Friday, July 27, 2018

Conferencing and Room Acoustics by Charlie Crane

We’ve all been on that call.  The meeting participants on the other end of the call sound as if they are in a cavernous echo chamber making it nearly impossible to understand what’s being said.  Perhaps it’s a common complaint about a room that your company uses frequently.  One observation often made is that when normal conversations are held face to face in the problem room it doesn’t sound as bad. But, call in to a meeting in that room and the sound is terrible, requiring perfect concentration to participate in a meeting!  You’re not going crazy. Calling into a meeting in a noisy/reverberant room does indeed sound worse than conversing while physically being in the room.  There is a scientific reason why this is the case.

The field of inquiry of how humans perceive sound is call psychoacoustics, and nowhere are the effects of psychoacoustics more observable in day-to-day living than on video and audio conference calls. To listen and understand speech our brain’s audio processor performs many miraculous tasks behind the scenes as it were.

Spatial Cues

Our brains can detect the direction from which sound originates on the horizontal plane with an accuracy of 1.5 degrees. This is due to having two ears that are also on the horizontal plane.  The brain can detect astonishingly small differences in sound pressure level (sometimes called loudness or volume), time arrivals, and tonal differences between the sound entering our two ears.  Humans can only detect changes of 3 degrees in the vertical plane.  This is still pretty good for not having an ear on the top of our heads!

This amazing ability to detect where in space sound is originating helps spoken communication is several ways.  Firstly, when we’re in the room our brain differentiates between the desired speech energy and the noisy HVAC duct in the ceiling.  The brain considers the direction of the both sounds and then seemingly attenuates the HVAC noise through processing.  Secondly, this directional filtering also occurs when several conversations are occurring at once. Our brain can tune out the unwanted speech and focus on the important conversation.  This ability is referred to as the “Cocktail Party Effect”.  You’ve likely noticed this yourself; you’re at a party talking to a friend and unexpectedly you hear two people standing behind you say your name.  You are able to completely tune out your friend’s talking and eavesdrop on the other conversation even though your friend is right in front of you!  Lastly, in a reverberant room the brain focuses on the conversation based on direction and discounts the reverberance that comes from many/all directions.

No Spatial Cues! 

Now consider the conference call again.  The sound of the talker’s voice, the noise of the air conditioning, and the room’s excessive reverberation are all picked up by a table or hanging microphone.  These sounds are combined irrespective of spatial directionality into a new, hybrid signal.  Now, this noisy mix of intended and unintended sounds comes out of your cell phone, earpiece, or other VTC endpoint.  Unable to use your brain’s natural filtering processes, you hear a cacophony!

Knowing this when designing a conference space is critical to success.  In a way, the room must be acoustically quite good to sound acceptable on the far end.  If the room is only acceptable in person, it will sound poor on the far end.  Environmental noise reduction, the addition of acoustic absorption or diffusion, reducing the mic-to-mouth distance, and other techniques can turn a terrible meeting space into a winner.  Contact Adtech Systems today to review your meeting spaces, their acoustics, and the corrective technologies used within.

No comments:

Post a Comment

Conferencing and Room Acoustics by Charlie Crane

We’ve all been on that call.  The meeting participants on the other end of the call sound as if they are in a cavernous echo chamber making ...