how to remove lights hum post filming?

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    • #48265


      I posted this question a while back and am still looking for answers. I need to film in my commercially leased workshop space. It has 17 massive metal halid lights who’s transformers produce a noticable humming noise when on. There are no windows in the space, so no natural light. I do use soft lights, but do not have enough to light a 2600 Sq. Ft work area. Replacing the existing light’s transformers is out of the question.

      I am hoping there is some way in editing the audio, I can at least reduce the humming noise? I use PowerDirector 8 and they have a very simple, on or off kind of audio noise reduction. Kind of just muddies the sound.

      I do use UHF collar mics for recording the audio. How do you run the audio through a filter, equalizer, whatever to remove noise? What brands can you suggest, how do you hook them up to your computer etc?


    • #198407

      You have a couple of options – 1) you can record a small amount of “silence” and then remove that from the whole using a noise reduction filter (Audacity has this and is free but so do many commercial sound editing packages like Sound Forge, Audition, etc…) or 2) add a filter to remove the specific frequency of the hum (Vegas has this as do many others).

    • #198408
      Grinner Hester

      because it’s constant, you’ll have no problem dialing in the freq and deleting it. A parametric eq is your buddy bud a regular 5 band will do it if you dink with it long enough.

    • #198409

      If you haven’t shot the tape yet, try to maximize the strength of the desired sounds by putting the mics as close as possible to the sound sources. Turning up the audio gain will not work and will make the hum worse. Also, be sure that any directional mics are oriented as to minimize the hum pickup. Finally, turn off any unused lights. You might as well check for other sounds such as fans etc as well.

      In post, the filter suggested by birdog is a good idea. This is not a filter in the classical sense. What you do is record some room sound which consists of only the noise and not any desired sound. The software then subtracts the digital pattern of the noise from the overall desired sound plus noise. I have done this in Adobe Soundbooth and it works pretty well. It is not perfect, however, so minimize the hum before recording it.

      You can try a notch filter, also included in most audio editing software. You set it for the hum frequency (60Hz in the US). It will probably be necessary to apply several notch filters at the harmonics of the hum (120 Hz, 180 Hz, 240 Hz etc) because the hum you are hearing is not sinusoidal.

      Finally, possibly the best solution is to add background music or other sounds to mask the hum.

      Good Luck!


    • #198410

      I have used, for some time, one or the other of two items of audio-cleaning software from ‘Magix’ of Germany, ‘Audio Cleaning Lab XX deluxe’ or its video equivalent. Both work superbly, especially if the video version is able to be invoked as mine is, directly from Magix’s MEP17 Video Editor timeline. However, both programmes will work in stand-alone mode, as well. (‘XX’ for current model number).

      Briefly, a portion of the sound-track is found which features only the unwanted sound and that is ‘sampled’. It is then ‘subtracted’ from the faulty track, as clean as a whistle in most cases. A typical case-in-point, being a wild-sound track I once recorded, with the highly characteristic ‘slap’ of small waves against the stonework around Dunedin’s Harbour, but ruined, for all practical purposes, by theincessant throbbing of a diesel engine running close-by. In that case, the sounds of the motor were removed with almost surgical precision. Numerous other examples come to mind, especially low-level ‘background’ traffic noise. I have tried other ‘solutions’, but found them difficult to use.

      Since the cleaning-up of sound-files is so effective and problem-free, I run every instrument track through the same process as a wave-file between ‘performance’ and the final downmix as well, (I’m talking symphonic ‘music’ here). That same software is just as effective for that. The AVS suite of video-making/editing/ processing software, from England now includes a very handy little audio-editor, with the same facility built-in, I have found. I have no recent experience of ‘Audacity’, having given up on it in on of its earlier versions due to out-of-synch problems between stereo-tracks, but it probably, these days, gives quite a good account of itself, as well.

      Ian Smith – Dunedin, New Zealand

    • #198411

      Thank you for this feed back. It raises, for me, some new questions. What kind/brand/product No. of parametric equalizer should I shop for. I have no idea? Do not even know where to start? How do you plug it into your system, computer? I need some more basic information. Smae questions for a “notch fliter”? What is it? where do you buy them?


    • #198412

      These filters should be part of your NLE or audio editing software – you can get Audacity (free) which will have them.

    • #198413

      Depending on the software that you use, you can reduce the ambient noise sound. I just figured out the other day how to do this in FCP. There are two different methods.

      Method 1:

      1. If you are in FCP, Right Click on your audio file> Send To > Soundtrack Pro Audio File Project.
      2. Once Soundtrack Pro opens, find a spot in the audio file where there is only ambient noise. Hissing for example. Highlight it.
      3. Process menu > Noise Reduction > Set noise print. (It will look like nothing happened but keep going.)
      4. Now, highlight any audio you wish to correct.
      5. Next: Process menu > Noise Reduction > Reduce Noise. (A HUD will pop up and allow you to adjust the level of correction.)
      6. After you have done this, got to FILE > SAVE.
      7. Once you return to FCP, the reference file will be in the Browser.

      Method 2:

      Follow all of the steps from Method 1 with the exception of Step 3. Remove this step. Then continue to the rest of the steps. If you use the default “REDUCE NOISE” settings, without setting a Noise Print, it sounds pretty good as well. This is the method I typically use.

      While this is the process within Final Cut Sutdios, I’m sure that Adobe and Sony have a similar process.

      Hope this helps.

    • #198414
      Grinner Hester

      If you really filmed it, you probably recorded audio on a nagra. You can run it through a parametric eq during transfer.

    • #198415

      Depending on the NLE software you’re using, you should have some basic audio tools/plug-ins already built-in. I know that Avid, FCP, Premiere and Vegas all have EQ, Noise Reductions, Normalizer, and Noise Gate plug-ins. Then there is audio software like Sound Forge, Sound Booth and now Audition just to name a few that have great sound editing tools that can clean unwanted frequencies without much difficulty. Last resort is to bring your interviewees in for voice-overs just in case you can’t salvage the field audio.

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