Removing background noise from audio track

Discussion in 'Professional Video Production' started by Code Developer, Sep 8, 2003.

  1. I was recently given a Digital8 tape to transfer to DVD. The content has now
    been captured to an AVI file using Adobe Premier, ready to burn to disc.

    The video is of a presentation being given by a number of people, speaking
    at the front of a large room. There is no PA system being used - the speech
    is being picked up by the camera (half way down the room) using the built-in
    mic only. Consequently, the speech isn't as loud as it should be. On
    increasing the volume, the background noise also increases noticeably (I
    think the background noise is from refrigeration equipment at the back of
    the room).

    Does anyone know of a way to eliminate the constant background noise,
    allowing me to increase the volume of the speech only?

    Thanks for any help.

    Regards,
    Shaun.
     
    Code Developer, Sep 8, 2003
    #1
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  2. Really effective noise reduction is expensive, time consuming,
    requires sophisticated hardware/software, and isn't as effective
    as you think. In other words, you probably shouldn't worry about
    it unless the customer has deep pockets and a very good reason
    to want to improve the signal-to-noise ratio.

    The most sophisticated post-production noise reduction process
    is nowhere near as effective as simply placing a microphone in
    the proper place.

    Others may suggest all sorts of remedies, but when all is said and
    done, you will find that you should either plan on spending big money
    on this, or else just forget it. At least that is my conclusion after
    several decades of produciton and post-produciton in sub-optimal
    conditions.
     
    Richard Crowley, Sep 8, 2003
    #2
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  3. Alas, CE2K is no longer available (for any price).
    See the link cited above. Thanks a lot, Adobe! :-(

    While CE2K's noise-reduction capabilities are quite effective,
    I have my doubts about its ability to handle such a
    diffuse source as the OP cited.
     
    Richard Crowley, Sep 8, 2003
    #3
  4. Damn! I waited too long to pick up the 4-track module at a reasonable price!
    And now Cool Edit (ahem, "Adobe Audition..." ) is three times the price
    it was...
    It works well for this for me, though it may be necessary to
    choose intelligibility over low artifacting...
     
    David Ruether, Sep 8, 2003
    #4

  5. Thanks for the info guys.

    It's a pity that Cooledit has been discontinued. I read a number of other
    posts also suggesting this software , and I intended to try the trial
    version tonight :-(

    Just to clarify, I don't think the background noise is too diffuse to be
    eliminated by the right filter(s). After all, it is a fairly consistent
    low-level noise produced by one refrigerator in the room. However, I'm no
    expert on audio filtering, so I won't know until I try it.

    Regards,
    Shaun.
     
    Code Developer, Sep 8, 2003
    #5
  6. Code Developer

    Jay Rose CAS Guest

    Read the feature article on noise reduction at DV.com. It includes
    techniques, pointers to various products (ranging from free to $$$),
    things to do before using NR software, and how the stuff actually works.
    Most people don't really understand the process.

    If this is low-level noise AND there isn't too much echo on the voices
    (you said the mic was how far back?), it'll probably clean up pretty well.
     
    Jay Rose CAS, Sep 8, 2003
    #6
  7. Code Developer

    Mike Rehmus Guest

    Try reading some of the Jay Rose columns in DV Magazine or his book on Post
    Production. Otherwise, right now, you may need to buy Sound Forge with the
    noise reduction module (it will reduce the hum) or the Adobe version of Cool
    Edit Pro. Called Edition?
     
    Mike Rehmus, Sep 8, 2003
    #7
  8. Code Developer

    MSu1049321 Guest

    parametric equalizer, and/ or downward expander. I love Ray Gun on the mac. It
    was 50 bucks. If you browse some of the computer music type magazines at
    barnes & noble, many of them come with freeware or shareware recording programs
    and plug-ins. Look for a compressor/expander plug-in, and a parametric EQ
    program.

    One other thing you might try if you have an audio mixing board would be to
    feed the same signal in on two channels and use phase cancellation to kill the
    identical continuous noise on both tracks while a somewhat attenuated signal of
    the speech passes through. Not as good, but you work with you you have
    sometimes...
     
    MSu1049321, Sep 8, 2003
    #8
  9. Code Developer

    Jay Rose CAS Guest

    How on earth would that work? If you're feeding an identical signal to two
    identical board channels, using phase inversion would cancel both the
    noise and the signal equally. Do the math.

    Now if you _delayed_ one channel, you could remove harmonically related
    noise such as dimmer buzz (using a comb filter effect). But that's not
    what the op was dealing with.
     
    Jay Rose CAS, Sep 9, 2003
    #9
  10. Code Developer

    MSu1049321 Guest

    I guess I worded that poorly... what I was trying to get at was, maybe you run
    one channel of just the room tone with the noise against the vocal track with
    the same noise, and you play with the phasing and levels until the out of phase
    noises cancel.... Aghhh, maybe it wouldn't work after all... you'd need very
    precise control of the timing, among other things....
     
