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Audio Recording: Deploying a Recorder

by Steve Moon

Recording audio is the best way to find out what is happening in the woods when you are not there. You can leave a recorder in the woods and retrieve it a few hours or a few days later. Then you can either listen to the entire recording in real time or use a computer program like Audacity or Adobe Audition to analyze your sound file, which is much faster than listening. I will use Audacity in my discussion, because it’s the most commonly used, easy to learn, and free. More on working with those programs later. Here are some guidelines for capturing a recording using a small digital recorder.

A huge variety of small digital recorders are available, ranging in price from $40-$50 up to $500 or more. Most are under $300, and quite a few good ones are priced somewhere in between. Two brands that have proven to be good quality and durable are Olympus and Sony. Along with a recorder you should also use external stereo microphones (mics) that plug into your recorder and are powered by the recorder. External mics have many advantages over the internal mics built into all recorders. External mics are generally more sensitive. Because they are external to the recorder, the recorder can be protected by a waterproof container while the mics remain outside of the container or stick out of the container’s side. Two good sources for external mics are The Sound Professionals and Giant Squid Audio Labs. External mics cost around $75 for a stereo set, and can be purchased with the typical 5-foot cable on each mic, or a custom length. Single (mono) mics and stereo pairs of mics are available. Stereo mics are better because the recordings sound more natural and you can more easily tell when sounds are coming from more than one source or direction. Always make sure to purchase omnidirectional mics because they pick up sound from a wider area. Two stereo omnidirectional mics will allow you to record a more natural soundscape, similar to what you hear in real life.

Recorders are delicate instruments and are not waterproof. External mics are waterproof when used correctly. The key to making a pair of external mics waterproof is to point the mics slightly downward when deploying them. That way moisture drips away from the mic rather than into it. Mics come with clips for attaching them to objects such as small branches or the bark of a tree. If you are modifying a waterproof enclosure for your recorder, you can drill a hole for each mic, just big enough for the mic to poke out from the enclosure. Make sure the holes for each mic point slightly downward so that when your recorder is deployed the mics are waterproof. It’s that easy! I have field tested this method over several years and it works. More on building an enclosure later. Whatever recording system you use, here are some guidelines for deploying your recorder to obtain the best possible audio recordings:

Wildlife audio recording is controlled by the weather. Don’t bother recording in the rain. You cannot record good audio in a storm or steady rain.

Find a location that interests you. It may be in deep woods by a river or in your own backyard. If you have good visibility and can see for a few hundred feet in more than one direction, you have a good recording location. If the woods are real thick do the best you can to find an area with good visibility. If you can see well you will be able to record well. Good visibility means good recordings. The same objects that block your vision will also block sounds. Buildings, vehicles, thick bushes or trees can block sound. The higher off the ground your recorder is placed, the better you will be able to record distant sounds. Look for a spot that’s not low in the landscape. Small rises are often ideal. If you are deploying a recorder box on a tree make sure that it’s not a big tree, because the tree will block sound behind the recorder. Find a small tree so that the mics can pick up activity behind the tree. Do not use the foam wind screens that come with microphones! Foam windscreens cut down drastically on what you are able to hear. If a recording is noisy due to wind, you can filter that out easily using Audacity. Most recorders have a "low cut filter" which gets rid of most of the rumble from wind noise. If the wind is blowing when you set out a recorder, look for a "wind shadow." A wind shadow is an area where the prevailing wind is blocked by trees or a building. If you are ten feet or more away from a building you will be able to hear sounds in the entire area well. The closer you are to a building the more the sounds from behind the building are blocked. If the wind is strong, do the best you can to find a good location in a wind shadow. Walk around the area until you find a spot where the wind isn’t hitting your face as much as in other spots. Now you’re in the wind shadow. Deploy your recorder. Many sounds interfere with audio recording. There is the wind and the rain, but many other things as well. Some are impossible to avoid, such as crop harvesting and storage equipment. Combines and grain driers are a fact of life in some areas at certain times of the year, and when the harvest is underway they can go on all night. Jets and small aircraft flying overhead are also impossible to avoid, but those don’t last long. Small streams can be very noisy. Your recorder will amplify the sound of a stream, creating white noise that is hard to listen through. Move at least 50 feet away from any stream. The farther you are from a noisy stream the better. Most of us use cell phones, and they have some handy features that you can use when you set out a recorder. Turn on locational services so that when you take a photo the geographic coordinates for that location are recorded with the image file. Some phones will show the location where a photo was taken on a map. You can use a computer to find the geo coordinates in the photo details that are recorded with each photo. Enter those coordinates into a map or satellite image program such as Google Maps or Google Earth, and you will be able to use those programs to help you find your recorder. Take several photos of the recorder and the surrounding woods. Don’t use the first photo for referencing geo coordinates, because sometimes it takes a phone more than one image to find a true location. Send the third or fourth photo to yourself in an email while you are still with your recorder. Write "deployment - (location)” in the subject line. Describe the location and give any other relevant information in the message. Photos will help you find your recorder but if you are familiar with an area you will find it easily. The trick is to hide the recorder from other people. After hundreds of deployments I have never had a recorder stolen.

I have never locked one to a tree using a locking cable, but you can do that if you think it’s necessary. I clearly print my name and phone number on the outside of my recorder boxes, and always place two or three cards inside of each box with my contact information. On the outside of each box I also print this message: "Wildlife survey in progress. Please do not disturb. For information call ___-_____ and leave a message or text me. Thank you!" Most of the time I just sit my recorder on a tree branch or two where it won’t fall, and sometimes I use a cord to tie it securely to a small tree. When you retrieve your recorder leave the batteries and memory card in the recorder until you can transfer the audio files to at least two separate computer hard drives. Three is better. Label the folder containing all files related to the deployment with a standard that you should follow for all Bigfoot data file folders. YEAR, MONTH, DAY, PLACE, ADDITIONAL INFORMATION. Do it in this standard format and do not vary it in any way whatsoever: "2018.01.04 Skycastle Farm, extreme cold, etc." You will be so happy that you did this. Always do this immediately. When you are ready to analyze a file NEVER listen to the original file. Always make a WORKING COPY and mark it as such. Keep the original file in pristine condition. Keep track of how many hours you use a set of batteries. Write it on a piece of tape on the battery compartment door or back of the recorder. Designate "lith" for lithium batteries, or "alk" for alkaline. If you use rechargeable lithiums, get the highest mAr you can find. The mAr, or milliamperes hours, can range from 600 all the way up to 2600 or more. Get the highest number you can find. They cost more but they will power your recorder all night when you need it the most.

This 24 inch parabolic audio dish is custom fitted with an Earthworks microphone, and is intended for recording of very distant sounds. Testing is currently underway. A smaller 12 inch parabolic dish is used while walking about.

This recorder is the “full Monty”, with a 12 volt, 15 amp hour lithium rechargeable battery pack powering the audio recorder and a 9 volt microphone preamplifier which bypasses the internal amp of the audio recorder, custom power adapter harness, a low-pass filter that cuts out frequencies above 1,500 hz and a stereo omnidirectional microphone set with custom 12 inch cables, all in a waterproof case. This setup is perfect for recording in locations where insects and frogs are extremely noisy. Using a recorder that does timed daily recording, this setup allows for recording six hours a night for about thirty consecutive nights.

I have found that mounting a lightweight recorder on the brim of a straw hat with stereo microphones with 12 inch cables is an idea setup for walking about. I also use a baseball style cap with stereo mics clipped to the center button on top, and 5 foot cables looped around and through the Velcro closer on the back of the cap, leading to a pocketed audio recorder.


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