Recording in a room with reflections

egproductions

egproductions

Veteran
On occasion I'm "forced" to film in a room with, shall we say, less than ideal acoustic attributes. Sound treating, mic selection/placement, and post processing solutions aside...I was wondering if telling the talent to soften their delivery actually helps in reflections or if me needing to raise the gain to compensate for speaking softer will negate any reverberations that were reduced?
 
It could help some. Worth a try as long as the mic is close. The speaker is the source so lowering the output would in theory lessen the strength of the reverberations to make it back to the mic. Never tested so I am kind of guessing so please let us know if you have a chance to test.
 
It should make things worse. The signal to noise ratio of the voice going directly to the mic and any reflections remains the same regardless of how loud they are speaking. But a weaker voice forces you to turn up the gain, which will raise the level of the room sounds in relation to the person speaking and also increase the amplifier noise.
 
It can help in very large rooms, like gymnasiums and such if the talent speaks lower. However, I can only recall one instance, where I asked an actor to speak in a lower volume to avoid 'exciting the room'.
 
I would assume you are using a hypercardioid or supercardioid and NOT a shotgun? Also, there are some surprisingly good De-Reverb tools now, it's not nearly as big of a deal as it used to be. The plug-ins won't make it perfect but they can make it usable.
 
I carry sound blankets which while not a perfect solution, helps to make things a little more acceptable.

Especially helpful in sit-down interviews. Placing them on a reflective floor, and on C-stands just off camera.
 
Paul F said:
It should make things worse. The signal to noise ratio of the voice going directly to the mic and any reflections remains the same regardless of how loud they are speaking. But a weaker voice forces you to turn up the gain, which will raise the level of the room sounds in relation to the person speaking and also increase the amplifier noise.
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EXACTLY.

Tell them to speak LOUDER, and then DROP the gains, and that should help minimize the reflections. Get the mic as close as possible, which will let you turn the gains down lower, and that will increase the signal to noise.
 
Yes, getting the mic close and sound blankets of course would minimize reflections being picked up. In theory David and Barry’s explanation makes a lot of sense, however there is something naggining at me that makes me think if I told the talent to talk lower instead of project, the reflections would be minimized. I can’t even hypothesis a reason why this would be true but I still have this naggining feeling like their voice wouldnt “reach” the hard surfaces as easily even though it doesnt logically make sense as far as I can tell.
 
Yes test for us and settle the question. There are two ideas being discussed here, signal to noise ratio and reverberation. I think your original post was about reverberation more than signal to noise
 
My intuition thinks along the same lines as you egg, but my nerd side thinks it's as I said.

I have to talk it through to see if I can predict your results. Let's see if I have this right. Someone says a word and it has, let's say, 12" to reach the mic at some sound level. That same word travels on towards a wall 8' away. The sound pressure level drops by half as you double the distance (1/r^2). So when it hits the wall, it is 1/8 as loud as it is at the microphone. If we assume the wall is a perfect reflector, then the sound goes back to the microphone and hits it at 1/64th of the level the the direct sound hits it. It doesn't matter what the sound pressure level is, this is the physics of the problem. Loud or quiet, the sound will always be 1/64 as loud. The wall will present some attenuation, but that attenuation will be the same for any sound pressure level.

What happens at the microphone? Will a lower sound pressure level result in a less than proportional signal from the microphone? I haven't been able to find anything about this. In other words, a microphone puts out so many millivolts for a given sound pressure level. But is that linear over the a range of sound pressure levels or will the microphone actually provide more attenuation to a quieter sound and give you the results your are looking for? Anyone?

Regardless of all of this, you still have the problem that you will have to turn up the gain which will make room tone louder and amplifier noise louder.
 
I was in the worst possible version of this, an empty water tank the size of a football field. Speaking quiet may help. In my case a "normal volume" "anything" had about a 2 min decay. I was recording FX, dialog would have been impossible. It's an energy thing. You can not over power the situation, but you may underpower it. The power drops by the square of the distance so if you close mic and they are quieter... Maybe. It's kind of a "no win" situation. "Noise" is possible to remove in post but reverb... Not really. There are tools out there but really maybe a 10% reduction at best.
 
It's not reverberation vs. signal-to-noise... reverberation IS noise in this scenario.

Do you guys not remember when I posted this as a test? We had an echo chamber of a garage to shoot in, and DJ and I did test recordings. With the mic at what some folks would consider a "normal" distance, the place sounded like a literal echo chamber. We put up sound blankets all around and tried again, and the situation was almost exactly the same. We took the sound blankets down and moved the mic very close, and the echo disappeared almost entirely.

Sound dissipates in energy over distance, even if it bounces off hard surfaces. If you can get the gains low enough, the echo will fall off. Compensate by moving the mic as close as possible. Get the strongest signal you can, and then drop the gains accordingly to crush down the noise (echo).
 
Yes, the close mic is the answer but that is also proving the sound pressure level drops by half as you double the distance (1/r^2) rule. Barry, you fixed the problem by reducing the comparative distance between the mic and the walls. This allowed you to win the ratio. I agree the increase of the mic gain will make the mic more sensitive therefore pick up the lower volume reverberations.

But, there is another factor which could help - post processing. What if you lowered the talent's voice but did not increase the mic gain? Then in post selectively EQ boosted the talent's voice along with compression and some noise/de-reverb tools. This *might* result in a less reverby recording...
 
Bassman2003 said:
Yes, the close mic is the answer but that is also proving the sound pressure level drops by half as you double the distance (1/r^2) rule.
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You got the formula right but that isn't double the distance it's the square of the distance, drops off a lot faster.

But, there is another factor which could help - post processing. What if you lowered the talent's voice but did not increase the mic gain? Then in post selectively EQ boosted the talent's voice along with compression and some noise/de-reverb tools. This *might* result in a less reverby recording...
Click to expand...

As someone with almost 30 years in sound post I would not recommend trying that route. EQ isn't going to get you very far and echo removal tools are extremely limited. The main issue boils down to what you are trying to get rid of is essentially just a delayed version of what you are trying to keep. There may one day be a complex AI tool that can differentiate the two but there isn't anything now (at least that will run on any system you have access to, NSA might have something?). Noise reduction won't work for the same reason, what you want is very close to what you don't, and they are mixed on top of eachother.

Putting less energy into the space is about the only way to cut down on the echo's and getting the mic as close as possible will reduce the relative volume of the echo's.
 
A small change in blocking may also help, especially with curved walls. Move them out of the focus point and things change fast.
 
Thanks for the test. Imho, the very first test with the omni did put the focus more on your voice and less on the room. Although the performance might not be acceptable as it is so different from normal speaking. The rest of the tests were as predicted with the room playing too much of a part.

So even if you could improve the situation from an audio perspective, the end result would probably not work from a project perspective.

Things to take away: Scout your locations. Lobby for good rooms. Treat the room if you can.
 
Bassman2003 said:
But, there is another factor which could help - post processing. What if you lowered the talent's voice but did not increase the mic gain? Then in post selectively EQ boosted the talent's voice along with compression and some noise/de-reverb tools. This *might* result in a less reverby recording...
Click to expand...

I would view this as an emergency fix and not a recording strategy. "Fixing it in post" is not a recipe for success ordinarily. And for non-professional interviews, asking them to change their normal speaking voice is pretty risky as well.
 
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