Editing unwanted noises out from Audio

Discussion in 'Video Cameras' started by Rob Beattie, May 28, 2004.

  1. Rob Beattie

    Tony Morgan Guest

    The fact that you express such a view illustrates that you have no
    understanding of digital signal processing (indeed nor of analogue
    signal processing).
    Indeed. But you were not so anxious to demonstrate that a little
    knowledge is dangerous, you would have noticed that I mentioned this in
    passing.
    Indeed. Perhaps I can quote me exact words (in this context)?

    "To do it by doing an FFT and isolating the cough spectrum in
    isolation".
    Clearly you're level of knowledge hasn't reached the stage of
    understanding that the cough is not a single sinusoidal waveform but a
    complex comprising a large number of individual components - each with
    it's own phase/amplitude vectors. And you obviously level of knowledge
    doesn't stretch to the fact that the cough complex (in all its
    components), if applied in antiphase to the original, will cancel the
    original - including all phasal variations.
    Exactly. But I guess that you have to accept the fact that (as I
    mentioned) that a signal processor to do it by FFT at £300K is outside.
    Did I say it is not so done?
    Indeed they do. The RAF use it in their TEW and ATA systems, The RN use
    it in their sonar target detection and analysis systems.
    Ummm... That's interesting. The Home Office had two such systems three
    years ago.
    You're clearly one of those who have decided to demonstrate that a
    little knowledge is dangerous - very little knowledge in your case.

    Try using Google (if you're prepared to open your mind up a little). Try
    this for starters:

    http://www.manukau.ac.nz/departments/e_e/research/staff/kot.pdf

    I should also mention that such noise cancelling has been used way back
    in analogue only days - though not in audio rather in analogue video. A
    classic example is that of the anti-clutter systems used in ASV13 in the
    Shackleton ASW systems. Used to selectively pick out submarine snorkels
    from the background wave clutter

    More recently, this same signal processing technology has been applied
    to oximetry in medical monitoring, have a look here:

    http://www.masimo.com/IMAGES/technology/lab1035.pdf

    I would urge you, if you know nothing, try to repress your inclination
    to advertise the fact.

    Scoffing those who know more than you might do something for your ego,
    but does little for your credibility.
     
    Tony Morgan, May 31, 2004
    #21
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  2. Rob Beattie

    Keith Laws Guest

    You will affect the phase if you convert the audio to analogue and do
    the filtering there, but WTF would you do that when you already have it
    digitally and filtering is just a case of doing maths on the signal?

    --
    Keith Laws

    What's my solution?

    .....NOISE POLLUTION
     
    Keith Laws, May 31, 2004
    #22
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  3. Rob Beattie

    Tony Morgan Guest

    I've had a quick look at Sonic Foundry (which is, BTW, built into Vegas
    4), and there appears to be a tool called 'dynamic gate' which would
    seem to offer the facility that is required, though I've never had cause
    to need or use it.

    I suspect that Martyn is an old-fashioned audio engineer who hasn't got
    around to understanding the power and potential of what can be done with
    DSPs.
     
    Tony Morgan, May 31, 2004
    #23
  4. Rob Beattie

    Keith Laws Guest

    I think *you* should do the maths,[/QUOTE]

    Have done thanks, I worked on active noise control in confined spaces (a
    bit like what Lotus offer(ed?) on some of their cars, but for a
    different application. Built a demonstrator, programmed the DSPs
    (including having to write functions to do the required complex
    arithmetic (as in sqrt(-1) not "difficult")) and had a successful
    result.
    --
    Keith Laws

    What's my solution?

    .....NOISE POLLUTION
     
    Keith Laws, May 31, 2004
    #24
  5. Rob Beattie

    Tony Morgan Guest

    Then you should know better than spout the dismissive rubbish that you
    have here. And going on about your brother doesn't add credibility,
    though while Googling, I had a browse through the synopsis to the book
    by Simon Godsill (your brother being cited as co-author) which seems to
    put your dismissive uninformed rant into perspective.
     
    Tony Morgan, May 31, 2004
    #25
  6. Rob Beattie

    Tony Morgan Guest

    Have done thanks, I worked on active noise control in confined spaces
    (a bit like what Lotus offer(ed?) on some of their cars, but for a
    different application. Built a demonstrator, programmed the DSPs
    (including having to write functions to do the required complex
    arithmetic (as in sqrt(-1) not "difficult")) and had a successful result.[/QUOTE]

    I suspect that Martyn's knowledge/experience ran out with Butterworth
    filters. Lots of capacitors, inductors and things.

    DSPs ? FFTs ? Oooh....errrr.... that's new-fangled stuff :)
     
    Tony Morgan, May 31, 2004
    #26
  7. At last, what I always considered one of the most unfathomable sigs,
    if not the silliest, begins to make sense. :)
     
    Malco1m Knight, May 31, 2004
    #27
  8. There is noise-reduction software that, shown a sample of the unwanted
    noise, will endeavour to remove it from an audio file, or a nominated
    portion of the file. The Waves Restoration plugins are a good
    example.

    These can be remarkably effective if the problem is a constant hum or
    "mush". As long as you have an otherwise silent segment - a very
    short length will do - the program will "learn" this sound and make an
    attempt at removing it.

    There are also programs that specialise in identifying and removing
    clicks and pops from an audio track.

    A cough falls in between these two. It's probably too long to be
    treated as a glitch, where the program would just cut that brief
    section then attempt a waveform restoration. The "learn and destroy"
    technique might be worth a try. If they aren't on top of dialogue
    splicing in a portion of ambient sound from another part of the track
    is a standard technique. It doesn't affect sync when done
    appropriately.

