Polycom, Polycom, Polycom
Uncategorized Posted Jan 13, 2015 by chenpr
In my series on everyday objects that inhabit our office, I cover the ever-dependable Polycom Sound Station: unsung hero of the conference call. Often taken for granted, the Polycom packs a lot of audio processing power. Using my knowledge as an amateur audio engineer and music producer I’ll try to unpack some of what is going on under the hood of that little black space boomerang in a way that is understandable to the layman so we might gain a greater appreciation for what is superficially just a speakerphone on steroids.
The two most basic elements of a Polycom are the same two elements of any phone, a speaker and a microphone. Where a Polycom differs is that it has a larger more powerful speaker and 3 cardioid (heart-shaped) microphones on each leg, giving it the ability pickup sound more sensitively over 360 degrees so you can be heard no matter what your position is relative to the device. This may seem self-explanatory, but the arrangement creates a few problems that if left unresolved would leave the device essentially useless.
The first issue is noise. And I don’t mean the kinds coming from your mouths that the device is meant to pick up; I’m talking about the ambient, environmental noise inherent in all rooms that most people don’t notice. This includes things like ventilation hum, computer fans, elbows and hands bumping the table, traffic outside and the natural reverberations of the room. Most people naturally tune these sounds out but more often than not they are much louder than we realize, so it is important that the Polycom filter out such aural clutter so that the conversation is easily understood.
It does this by first cutting out some of the audio frequencies that are not crucial for understanding human speech. The average human ear has a hearing range of between 20 hertz and 20,000 hertz (or20 kilohertz) but much of the sound on the lowest and highest ends of that range is way out of the range of what a human voice can produce. Many environmental noises are in those frequencies and add unwanted din to the sound being captured. In order to counteract this problem a Polycom equalizes the sound and only transmits those that fall between the range of 300 and 3300 hertz. This leaves only what is necessary to clearly understand speech, but is also part of the reason people can sound “tinny” or walkie-talkie-ish.
Another way the Polycom avoids environmental noise is through a process called gating. Gating only transmits audio when it is louder than a given threshold. So when the volume dips below the volume threshold—like when no one is speaking—sound ceases to be transmitted like the opening and closing of a “gate.” The Polycom also recognizes which of the three microphones are picking up the majority of the sound and will turn off microphones that are facing a direction where no person seems to be through a process called intelligent mixing. All this helps to eliminate unnecessary noise.
The second issue a Polycom must overcome is echo or feedback—the biggest problem inherent to all speakerphone technology. How does it do this? When the microphones start picking up sound from the speaker, you may start to hear the echo of your own voice on the call (which is distracting when trying to have a conversation). If the microphones are sensitive enough this echo could turn into a feedback loop that would create a loud screeching noise through the same process that creates feedback at rock concerts.
To avoid this problem, Polycoms process the audio transmitted to it and then subtract that signal from the microphone signal before it is sent out again. This process is echo cancellation. Explaining exactly how it does this without effecting the sound from the voices in the room would take too long for this blog post, but if you are a glutton for punishment look up the phenomenon known as phase cancellation or active noise control (ANC) to try and understand how this works. It is similar to the technique used in noise cancelling headphones.
These days almost any cell phone incorporates much of the same technology when used as a speakerphone and in that sense the Polycom isn’t exactly the most impressive device in the office, but when you realize all the engineering that goes into it maybe you’ll have a little more patience—and appreciation—the next time you dial into a conference call.