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Distance micing in a noisy environment #3011581 10/09/19 01:52 AM
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Mike Warren Offline OP
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I have been asked if it's possible to send a live audio feed from one room where 2 people are working into another room.

Sounds easy except...

1/ No mics allowed on the people. They are thinking of a couple of directional microphones placed about 2.5m away. The people don't move around much.
2/ There is a noisy machine in the room. I haven't heard it, but I understand it is a continuous noise like and air conditioner, but with a higher frequency whine component.

I've asked for a recording of the machine so I can at least get an idea of the spectrum.

The people in the second room need to clearly understand what's being said by the 2 people in the first room.

I'm told the SPL of the machine is around 56dB @ 1m

Anyone have any idea where to start on this?

Does anyone know if there's a DSP noise cancelling unit available that might help here? I'm thinking of feeding the directional mics into a mixer and then into the DSP along with a third omni mic.


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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011605 10/09/19 03:07 AM
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J. Dead Offline
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Shotgun mic?


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Distance micing in a noisy environment [Re: Mike Warren] #3011606 10/09/19 03:11 AM
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Shotgun mics could be a benefit if people stay put as you say. Maybe you can rent? Or have a friend who shoot video, shotgun mics are widely used for that.

Izotope makes a software called RX that is supposed to be excellent at removing noise. I've never used it.
Seems like reversing the phase of the noise would at least reduce it. Tricky because you don't want the mic that gets phase reversed close to the people speaking or it will cancel them too.
So it will already be out of phase, this could easily be done in a DAW after the fact but not live (at least that I know of).

Good luck


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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011610 10/09/19 03:23 AM
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Mike Warren Offline OP
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A couple of shotgun mics was what I was thinking. They don't work as well in an enclosed room, and they will still pick up the machine. I'm more after ideas about real-time processing of the audio. There are several NR programs available (I have several, including Izotope RX and they would solve this after the fact, but I need real-time, and preferably hardware based, although if the only way is with a computer i could probably do that.

Edit: This is for a permanent installation.

Last edited by Mike Warren; 10/09/19 03:24 AM.

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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011615 10/09/19 03:51 AM
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Then perhaps this might work?
It appears to contnuously adjust phase. It also appears to be analog.
It is real time, does the job on the spot.

https://www.radialeng.com/product/phazer

Instead of aligning the signal so it is in phase you would align it to be out of phase.

If one signal is the people speaking with the mechanical sound in the background and the other is just the mechanical noise it should be possible to adjust the volume and phase of the mechanical sound to cancel as much of the sound as possible.

I doubt it would be perfect but it could make a big difference. You could lock it in a box so people don't fiddle with it.


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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011621 10/09/19 04:25 AM
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If it's for permanent installation, can the machine be isolated -like the plexiglass cages they put around drum sets? What about other acoustic room treatments? If you can prevent reflections of the noise from other walls in the room, the shotgun mics will be more effective.


Dan

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Re: Distance micing in a noisy environment [Re: J. Dead] #3011622 10/09/19 04:43 AM
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Mike Warren Offline OP
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I should have made my original post more detailed, sorry.

The machine is a piece of medical equipment that is used in specialised operations and can't be enclosed. The whole room has to be sterile so I'm not allowed to apply any acoustic treatment. The room has sound-reflective walls, which is why shotgun mics won't do a great job. It's a problem that I don't believe analog processing will be all that effective with. I'm hoping there is a DSP based device available that can do a better job of noise cancellation than a phase shifter. Or perhaps another idea I haven't thought of.


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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011629 10/09/19 06:32 AM
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If you didn't have to stream audio in real time, it would be a lot easier. A restoration tool like RX7 would likely be effective for after-the-fact processing.

Why are no mics allowed on the people? There are necklace mics that would probably be ideal. The mics couldn't fall off, as could happen with lavalier or headset mics.. If the concern is wires, it could be done wirelessly. The dpa 4561 has been discontinued, but it can't be the only type around...and it was discontinued fairly recently, so I doubt it would be too hard to find if that could be at all suitable.

Since the people don't move around much, maybe a shotgun mic pointed down from the ceiling could work?