    Otherwise, I guess we're describing why there's a generally-used
    professional procedure called "re-recording".
     
    Laurence Payne, May 31, 2004
    #28
  9. Rob Beattie

    Tony Morgan Guest

    LOL. True. And perhaps an argument for NOT using the camcorder's inbuilt
    mic - which seem to be (almost) omni.

    Which reminds me. Those who've looked at the Sounds page on my website
    will remember the Argos wireless mic. Well now I've got the two-mic
    version (named - what else - Karioke). Virtually the same as the
    original one, with the addition of a second 'channel' through a
    mount-on-belt unit into which you can plug in a mic of your choice. To
    make it complete (since the receiver is powered by a 12V/mains power
    unit), I've found a small 12V spill-proof lead-acid battery at Maplin
    for £4 to make the whole system usable anywhere. This battery gives me
    just under four hours continuous operation which (for me) is enough.

    I know the sound gurus will sniff, but for my purposes it offers an
    inexpensive way of greatly extending my sound capabilities - especially
    as I already have various mics that I can use with the belt unit.
     
    Tony Morgan, May 31, 2004
    #29
  10. Rob Beattie

    Keith Laws Guest

    Pop Will Eat Itself Preaching To The Perverted lyrics:

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    For what you're about to receive
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    The boozers, the ugly, the crazy,
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    The perverts, the lazy...
    The trouble here is that trouble never happens
    There's bubbles to burst
    So making trouble's a first,
    Rhythm and rhyme, partners in crime;
    Going for the prime time-
    I'm gonna get mine.
    CHORUS
    This is the law-don't argue
    This is the law-stop grinnin'!
    Make some noise-shake what you've got...
    Go ahead-kick a hole in the speaker
    This is the law-for the ugly,
    This is the law,
    U-u-ugly oh yeah!
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    Very metal riffs polluting the air,
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    Say it loud and say it proud
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    What's my solution? Noise pollution!
    CHORUS
    This isn't love
    It's just cheap entertainment,
    The stains on the sheet and the crap on the pavement
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    Say what's got to be said with a sledgehammer,
    No s-s-stammer...
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    Each little excerpt, a feature of expertise
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    Perverts can you hear me?
    CHORUS



    --
    Keith Laws

    What's my solution?

    .....NOISE POLLUTION
     
    Keith Laws, May 31, 2004
    #30
  11. Rob Beattie

    Dave R Guest

    Oh the irony.

    And you guys were almost getting along last week!
     
    Dave R, Jun 1, 2004
    #31
  12. Rob Beattie

    Tony Morgan Guest

    Still are.

    Wouldn't the world be such a dull place if everyone had the same views?
     
    Tony Morgan, Jun 1, 2004
    #32
  13. Rob Beattie

    Dave R Guest

    Yes it would indeed. Although we could do without the bar fights, road
    rage, riots, wars etc. If only people learned tolerance of differences.
    :)
     
    Dave R, Jun 1, 2004
    #33
  14. Rob Beattie

    SjT Guest

    There's nothing i like more than finding a love letter from Tony
    Depends if it was overlooking the playboy pool. ;D
     
    SjT, Jun 2, 2004
    #34
  15. Rob Beattie

    Tony Morgan Guest

    The subtleties of that escape me I'm afraid.
     
    Tony Morgan, Jun 2, 2004
    #35
  16. Rob Beattie

    Mark A Guest

    The view would be a several scantily clad bunny girls?

    Regards

    Mark
     
    Mark A, Jun 2, 2004
    #36
  17. Rob Beattie

    Usenet Guest

    1. I'm presuming you have some kind of digital editor.

    OK- despite what anybody else says here about anti-phase/FFT/etc, the
    likelihood is that you will not be able to completely get rid of the
    cough unless it's occurring in places where you can simply mute the
    audio during the cough. If the latter is the main case, then the bits of
    the video where you've muted will sound a bit strange so copy parts of
    the audio where there's nothing important (dialogue, music, cars going
    past) of the same length of the cough and paste/mix them into where the
    coughs were. By tweaking the fade levels you can normally get the
    soundtrack to sound quite good.

    If your coughs happen while something significant is happening on the
    original sound-track then you're going to have to be more inventive. If
    the cough is very quick you can use an effect plug-in called a
    noise-gate which can quickly mute or lower the volume (called 'ducking')
    during the cough. This can make it much less obtrusive.

    If your editing system is a bit smarter then you can use something
    called Multi-Band Dynamics, which varies the volume but only at certain
    frequencies. This means you can tune the filter to the broad range of
    frequencies covered by the cough and, again, duck the volume, while
    hopefully maintaining whatever else was being recorded, but it'll never
    completely get rid of it, just make it more acceptable.

    You could try and use DSP software (usually termed de-noising), but the
    plugins are pretty tricky to use on a transient signal like coughs and
    usually work better on steady noises, like air-conditioning.

    As suggested, you can try copying just the coughs to another audio-track
    and the inverting/phase reversing them, then mixing them back against
    the original track so the coughs cancel out, or are at least softened
    (try mixing it with the copied coughs at a lower volume so they just
    take the power out of the original coughs but don't completely cancel,
    so you're still left with some ambient noise). I've never had a lot of
    luck using this method and it seems to take an age to edit them. Plus
    the slightest change in timing between the coughs completely buggers it
    all up (or using an effects).

    Finally, listen to it afresh and try to imagine if the coughs are really
    annoying to anyone else or just yourself. Being the cougher, you might
    think they're really obvious, but in many cases a viewer won't notice
    anything if only watching it once or twice.
     
    Usenet, Jun 26, 2004
    #37
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