    MSu1049321, Sep 9, 2003
    #10
  11. Code Developer

    thrillcat Guest

    Another nice NR plug in is Noise Reduction 2.0 from Sonic Foundry
    (www.sonicfoundry.com). It'll run you a couple hundred bucks, plus you have
    to run it within Sound Forge (I haven't tried it in competitor's software,
    but it may work), or you could pick up Vegas 4.0 and have a second video
    editing application as well. It's a personal preference, but the more I
    used Vegas, the more I hated Premiere, to the point that I no longer use
    Premiere at all (although I've heard many good things about the newest
    version).
     
    thrillcat, Sep 9, 2003
    #11
  12. Code Developer

    Max Volume Guest

    Well, CoolEdit (at least 2.0) can try to extract just the noise from an
    audio file, then use that data for it's noise-reduction filter. You
    can hear just the "noise" that CoolEdit has extracted just in case some
    valuable frequencies are in there, and of course you can typically
    "Undo" your actions if you have "Undo" enabled, which I recommend.
     
    Max Volume, Sep 9, 2003
    #12
  13. message
    A quick update on the problem.

    Last night I spent a bit of time working on the audio track and
    unfortunately it appears that it is not going to be an easy task (if at all
    possible) to remove the noise.

    I did a spectrum analysis on a small section of the sound file containing
    both normal speech and a 'silent' section. This showed up the following
    points :

    There are a number of distinct frequency bands generated by the equipment
    (100Hz, 680Hz being the loudest, plus a couple of others). These are easily
    removed using some parametric or notch filtering in Premiere, without
    altering the quality of the speech too much.

    The spectrum analysis also showed a lot of white noise across the frequency
    range of 40Hz to around 6kHz). Unfortunately the signal level is not much
    higher than this noise level in places as the camera mic is so far from the
    people giving the speech. I have a feeling that it may not be possible to
    separate the two in places.

    I notice the replies above suggest a few places to look for advice on
    filtering, so I'm going to check them out later. Also, I'm really only
    looking for shareware or freeware utils, as it's not often I need to go this
    in depth when copying over video to dvd. I couldn't really justify spending
    £200 on software I'll probably only use once or twice.

    Thanks to all who replied.

    Regards,
    Shaun.
     
    Code Developer, Sep 9, 2003
    #13
  14. Code Developer

    Ty Ford Guest

    Hey Richard,

    I'm surprised max hasn't called you out for being a imperious technoweenie
    with various mis-matched parts of your body inserted where they don't
    belong. He must be back on his meds. We like him better that way.

    Roland had a box that removed HVAC noise incredibly well. We tried two types
    of HVAC noise. I remember one was more 60 120Hz centered. We had the best
    results with that. The other HVAC noise was more broad spectrum. It got
    cleaned up, but not as well.

    I have an old CRL hardware box that does a pretty nice job. It's similar to
    the symetrix unit. The GML isn't made anymore. Cedar has a box based on the
    GML; pricey, but effective.

    I use Spark XL software and the CRL box for that sort of thing.

    Regards,

    Ty Ford


    For Ty Ford V/O demos, audio services and equipment reviews,
    click on http://www.jagunet.com/~tford
     
    Ty Ford, Sep 9, 2003
    #14
  15. Mr. Ford. Do you seriously think that someone who can afford
    Cedar would be working with such source material and posting
    such a question in Usenet? Go back and read the OP again,
    carefully. Note that his "sound track" was from the on-camera
    mic in the middle of the room. Even the desired signal is diffuse,
    and it wouldn't surprise me if the SNR is <10dB

    We're not helping these transient amateurs (no offense intended!)
    by pontificating about all the latest/coolest whiz-bang high-tech
    solutions when they are unlikely to even understand them, much
    less afford them.

    I'd bet that only a tiny fraction of the people who come here with
    noisy sound tracks ever get anything like the remedy they are
    seeking. They watch too much impossible magic on TV and
    think it is reality. Best to learn from the mistake and use better
    micing techniques next time.
     
    Richard Crowley, Sep 9, 2003
    #15
  16. Code Developer

    Steve King Guest


    My understanding was that a client who shot or had shot the video brought it
    to the original poster who was trying to improve it if possible. Which is
    what I would do if one of my clients brought in such a tape, and they damn
    well can afford what's necessary if the need is great enough. Of course I
    could just tell my client that he's an idiot and go away. Like, that is
    likely. Why bring out your "they're all idiots" POV, Richard? Makes you
    look pretty arrogant. You have alot of knowlege but you sure can be a pest
    sometimes. Have another cup of coffee.

    Steve King
     
    Steve King, Sep 9, 2003
    #16
  17. Code Developer

    Dennis Vogel Guest

    Does Vegas have NR features in it? Does the Sound Forge
    NR package work in Vegas?

    Dennis Vogel
     
    Dennis Vogel, Sep 9, 2003
    #17
  18. Use Noise Reduction with Sound Forge® 6.0 or any other DirectX-compatible host
    application to clean up your audio files and achieve professional results.

    http://www.sonicfoundry.com/Products/showproduct.asp?PID=14
     
    Charles Tomaras, Sep 9, 2003
    #18
  19. Code Developer

    David McCall Guest

    --

    The short answers are No, Yes
     
    David McCall, Sep 9, 2003
    #19
  20. Code Developer

    Max Volume Guest

    HA! Thanks, Richard. Couldn't have said it better myself. ;)
    True. However, CoolEdit is a hell of a lot more accessible to most
    than a rack-mount Symetrix or other brand hardware, hence my
    suggestion.
     
    Max Volume, Sep 9, 2003
    #20
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