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How would you set microphones for a teleconference? This is real sound engineering in practice.

Yes we would all like to work in music, but there is a whole wide world of audio outside - with proper jobs and pensions!

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It's easy to fall into the trap of thinking that audio is all about music. But if I said that there are many more microphones used for speech than there are for musical purposes, I doubt very much that I would be wrong. Taking into consideration television, radio and communications, it's mostly about people talking to the masses, or with each other, and not singing or playing musical instruments.

For many audio enthusiasts who record music, the audio side of things comes first, and music comes second. This is good news because there are proper careers in audio outside of music. Yes there are proper careers in music too, but since so much music is now made in private studios, employment opportunities are fewer than there used to be, and opportunies were few back then.

My thoughts today were prompted by an article in AV Technology Europe magazine by Justin O'Connor about microphones for conference rooms. It is worth saying at this point that the term 'conference' today is likely to include the meaning and implication of 'teleconference' where it is expected that any conference should be able to accommodate remote participation almost as easily as if the remote delegates just walked into the room. (I'll add that I'm thinking about a boardroom table setting, rather than the type of conference with an audience, which would have additional areas of concern.)

So a remote participant in a conference would expect to...

  • See the room through a video link
  • Be seen by the participants in the room via a video link in the opposite direction
  • Hear everything that is said in the room clearly
  • Be heard clearly throughout the room.

One of these is more difficult than the others. To save you the trouble of guessing I'll tell you that it is to hear everything that is said in the room clearly. All of the others just need the equipment setting up properly. But to hear everything clearly requires in addition a good understanding of sound and sound engineering principles.

Acoustics

Firstly there is the issue of room acoustics. Remembering that the conference room is a business area, not a studio or entertainment venue, it is important that acoustics are given consideration to as significant a degree as the decor and selection of furniture. As in other areas of industry, sound is often treated as an afterthought, or given hardly any thought at all. So it wouldn't be unreasonable to expect a conference room to look great in all respects, and sound dreadful. This needs to be properly thought through right from the start.

As is often the case, large, hard, flat surfaces are problematical. Hard, flat surfaces reflect sound like a mirror reflects light. Sound from one end of the room will bounce back from the other. In a room 10 meters long, the reflection from one end of the room to the other and back again will take around 50 milliseconds or so, depending on the position of the person speaking (and of course temperature and humidity). 50 milliseconds is getting into the zone where syllables of direct speech will overlap with the syllables of the reflection, making intelligibility difficult. The human ear is pretty good at accommodating these problems, but microphones are not. So although the conference participants in the room may be able to understand every word that is said, any remote participants will have more difficulty.

My example above considers only one reflection, but of course there will be many, and the more hard, flat surfaces there are and the wider the area they cover, the worse the problem will be. The simple solution, as is pointed out in the article, is to use soft surfaces such as drapes and carpet rather than bare walls and wood or laminate flooring. The article also points out, which is appropriate in context, that art on canvas is a useful sound absorber. Photographs or art behind glass - well, that's another hard flat surface to cause problems.

Remember though that this is a conference room. It isn't a studio, so any measures that are taken to improve the acoustics should be appropriate for that kind of business environment.

Microphones

The article in AV Technology Europe has a lot more to cover, but I would like to summarize one point here that is appropriate for many audio applications. A microphone will pick up both direct and reflected sound. The further away the microphone is from the sound source, the greater the proportion of reflected sound there will be. This may be OK if you are recording a violin in a concert hall and want it to sound as such. But when intelligibility of speech is the main criterion, the microphone should be placed close to the sound source - the speaker's mouth.

So in a conference room, one microphone to cover the whole room would not work well. It might be OK for the people it is closest to, but not for people further away. The ideal is to use directional microphones, one microphone per person, each microphone just a few inches ( 1 inch = 2.54 cm) from the person's mouth.

To quote from the article...

Getting the microphones wrong will absolutely cause problems that cannot be mitigated later in the signal path.

Of course there is a lot more to the audio science of conferencing, but acoustics, microphone type and microphone positioning are the basics, and the basics of anything will get you a long way towards good solutions (look up beamforming microphones if you want to go further). And to go back to my point at the beginning of this article, audio for conferencing is a whole career path in its own right. And you might even get a pension at the end of it!

By David Mellor Wednesday September 20, 2017
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