8 Replies Latest reply: Mar 21, 2012 4:31 AM by SteveG(AudioMasters) RSS

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

    Kurt Perry

      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?

        • 1. Re: Dynamic range compression to fix audio levels of people talking in training meetings
          Bob Howes Community Member

          Well, you can use dynamics processing to even out levels but, depending on the differences between the voices (and some with mics, others without sounds pretty drastic) you may not be happy with the results.

           

          You'll find the effect you want under Effects/Amplitude and Compression/Dynamics processing.  I'm afraid it's not the sort of thing where you can just call up a preset and have it work first time.  You'll have to set the various parameters to control the threshold and ratio of the effect to get the best results.

           

          For quick and dirty, that might work.  However the other thing to consider is manually adjusting levels on the fly.  Using volume envelopes you can tweak levels by ear to tailor each individual part to sound as good as possible.  It sounds time consuming but, once you get your hand in, you can probably do the whole training session faster than in real time.

          • 2. Re: Dynamic range compression to fix audio levels of people talking in training meetings
            ryclark Community Member

            For even quicker and dirtier you could try the Effects/Amplitude and Compression/Speech Volume Leveler. But may turn out not to sound very nice.

            • 3. Re: Dynamic range compression to fix audio levels of people talking in training meetings
              SteveG(AudioMasters) Community Member

              It's not going to sound very nice whatever you do!

               

              In future the OP might be better off using more appropriate technology. The thing that immediately springs to mind here (and it can work pretty well) is to use pressure-zone mics spread around a bit - you pick up more from room contributions, and the clarity is far better, simply by virtue of how they work.

              • 5. Re: Dynamic range compression to fix audio levels of people talking in training meetings
                SteveG(AudioMasters) Community Member

                <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>

                • 6. Re: Dynamic range compression to fix audio levels of people talking in training meetings
                  Kurt Perry Community Member

                  I ended up going with the speech leveler in combination with the noise removal tool. It made the people with mics sound a little worse but it made the people without mics sound much better. Relatively speaking of course. I knew that there was no way to make this sound very good but I felt, in this case, it was more important to make it so people watching wouldn't have to constantly ajust their volume control.

                   

                  These trainings I record are at a different location each month and, USUALLY, only one person does any real talking and I can manually tweek the rare instances when an audience member is speaking. This is the first time it's been a real issue. Which is a good thing because I know I don't have the option of getting more equipment than what I have to work with: two wireless mics and a shotgun mic that I mount to the camera. (At least not any time soon.)

                   

                  It seems it's going to take some work to translate what people are telling me about using gates and thresholds into what the settings in Audition have. For example, the gate setting only went as low as -9db and the threshold setting, instead of going from something like -40db to 40db like I'd expect, went from 0 to 25. What the heck does that even mean? But I'll have time to figure that out. In the mean time, the speach leveler was a quick and dirty fix.

                  • 7. Re: Dynamic range compression to fix audio levels of people talking in training meetings
                    Bob Howes Community Member

                    Hmmm. 

                     

                    Bruce Bartlett may not understand the theory behind PZMs but he designs good ones.  He's responsible for the Crown PCC160 and now the Bartlett TM125, both of which are workhorses in the theatre industry..

                     

                    I have to suspect it's more a case of just trying to over simplify than truly not understanding, otherwise he got very lucky in the efficacy of his designs!.

                    • 8. Re: Dynamic range compression to fix audio levels of people talking in training meetings
                      SteveG(AudioMasters) Community Member

                      Bob Howes wrote:

                       

                      Bruce Bartlett may not understand the theory behind PZMs but he designs good ones.  He's responsible for the Crown PCC160 and now the Bartlett TM125, both of which are workhorses in the theatre industry..

                       

                      I have to suspect it's more a case of just trying to over simplify than truly not understanding, otherwise he got very lucky in the efficacy of his designs!.

                      No, he got lucky and employed the right people - he doesn't design them himself. Long and Wickersham, who invented the concept (not the mics) in 1978 misundertood what they'd done - it wasn't until the design was formalised by Wahrenbrock and presented to Crown as a manufacturing possibility that any real understanding came about.

                       

                      And they are seriously easy to 'design' once you've understood physically what you have to do. The only reason that there weren't loads more early on is that the fundamentals were patented by Crown - and do you blame them? You can even get around the stated limitation of needing a very small diameter capsule without any real difficulty if you want, although I wouldn't go beyond a half-inch one myself. I built one as an experiment circa 1980 and it works better than I ever thought it would. I made it out of an existing lapel mic and some wood...

                       

                      Steve's_PZM.jpg

                       

                      32 years old, and it worked fine last time I tried it - not that long ago. Couldn't call it a Pressure Zone mic, because they'd trade-marked the name by then. Notice the very fine grain in the wood - if I was selling them, I'd say that it improves the warmth of the sound!