and you'll get rid of (well, it'll probably not work 100%) all the noise! =D

    I know this already has been made, you can buy earphones that work this way, but still... Wouldent it be cool?

    Also, you could let it monitor any music that the pc sends out, so that it wouldn't try to get rid of it...

  2. #2
    I see dead kittens Quattro's Avatar
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    I don't know anything about this Active Noise Reduction thing, but it sounds really cool. I would how effect it would be.
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  3. #3
    Raw Wave RoyN's Avatar
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    I'm not sure if the speakers we use today are capable of sending that "inverse" sound wave...

    But yeah, it is basically the principle in noise-canceling headphones, and even the noise canceling equipment available on some private jets (I guess some airlines might have it already by now, it has been available for private jets for more than a couple of years)... basically it emits an "inverse" of the "noise" it captures. I think it wouldnt be easy though, as I believe it "predicts" the noise pattern based on the noise it has been hearing. That is how it can send the inverse-noise simultaneously with the "noise"...

    It probably wouldnt work very well accelerating or changing speeds/RPMs, but should be pretty cool at constant speeds.
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  4. #4
    Maximum Bitrate Mañana's Avatar
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    Quote Originally Posted by RoyN
    I guess some airlines might have it already by now
    They do =)
    Quote Originally Posted by RoyN
    I think it wouldnt be easy though, as I believe it "predicts" the noise pattern based on the noise it has been hearing. That is how it can send the inverse-noise simultaneously with the "noise"... It probably wouldnt work very well accelerating or changing speeds/RPMs, but should be pretty cool at constant speeds.
    Do you think that it'll need a buffer that big that it can't keep up with an accelerating engine?

  5. #5
    Constant Bitrate gizak's Avatar
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    I've thought about this too as a way to combat surrounding noise being intrusive to voice control programs. It must be hard to do or somebody would have it made already right?
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  6. #6
    Raw Wave RoyN's Avatar
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    What do you mean "buffer too big"... the buffer is like maybe the last .5 seconds or something... however, when accelerating there is a change of "constant background noise pattern", and until the noise stops changing the results will not be as good...

    it wont completely stops working as you accelerate or anything, but its efficiency is really with "constant background noise" that is the whole principle. it copies the constant noise, and sends out a inverted sound wave of that noise.

    Pretty cool, who has it already?
    Roy

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    Any ideas for putting a PC in this? :)

  7. #7
    C4M
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    That's a great idea! I'm going to build this into a hat, so that it cancels out repetitive droning music. Watch out Enya!

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  8. #8
    Raw Wave shotgunefx's Avatar
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    No expert by any means, but I thought one of the big challenges was the multiple paths sounds takes to get to you.

    A headset/mic is relatively easy as you dealing with pretty much fixed positions. Whereas in a car, the sound is coming to you from various paths. (direct, deflections)

    Unless the speaker was on or near your ear, it's not going to hear the same sounds that our ears do, so any inversion you do won't cancel (or completely anyway) out the noise. Something like that would probably be much easier to do with earbuds as they are at the same location and could invert in realtime. (Combining the headphone jack with what's coming in from the other side).

    I played with it a little while back trying to cancel the noise from my fans in my cpus. I only screwed with it an hour or two, but it did get me thinking about it.

  9. #9
    Variable Bitrate
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    I drive a Ferrari - why would I want to cancel out the engine noise?? !!

    Agree with the previous point though - I wouldn't expect it to work unless the device was placed in or very near to your ear.

  10. #10
    Maximum Bitrate grepzen's Avatar
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    The reason this is concept is exploited so handily in headphone form is that..
    » Noise comes from many different places places. Calculating the offset for the inverse signal is complex w/o also calculating distance to the ear. --let alone more ears (other passengers)
    •Micke

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