Audio Theory and Microphone Tuning
Updated May 22, 2020
Why Applying Audio Theory to your Installations Improves Conference Room Performance
As a technical representative, I focus on the challenges provided by the original design that I will inevitably face when it’s time for system installation. System performance at the end of the day is primarily affected by the room acoustics. Rooms delivered to our team that have excessive HVAC noise or imperfect room shapes may not be conducive to high quality audio-conferencing communications; these rooms prove to be a constant challenge. After connecting the system as designed during the configuration phase, we check levels on a series of test calls with video and bridge call environments. Sometimes engineers have specified ceiling microphone arrays, and it is up to the technical staff left behind to solve the inherent noise factors of the space. I have been tasked with developing a measurable approach to overcome these factors utilizing the science of audio as it relates to adjusting the parameters of the digital signal processor to filter noises that are constant to provide the level of quality in the audio performance clients have come to expect.
How Does the Room Sound?
Not everyone understands audio is best adjusted and tuned utilizing the human ear. The phrase is best said as “Mix with your ears, not your eyes”. When working in a studio, this means adjusting levels for an instrument or vocal, and using our ears to perceive what changes we are making. The graphs say one thing, but if they are relied upon too much, audio quality will suffer. EQ plays a major role in this concept, which is why EQ should be introduced in the beginning. This concept is best represented by analyzing the approach practiced by big name mixing and mastering engineers. Bob Ludwig, who is a world renowned mastering engineer at Gateway Studios in Maine, is well known for his EQ approach to mastering songs for Grammy nominated artists. But he doesn’t publicly share any of EQ parameters, techniques, or compression settings he uses. Why? Because he knows if he shared them, many engineers may copy and paste his settings for situations where they might not make sense.
That “mix with your ears, not with your eyes” concept can also be used when we are using EQ within an AV system. Since almost all signals are digital at this point, we can get really close and specific on the aspects of sound that we want to manipulate. This is where I started with the most recent project I was involved in. The system utilized 4 of the new Shure MX 910 ceiling array microphones. I knew how to configure the microphone patterns, but I wanted to make sure the polar pattern coverage would compliment the divide/combine setup this system had.
So what tool did I use?
I set up a separate analysis system using an audio interface wired into a direct out of the digital signal processor. I placed a few external microphones within the space to get a feel for the noise levels of the space. The first thing I noticed was the A/C system, which was producing a high level of noise. Our SPL meter indicated that the noise levels were fluctuating between 50-55 dB. To understand how noisy that is, a conversation between two people ranges 60-65 dB. See how this could be problematic?
This can pose various quality issues when the furthest user at the far end of the room is speaking.
Usually this is not a huge problem, but in this case the levels were so loud that it was impacting the intelligibility of the people in the room significantly. It was a bad combo of a loud A/C system with ceiling microphones. Adjusting gain just turns up everything, so where was my next attack point? Equalization. Now, I did mention that we should mix with our ears, not our eyes. But this does not mean that we can’t use these tools to help us fix what we are looking for.
The above graph represents noise levels in the room. I fired up a 3-band parametric EQ, and I started with the center frequency. By adjusting the center frequency, the gain reduction, and the bandwidth of the EQ, I was able to eliminate most of the rumbling low frequencies. From there, I tried hitting the next area of interference. However, any gain reduction may reduce the intelligibility of the person speaking. In this case I was forced to compromise. There was still some low rumble in my mix, so I added a low shelf filter to help with this even more. A male voice may not resonate as deeply with these mics as they could have before, but I doubt the far end would hear it over the air-conditioning system noise anyway.
What can we take away from this?
First, we should use our ears when adjusting audio levels, whether it be near end or far end.
Secondly, visual tools are a good starting point when it comes to audio, but not they shouldn’t be depended on.
Third, sometimes we cannot fix everything when it comes to audio quality. Equalization can only go so far, and cannot fix everything. There are some things that are just out of our control, such as excessive room noise, outside noise interference and reverberation in spaces with hard surfaces.
Ultimately, the knowledge of the technical staff and the tools they have at their disposal certainly will help to create exceptional customer experiences with the audio technology installed with not so exceptional acoustically proper spaces. VisionPoint is committed to the education and tools required to improve the performance of our integrated technology solutions we provide to our customers.
— Ryan Bennett – AV Technician, Audio Engineer – VisionPoint LLC