Review: The AudioMoth USB Microphone from Open Acoustic Devices

This is a review of the new (yet-to-be available) AudioMoth USB Microphone designed by Open Acoustic Devices.

It is not currently available to the public (at the time of this writing). I must say that I feel privileged and honoured to be the first to get one. I’ve been fortunate to be able to test, review, and publish my thoughts on this brand-new USB Mic.

This very small unit arrives in an appropriately sized box.

(AA-sized battery for scale)

The size, is very small - Specifically: 35mm x 40mm. The weight, is very light!

Unboxing / AA size battery shown for scale 

The price of this unit, has not been officially announced. However, I’m told it will be under $100 US. Based solely on the fact that this small, versatile unit works very well across multiple software applications, I have a feeling it will be quite popular.

Clever business card!

As seen in photos, this unique unit has a green hard plastic outer casing. If you are familiar with some of the documentation provided by Open Acoustic Resources, you will have seen a photo of the Mic in both green and dark blue plastic cases. 

 Page 4 of 4, of the documentation mentioned above.

At this point I cannot confirm whether or not the unit will be available in dark blue, when it is released/available for public purchase.

Back view of AudioMoth USB Mic

From the outside/back view — you can see the area for the Micro USB connector, and a female 3.5 mm jack for plugging in an additional microphone. Or, as mentioned in their documentation "...a hydrophone" 

Thanks! That's all it took to get me thinking about my (unbuilt) DIY hydrophones... 

Having this additional 3.5 mm jack provides a great resource/platform for experimenting with additional microphones - Such as others you have on hand; mini-shotgun microphones, shotgun microphones, and DIY microphone projects.

When a microphone is plugged into the 3.5mm jack, the AudioMoth USB microphone is (temporarily) disabled. 

Inside is a perfectly (snugly) fitted, small circuit board.

Where the magic happens.

 

It's worth mentioning, that this AudioMoth USB Mic is a modified version of the original AudioMoth - With: the battery holder, 256KB SRAM, SD card holder, and real-time clock crystal removed.

I found both the external and internal design to be very well done - it also didn't take long at all before I became very pleased with it's ease of use, and it's general performance.

For a very quick start:

• Download the free AudioMoth Live App - from the Open Acoustic Devices Website.
• Out of the box - simply plug in a mini USB cable to the Mic itself, with the other end plugged into a laptop.
• Launch software - Click the green play button - this begins the spectrum display scrolling from right to left.

I would strongly recommend printing out the documents which you find of most interest, to have to hand for quick-reference. However, for the sake of being thorough - here are the functions behind the switch settings of The AudioMoth USB Mic:

USB/OFF: When the switch is set to USB/OFF the sample rates, gain and filter options can be set through the AudioMoth USB Microphone App above. The green LED will light when USB is connected.

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DEFAULT: When the switch is set to DEFAULT the device will enumerate as a USB microphone implementing the set sample rate and gain. The green LED will flash at a rate determined by the sample rate (identical to that of the standard AudioMoth firmware).

​

CUSTOM: When the switch is set to CUSTOM the device will again enumerate as a USB microphone implementing the sample rate and gain settings as above, and also the requested filter and advanced settings. The red LED will flash at a rate determined by the sample rate (identical to that of the standard AudioMoth firmware). You can switch between DEFAULT and CUSTOM whilst recording to see the effect of these settings.

I generally keep mine in 'Default' mode, for the majority of my recording.

The (proposed) relatively low cost of this USB Microphone will make it an attractive bit of kit for many people. Not just those involved in ultrasound recording (bats!), but those involved in wildlife sound recording in general.

Since it not only excels at recording ultrasonic sounds—it also does a good job of recording audible sounds as well.

Here is just one of many examples of recordings I made: Two Baby Barred Owls vocalizing at night.

Recorded with the brand-new AudioMoth USB Mic from Open Acoustic Devices, at an approximate distance of 15 meters.

This makes The USB Mic a good choice for those who intend on recording both ultrasonic and audible sounds.

This new microphone would also be very good for bat detecting enthusiasts/obviously, as well as those interested in recording other wildlife sounds. 

From my extensive testing, I’ve also concluded that Professionals will find it very useful as well... I find it to be robust, and pleasantly sensitive using it's default settings. You plug it into your laptop, launch the AudioMoth Live App - And it just works! Audio is coming over your laptop's speakers, loud and clear.

I believe it would be perfect for having a listen around an area, and/or before deploying the main/overnight recorders. It would be perfect for confirming the presence of animal vocalizations before deploying other overnight equipment... 

This relatively inexpensive unit, would make an excellent addition to the recording equipment of the typical recording enthusiast. With the combination of being affordable, and providing very good performance. I found the recordings to be on par with several of the detectors available today. 

I've used The AudioMoth USB Mic on: An old Samsung smartphone, running the Bat Recorder App; as well as on an iPhone running Ultrasonic Analyzer. No issues were encountered. 

I've made countless recordings of my local bats, and they were all excellent! During recording, and later on when playing back and analysing. 

These recordings will be shown/played/discussed in an upcoming presentation on The BatAbility Club (on 7/24/2023).

I hope to add some spectrograms to this review in the near future also... For now, here's a recent screenshot:

This is most likely one of my local Big Brown Bats (Eptesicus fuscus)

I'm also planning to add some related material to my YouTube channel, and SoundCloud for convenience. 

To go over the steps/to reiterate:

1. Install the AudioMoth Live App downloaded from here.
2. Plug in The USB Mic using the length of USB cable appropriate for your needs.
3. Wait for your laptop's operating system to detect and recognize The USB Microphone.
4. Launch the AudioMoth USB Live App Audio.
5. You want to choose 'File' > 'Enable high sample rate' (typically).
6. Press the green Play button (starts spectrogram scrolling).
7. Select 'Auto save file duration' (or capture wav files yourself manually).

When you first plug-in and use this AudioMoth: You will immediately recognize how accurate the microphone is at detecting and reproducing sound. There is also an option to select 'Off' which stops the spectrogram scrolling/screen.

The 'Monitor' setting, gives you the option of monitoring large swaths of incoming sound. You may also select 'Heterodyne' to provide the advantage of a heterodyne bat detector to the incoming sound. 

Pros:

• Very user-friendly, not much effort required to begin recording.
• May be used to record ultrasonic and audible sounds.
• Extremely small and lightweight.
• Described as splash proof, which means it won't deteriorate from some (accidental) light rain.
• The AudioMoth Live App works well with The Dodotronic Ultramic Evo384K Mic - It may work with the USB Mic you currently have to hand...

Cons:

• Omnidirectional only.
• Not available for purchase yet.

Getting your hands on one of these USB Mics (when they become available to the public) may be different than what you're used to. It depends...

As for where and when to order: I can't say at this time. Stay tuned! And keep checking the Open Acoustics Devices Site, as well as GroupGets and LabMaker (Earth and Ecology page).

Mid-August Update: I'm working on adding just a bit more to this review. Mostly, screen captures and an additional summary.

For now, I cannot emphasize the following statement enough:

The AudioMoth USB Microphone is a simple and robust device, which allows you to begin recording bats quickly, easily, and accurately. Especially when using the AudioMoth Live App on a laptop!

I want to be clear: This new AudioMoth USB Mic is a pleasure to use. The AudioMoth Live App designed for use with it (works with other USB Mics too) is refreshingly simple. I'm very happy with the way it represents what the Mic is hearing, as well as how easily it allows me to save the recordings.

Until next time,

Happy bat detecting!