Treating a studio that has central air

Discussion in 'Acoustics (Live Room, ISO Booths)' started by ianlucerofilms, Aug 1, 2018.

  1. ianlucerofilms

    ianlucerofilms Active Member

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    Aug 1, 2018
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    Portland, OR
    Hello I'm new here so please bare with me if I get certain terms wrong or am not describing the problem clearly. I'll try my best.

    I am a video/editing guy by trade but am a stickler for good sound and as many of you know sound can be the least important thing or last thing on anyone's mind on a set. Quick low-down on my situation... I currently work in the education system, at a university in fact, where a small video team of about 5 editor/shooters create online educational videos. At this point we have the lighting dialed in to the T but the audio is quite sub-par. I am the go to person for fixing the audio. Here's what's going on in the studio. It is a small green screen studio, except for the screen's material and maybe some sprayed-on acoustic treatment on the ceiling(if any) there is no other treatment for sound. For the most part we rarely hear traffic noise, or sounds from the rooms nearby. The room is located in the basement, so aside for the occasional music from the small gym a few doors down, it is relatively free from exterior noise. The problem with the room is the duct used for central heating/cooling and as you may know, we have no control over when it is on or off. I have done what I can to minimize the noise by removing the register to help with reducing turbulence and have also tried redirecting the air flow so there is less chance of it hitting the lavaliere mic on the talent. The latter is rarely an issue. Anyway, you can probably guess where this is going. After a shoot, sound files get sent to me and I do my best to clean things up using a variety of techniques(Adobe Audition's denoise or iZotope RX, applying Acon Deverberate, parametric EQ to boost lost frequencies, etc.)

    I am getting increasingly annoyed that I have to deal with such crummy sound while the picture looks so pristine. I would like to try and remedy the situation by fixing the problems before it even gets recorded. One editor suggested we aim two shotguns at the talent, balance it out in post with probably more clean up and call it good. I don't see how that would work considering the size of the room and how all encompassing the noise is. He also suggested it needs more egg crates. :facepalm: For the most part the noise is consistent which is great for the noise reduction tools but there are a myriad of speakers that come through, male, female, bass, tenors, altos, soft, loud, you name it. So denoise tools don't always work. Too many certain frequencies get removed.

    My questions are... is there ANY way to minimize the noise coming out of the one vent in that small space? The vent is about 4-5 feet above the talents head. Can there be something maybe placed inside the duct, prior to the air coming out, to help minimize turbulence? This might have to be done on the sly as to not disturb the cooling/heating system of the building. OR Is there something that can maybe catch the frequencies coming from the duct? Would bass traps minimize these annoying frequencies? Something maybe placed in front of the duct but still alloy it to adequately cool/heat? Is my co-workers idea of using two shotguns a good idea? Currently we use a lav and that goes straight to the camera. Would a better sound recorder set at a higher capture rate/resolution help with sampling the noise and thus giving me better denoise results? Although I'd rather not do so much post-process.

    I hope this illustrates my dilemma and hopefully someone out there in the community could shed some light on the subject. I'm all for setting up the source correctly, it's just a matter of how and then figuring out a budget to propose. Thank you in advance.
     
  2. kmetal

    kmetal Kyle P. Gushue Well-Known Member

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    if you could get some ducting of similar size, you could re-direct the air flow so it blows across the ceiling as opposed to down from it. im not an hvac expert, but there might be some sort of plug consisting of layers of cotton like a an air filter, that would slow the air velocity down. you could possibly add damper to the register to completely stop air flow, while recording, they make manual and electronic dampers.

    any sort of acoustic treatment wont do anything to help the air flow, but would increase the quality of sound captured, ie less room sound, more clear direct sound. so to me the room needs both HVAC, and acoustic work.

    what im curious about is if the air flow from the suplly register isnt getting into the lav mics, what exactly is your issue? in other words, is it mechanical noises, rumbles ect, or the actual air flow like wind noise getting into the mics. also are you using any other mics beside the lavs mics? are you recroding instruments or using room mics ect?
     
  3. ianlucerofilms

    ianlucerofilms Active Member

    Joined:
    Aug 1, 2018
    Location:
    Portland, OR
    My apologies, I should have been more clear about the direction and position of the air vent. The duct itself is right above the talent, running across the room, and the vent is facing not down but toward the camera/entrance of the room. So the air itself isn't hitting any of the sound gear nor the talent.

