A site dedicated to the review and analysis of potential sasquatch vocalizations, Sasquatch Bioacoustic combines techniques from the domains of intelligence collection, audio analysis and bioacoustic studies to examine the evidence of sasquatch through their vocalizations. ~Monongahela

Thursday, July 28, 2011

Building a Long Duration Recorder

I've long sought to piece together an audio recorder capable of running unattended,for weeks on end, in remote forest locations. While it has been possible to put such a rig together for some time, it was always a costly affair. It wasn't until recently that all the right products became available, off the shelf, and for a price that wouldn't break the bank. I recently assembled a field recorder for under $200 that operated for 43 days in the field, recording 290 hours of audio (10 hours per day for 29 days, until the memory was filled). For the record, here's how I did it...

Key to the system is an affordable, effective, and configurable audio recorder that can be powered from an external power source. I found just such a device in the TASCAM DR-03 for about $79.

The DR-03 includes firm-ware that allows it to be configured to start recording at one time, and stop recording at another time (impossible to find in other affordable recorders, but maybe not so in the future). It also accepts micro SDHC memory cards where it stores the recorded audio, so increasing the amount of storage is a factor of how much you want to spend. Finally, the recorder comes with a USB port which can be used to power it, from an external source (AC or DC).

So with the recorder in hand, I needed a good battery to power it from. I found a great solution at Walmart in a deep-cycle 12 volt marine battery with 105 amp-hours of power (more amp-hours means more recording time in the field). It was nicely priced at about $65. Also in the automotive section at Walmart I found a battery clip extension that clips to the battery's terminals and provides a cigarette lighter-type power socket ($6)

In the same area I looked for and found a 12 volt dc to usb adapter ($7).

And finally, in the camping section, I found a tough plastic storage bin to house everything and protect it all from the elements ($20).

The last thing I purchased was a 16GB mini memory card for $35 from Microcenter. All together I have $187 in the materials for this device (I got the recorder on sale for $49).

Putting the thing together was straight forward. Not necessary, but highly recommended, I added a pair of external mics that I already owned ($75 from Giant Squid Audio Labs - ).

I started by installing the 16GB memory card into the DR-03 recorder. I then powered up and configured the recorders timer function to begin recording at 8 p.m. each evening, and to cease recording at 6 a.m. each morning.

Next I charged up the 12 volt battery to ensure it was topped off before I put it out in the field. I placed the battery in the storage bin and added padding around it so it would not shift while in transit. I drilled a couple of small holes under the handles of the bin where the microphones could poke out, but receive protection from rainfall by the handles above them.

I connected the audio recorder to the DC-USB adapter with the USB cable that came with the recorder. I then plugged the DC-USB adapter into the DC socket on the 12 volt battery clip extension. I connected the battery clips to the terminals on the 12 volt battery, and voila, the recorder powered up.

I plugged my external stereo mics into the audio recorder and then pushed the mics out through the tightly fitted holes I drilled under the bin's handles. I used small strips of duct tape to secure all of the connections and equipment in place. Mics were taped to the bin. Plugs were taped into sockets. Even the clips were taped to the battery. I didn't want anything to shake loose easily, should something upset the box while it was in the field (short of turning the whole thing upside down).

Finally I placed the recorder inside a gallon-sized zip lock bag to protect it from direct precipitation. I did the same with the USB-DC adapter for good measure. And then I taped both securely to the inside of the bin's hinged lid. I closed the bin, which is equipped with a latch for a padlock, and used stout wire to secure the lid closed.

And that's exactly how it sat, deployed to the field for 43 days, recording 10 hours every night (for 29 nights).

Since that deployment I've learned a few things that will help me improve the system, or build a second one for less cost.

First, the recorder does not need to stay powered on, as I had left it. It can be turned off and the automatic record function will power up the recorder at the proper time and begin recording. It will also power the recorder down after recording is complete. This feature will save a lot of power and allow me to get by with a much smaller battery and storage bin (Walmart has a 12 volt lawn mower battery for $20 that should power the recorder for a month).

Second, maxing out the mic sensitivity might cause some recording problems. In my first field test there are segments, especially during noisy parts of the recording, where interference obscures the recording. This may be a result of turning mic sensitivity up to max.

I'll build a second version of this field recorder and test the onboard mics for their sensitivity. If the prove good enough then I may leave the external mics out of the build and just go with what the recorder has built in. It will present a challenge when trying expose the mics from the case to gather sound, but still protect the recorder from precipitation. But I think it can be managed. Either way, the next version of the recorder should be smaller, lighter, and easier to pack out into the field.