Re: Distance micing in a noisy environment [Re: Mike Warren] #3011639 10/09/19 10:12 AM
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Shotgun mics don't have "reach" but rather, have greater off-axis rejection than the conventional patterns, though it's in "lobes", with sharp nulls in some directions and not-so-nulls in other directions. The trick of using a shotgun mic is to point it in the direction where the noise pickup is tolerable and try to get the talent within range of the main (straight ahead) lobe.

Have you thought about a mic with a parabolic reflector? That's what they used to use for broadcasting football games before they put wireless mics on everyone. Another thought is that there are a couple of companies who have been working to build highly directional and steerable mic arrays. Sennheiser is one. Come to the AES show next week and see who's got what you might be able to use.

The fact that the machine has a recognizable noise spectrum means that it's a perfect candidate for the kinds of software noise reduction that are pretty popular today. What you really need to do is try to snag an iZotope ANR-B, a live noise reduction processor that was introduced about 10 years ago. It didn't last very long in the marketplace, probably because it cost about $5,000, and iZotope was already competing with themselves on price with their RX software. But if you can find one, that would do the trick. It's the medical biz, so price should be no object.









Re: Distance micing in a noisy environment [Re: Anderton] #3011640 10/09/19 10:15 AM
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Originally Posted by Anderton

Why are no mics allowed on the people?


Sterile operating room environment, I guess. There are a number of tiny on-actor mics that are moisture (sweat) resistant, but it would take an SM-57 to survive a run through an autoclave. wink

Re: Distance micing in a noisy environment [Re: Mike Warren] #3011642 10/09/19 11:39 AM
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Can you just tell us exactly what you're trying to do? I feel like we're just blindly throwing darts at a board. Right now I am envisioning trying to record from across an auditorium 2 doctors doing brain surgery next to a copy machine.


Dan

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Re: Distance micing in a noisy environment [Re: Mike Warren] #3011660 10/09/19 04:04 PM
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Here you go. Probably will solve your problem:

https://www.ebay.com/itm/133064021410

A used iZotope ANR-B for under 2 grand. If I was still doing outdoor field recording, I'd probably snap this one up myself.

Re: Distance micing in a noisy environment [Re: Mike Warren] #3011785 10/10/19 12:11 PM
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I also imagine it is an operating environment where things directly over the operating field need to be sterile. But frankly a lot of things aren’t. Not sure why the main actors couldn’t have a clip on mic underneath their sterile gowns patched wirelessly to the receiver. The mics would not have to be sterilized. You would probably have some noise from movement, but it would increase the vocal volume to the machine noise. I haven’t done the actual mic placement, but I did travel on the handle side of the knife for 30 years. Cheers!

Re: Distance micing in a noisy environment [Re: Anderton] #3011919 10/11/19 07:26 AM
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Mike Warren Offline OP
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Originally Posted by Anderton
If you didn't have to stream audio in real time, it would be a lot easier. A restoration tool like RX7 would likely be effective for after-the-fact processing.

Why are no mics allowed on the people?


I don't know. That was my first suggestion when my boss put this to me. He says the doctor has specifically said he does not want to have anything attached and even specified where the mics must be mounted; 2.5m from the people operating.


Quote
Since the people don't move around much, maybe a shotgun mic pointed down from the ceiling could work?


In my experience shotgun mics tend to still pick up a lot of background noise when used in a enclosed space. I expect I'll need to use shotgun mics, but I'll also need some sort of noise cancellation.

I've asked for a recording of the machine, but am off work for a week or so to recover from an accident.


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Re: Distance micing in a noisy environment [Re: J. Dead] #3011920 10/11/19 07:31 AM
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Mike Warren Offline OP
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Originally Posted by J. Dead
Can you just tell us exactly what you're trying to do? I feel like we're just blindly throwing darts at a board. Right now I am envisioning trying to record from across an auditorium 2 doctors doing brain surgery next to a copy machine.


I don't now any more than I've told you. The machine is a medical device of some sort that is used during the operations.

The reason for my post was mostly in the hope someone knew of a DSP based real-time noise canceller that could be used. The iZotope ANR-B looks like it could be quite suitable. Unfortunately, that doesn't seem to be a current product so would not come with a warranty or support. Also, that one on eBay does not ship to Australia.


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