    I'm a little wary about putting more dampeners in the way of the airflow because I've had prior experience in my own house where the ducts and vents are much too small for the velocity of air coming through so attaching registers and filters or any sort of material at the point that the air exits created so much noise that we were better off just let the air flow with no obstruction. But that might be a completely different problem. I am not sure if the building maintenance folks would like us messing with the HVAC. As I had originally mentioned, removing the register to restrict the air less made it less noisy. To be more precise, it made it so less noisy frequencies were generated. That meant when I took a noise print less if the noise frequencies were captured so thus less frequencies were removed from the voice. I'm not 100% sure that's how denoise works but to my ears the vocals were then slightly clearer/cleaner.

    I totally agree. Even after removing the noise there is echo and I believe if we simply treated the room correctly(noise or no noise) to deaden the that room sound and also lessen the boominess, that would improve the capture as well as make it less complicated in the denoise process. Right now what I am finding is that because of the inherent sound of the room, it is magnifying the all the sound in that space. I am still relatively new sound capture and process but it is my understanding that in an untreated space, not only will you get delayed sound but also a build up of the sound being reflected over and over in the space. The biggest culprit of that energy source being the HVAC and the prolonging of that energy being the untreated room.

    Mainly I believe the noise is being generated by the turbulence in the duct itself as well as the air flow hitting the vent as it exits into the room. Removing the airflow register minimized the number of surfaces the air would hit, lessening the amount of noise frequencies overall. I think at this point I need to measure how loud the noise is compared to an average speaking voice and then figure out a strategy to treat the room. Although, I would still like to know if I am missing anything. For instance, is there a way to cancel out the noise? I have no clue if that is possible. Just a thought.

    --
    Oh also, thank you for your response Kyle.
     
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  4. pcrecord

    pcrecord Quality recording seeker ! Distinguished Member

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    If you are using an on camera mic, it's normal to get noise, even in a mute room. The mic and preamps most have are not good, I just wonder why the keep putting mics in cameras.. oh yes, if you need to record noises.. eh eh ..
    Shotguns are good tools but needs to be close and well aimed at the talent's mouth. If they need to move, it's harder to cope with unless you have an assistant that follows them with the mic.
    The best bet is to use lavalier mics. hidden under or on clothes, they are small enough so people don't notice them and even if they do, pro news ankers have them so everybody is used to see them.. it's not like a movie set, right ?
    I use the Tascam DR-10L with some succès, I like it because it has it's own recorder, so no wireless setup to maintain.

    As for dock isolation, they need to be analysed, do you hear the wind that exits the dock or the internal noise air produce while hitting the interior of the dock (at curves or L turns) ?
    In any case, I guess those noise wouldn't be disruptive if proper mics and placement were used..
     
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  5. paulears

    paulears Well-Known Member

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    why not use a mic to determine where the noise is actually coming from? Every vent, every other vent, and in any particular direction, then redirect it so it has no direct path to the talent's mics. This could be a drop shelf - I'm thinking a sheet of MDF, 2ft by 8ft, foam on the top, hung maybe a foot below the vents. Cheap to make, and you could even try it on mic stands to see if it works?
     
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  6. kmetal

    kmetal Kyle P. Gushue Well-Known Member

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    Boston, Massachusetts
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    sounds to me like its Mechanical Vibration thats the noise, not the air itself. thats why in studio design, we use isolation mounts, and insulated ducting to mitigate mechanical vibrations. air flow it best when its a big duct [volume] and low velocity [1-300 feet per minute]. so alot of air moving slowly.

    to be completely honest, im not sure how much you can do to mitigate this problem, without altering the ducts themselves. it seems like proper mic techniques, selection, and post production.

    it might be worth an inquiry to maintenance, to see how the system is zoned, maybe you could turn it off, or block the hole when recording without affecting anything else.

    right you get the direct sound, and all the echoes, and reverberation as the sound bounces around like ping pong balls, and lows move around like a shaking bowl of jello.

    your not getting a magnification as much as you are a canceling, and smearing of the initial sound, as it trails around the room.

    moving blankets on mic stands are a classic way to tame the mids and highs. lows need some corner trap, but shouldn't be much of an issue with dialog. its the low mids 200-500hz that will likely be an issue, creating a 'boxy or muddy' sound.

    i wish there was more that could be done in this situation, i really think it comes down to using the mic'ing to your advantage. you could maybe run an EQ on the way tot eh recorder so theres less to chop off later.
     

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