Dynamic range compression to fix audio levels of people talking in training meetings

Question

I know next to nothing about manipulating audio but I've recently started recording training meetings for my company. Some people have mics while others don't. The tool I've been given is the latest version of Adobe Audition. Is there a way for me to easily get all the people speaking at the same level so people don't have to constantly turn their volume up and down while watching?

Answer 1

<rant>
If you click on the first link in the PZM microphone page (the Bruce Bartlett one) take that with a pinch of salt - he clearly doesn't understand how they work in the slightest, and as a result most of what he says is either misleading or just plain wrong. And he's not the only one; if you look at the Media College link, they get it wrong too:
"A small condenser microphone is mounted face-down a short distance from the reflective boundary plate. This creates a pressure zone between the plate and the mic. The microphone detects changes in this pressure zone, rather than the conventional method of detecting changes in the surrounding air pressure (i.e. sound waves)."
The bit I bolded isn't really true, except in a very limited sense (this will have no bass response). The pressure zone is there regardless of whether the mic is or not. It's caused simply by the sound velocity wave having nowhere to go when it hits a physical boundary. At this point, the velocity wave (which is directional) hits the boundary where it becomes a pressure wave - and that's the non-directional part. If you put any microphone inside the pressure boundary (anywhere within about half an inch of it), you will achieve the same effect. So the other thing they got wrong was to describe a conventional mic as detecting changes in the surrounding air pressure, as such. The only mics that technically do this are true omnidirectional mics - but in the open air it's only local changes of pressure on the diaphragm (which are still directional) that occur, and signals arriving from different directions will still interfere with each other.
I'm not surprised that all these people get it wrong - they don't understand the basic physics involved, and it's not entirely intuitive.
If you want to find out how this effect works without purchasing a PZM/Boundary effect mic, it's quite simple. Get several people to talk in a relatively empty room, and you listen to them using headphones and a single mic. You'll have some difficulty hearing them all clearly. Then, while they are still talking, take the mic and place it somewhere between 1/4 and 1/2" from a wall. As you approach the wall, you'll end up with a load of cancellation effects, because sound waves hitting the wall will be bouncing off and cancelling out at different frequencies, according to exactly how far you are from it. But as you get within the magic pressure zone, everything will suddenly sound different, and much clearer (although a little quieter). This is because all of the competing sound waves don't cancel out any more. Now they aren't 'waves' as such, so they don't have a 'wavelength', but are simply pressure representations of them. You can't have two pressures out of phase in the same place (this is physically not possible!) so you don't get all the cancellations.
So with an omnidirectional mic in the pressure zone, you get a hemispherical response. Everybody says that you can get a more directional response using a more directional microphone, but in reality the differences are quite small if you use them on walls. The smaller the boundary, the less it intercepts long wavelengths (ie, bass), and that effect is quite significant, though.
So why did Bartlett, et al get it wrong? Because they never read further than the first section of Crown's Mic Memos. Bartlett is particularly culpable because he edited it!
If you scroll down far enough, you get to the magic paragraph, as follows:
"Ed Long and Ron Wickersham, in studying the behavior of flush-mounted microphones, uncovered a
basic error in our thinking. Within a few millimeters of a large surface, sound levels from a pair of
equal level signals add coherently because, in close proximity to the surface, the particles are still in
phase as they accelerate after being brought to a stop by the boundary. This creates what is called a
pressure field right at the surface of the boundary.
“A pressure field is one in which the instantaneous pressure is everywhere uniform. There is no
direction of propagation.”
The "basic error in their thinking" is the bit at the start that everybody else parrots. I'd have edited the document somewhat differently, I must say!
</rant>