How to record table conversations in noisy rooms
Voice Recording
Originally uploaded by clickcraftsman.
My research challenge at the Citizens' Parliament was to simultaneously record the conversations at 23 tables in close proximity, each with 6 or 7 participants. The room was so loud with everyone talking and poor acoustics that we had great trouble understanding each other.
I had no budget for this, so when I received quotations of up to $100,000 from audio production houses, I could only cry. But they are set up to deliver broadcast-quality sound, while we only need recordings that are clear enough to be manually transcribed to text for research purposes. And I didn't want twenty kilometres of wire strung through the room to a stack of mixers, either.
There are two parts to the problem: the device to store it in real-time, and the microphone to capture a single table conversation.
The price of portable digital voice recorders has fallen dramatically. I chose the Olympus model DS-40. It is a tiny device with 512mb of memory, enough for 17 hours of recording at sufficient quality. It records Windows media files and connects to PCs with a USB cable. Two AAA batteries run it continuously for 36 hours. It is dead easy to set up either by a configuration menu or the supplied software (Windows only). Street price is under US$100 in the USA and about AU$235 in Australia.
Each unit comes with a detachable stereo microphone which can be set at different sensitivities (lecture, conference, dictation). These are great microphones, but in a noisy environment they pick up everything.
The trick is to use what is called a boundary microphone. These are designed to sit flat on the table. They use the table as a sounding board to pick up the voices at the table at considerable gain over the noise coming from elsewhere. Crown makes the gold standard boundary microphones, but at high cost (see this PDF guide).
At a local electronics supply house I found a boundary microphone by Chinese manufacturer Yoga, denoted the model BM-26, at retail price AUD39.95. Unlike the pro-level mics, this model has a common 3.5 mm miniplug that fits into any portable recorder or laptop computer.
The improvement in audio quality was staggering! The background noise was still there, but the voices at the table were picked up much more distinctly.
The mics ran for about 20 hours in total over three days. Each mic uses an LR44 battery used in cameras or watches (cost ~$1.50). The mic draws minuscule current: the battery is only to "charge" the pick-up. The mic has an on/off switch, anyway.
This mic is unidirectional. I put it at the end of the table where nobody sits. It picks up speech around the table but not directly behind it (or the stage if that's the side you put it). I used it on oval tables almost two metres long and it picked up the voices around the table at relatively even volume--that's because it is most sensitive to the farthest voice coming directly in front of it.
The mic has a heavy metal housing. It has a full rubber foot so it doesn't pick up table vibrations. It can't be elbowed off the table.
The Yoga mic is monaural, so you can't identify speakers by their location at the table. In my limited experience of transcription, voice characteristics matter most in distinguishing speakers. But I could have used two mics, positioned slightly splayed from each other, and joined through a Y-adaptor.
I would highly recommend this solution to anybody who needs to record what was said at a meeting where everyone sits at the same table.
I just happen to be selling the recorders and mics on eBay :-)
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