This app has been developed as a volunteer effort to help increase the monitoring and reporting of bats and also to show that it could be done.
Please note for the full functionality of the app you have to have an external USB microphone and an android device capable of acting as a USB host.
The app takes input from three possible sources, an external USB microphone, the device microphone or a saved file.
When an external USB mic is attached and the app is started, the spectrogram should show the spectrogram from the USB microphone. You have to set the frequency that the mircophone records at. This is important as otherwise all the calculations are wrong. Look in "setting->Sample rate" for the choice of frequencys. By changing the "Samples per window" you can change the speed of the display.
It is possible to save the sound recorded either all the time by pressing the "Continuous Save" button and wav files of the length "setting->Continuous Save File Length(Sec)" are stored into the location "UsbBatDetector/". If the "Save" button is pressed then a file of length "setting->Segment Save Length(sec)" is stored in the same directory. This is the sound from the last few few seconds, so should save what is seen on the screen.
A sound is also played back and this sound is similar to that of a hydrodyne bat detector. You can change the frequency this sound is tuned to with the +/- buttons. By pressing "scan" frequencies from 20kHz to 60kHz are automatically sequentially selected. This sound playback is meant to give a audio indication that there is something worth looking at. I would like to improve the quality of this sound but that is future work.
By pressing the "File Select" you can playback a saved file in near real time.
If no USB mic is attached then the device mic is used. Only the spectrogram is shown but no saving or sound playback is possible.
If you touch the running spectrogram the display stops and then you have to press the arrow button to make it go again. Sounds in this stopped time will be missed.
The blue lines across the screen when spectrogram is running are at 25kHz 45kHz 55kHz and 80kHz. This gives some perspective on what frequency the sound is at. This is unashamely biased to the most common bats in Ireland where the app was developed and tested.
Please note that it is always best to restart the app after changing any of the "setting"
Also turn of Wifi and Bluetooth on your device will using as they both cause interference.
There are a HUGE number of android devices and not all of them support USB devices so I was not able to test this app on even a tiny percentage of the total. Testing was mostly done on a Nexus 7 but I have verified that app does work on at least some Samsung/LG/Sony phones/tablets. I know it doesn't work on a Samsung tab 4 or a Sony Xperia L.
This app is pretty heavy on the battery. I have run it for ~60mins on a fully charged Nexus 7. I'd would expect it to drain a phone battery fairly quickly.
The USB Mic device that was primarily used for the testing of this app was a Petterson "M500-384 USB Ultrasound Microphone". Thanks to Lars Petterson for his help and encouragement and access to a nice bit of kit, see http://www.batsound.com/. I have also tested with a 250 kHz microphone from Dodotronic
This app was developed as a not for profit effort as a personal challenge and also to increase the reporting of bat species. While I developed the app on my own I used software that I in good faith think was free to use. I have maybe not chased all the software included in software I have used but I think its all free to use. Thanks to all I hope my app puts your efforts to good use.