Audio Theory and Microphone Tuning
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. I am constantly challenged by the rooms delivered to our team that have excessive HVAC noise or imperfect room shapes that are not conducive to quality audio-conferencing communications. 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.
We start with “How does the room sound.” Not everyone understands audio is best adjusted and tuned utilizing the human ear not your eyes when it comes to adjustments. 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 the audio quality will suffer. EQ is a large concept of this, which is why this skill should be reinforced from the beginning. This also can be shown by looking at the big name mixing and mastering engineers. Bob Ludwig, who does mastering at Gateway Studios in Maine, is well known for what he does with the songs he is given. But he doesn’t give away any of the levels or settings he uses. Why? Because he knows if he gave out those levels, everyone would just copy and paste those levels. They would not be using their ears, they would just use the tools with their eyes. This would cause the tuning process to focus on the visual levels not how the environmental parameters impact the quality of sound.
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 coverage would work well over the whole divide/combine setup this system had. So, what tool did I use? My ears.
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 air-conditioning system installed was producing a high level of noise. My SPL meter had the noise hovering around 50-55 dB. In order to give people a reference, a conversation between two people hovers around 60-65 dB. This obviously would pose a problem to the quality of audio being represented to the far end of any audio or video call.
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 spectrum picture above shows a close example of what I was getting for noise in the room. I fired up a 3-band parametric EQ, and I started on the center frequency. From this point forward, it was up to my ears. 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 I made with this hurt the intelligibility of the person talking. Unfortunately, I was forced to compromise. I still had 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 if we want to adjust audio levels within a system, whether it be near end or far end. Second, the visual tools are a good starting place to work with audio, but not to be depended on. Lastly, sometimes we cannot fix everything with the quality of the audio. 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 continue to strive to improve the performance of our integrated technology solutions we provide to our customer.
Ryan Bennett – AV Technician, Audio Engineer – VisionPoint LLC