Bat Recorder is an Android app designed to record ultrasonic audio signals using an Android smartphone or tablet in conjunction with a separately purchased USB ultrasonic microphone (Please note that USB microphones require an Android device that supports USB On-The-GO).

The app can be used to record and analyze ultrasonic bat echolocation calls as well as other high frequency bioacoustic signals such as cetacean calls and insect sounds.
The app provides generic support for many 16-bit USB microphones , ultrasonic or otherwise, that support the USB audio class specifications, such as the Pettersson Elektronik M500-384 ultrasonic microphone, the Dodotronic Ultramic USB ultrasonic microphones or Hydromic USB preamplifier, Avisoft's UltraSoundGate 116Unb ultrasonic microphone, or the non-ultrasonic Samson GoMic. The app also supports Binary Acoustic Technology's miniMIC USB ultrasonic microphones. By default, the app will use the highest sampling rate supported by the microphone - however, other sampling rates can be specified in the app's Settings if the USB microphone supports doing so.

​The app can also be used to record output from many heterodyne, frequency division, or time expansion bat detectors (such as Batbox's Baton XD, which supports the latter two modes) by using an audio cable plugged into the TRRS jack. In addition, the app can be used with your Android device's built-in microphone or an external TRRS microphone to record audible sounds such as bird songs. Please note, however, that in these cases the incoming audio will not be ultrasonic. This app displays both a real-time spectrogram (linear or logarithmic scale), wave amplitude plot, and power spectrum of incoming signals and previously made recordings (saved as uncompressed, geotagged WAV files). The display can be zoomed, and the visualization can be enhanced using a variety of configurable color palettes. 
This app supports the ability to audibly monitor ultrasonic sounds simultaneously while recording using either real-time frequency division, heterodyne tuning (either manual or automatic), or using a low pass filter. In addition to these modes, recorded ultrasonic signals can  be played back in the audible range using time expansion.  Time expanded versions of recordings can also be exported (A few samples can be found here.)
The app features a resizeable overlay that displays the power spectrum for any point in a recording. In addition, in order to  facilitate call identification, the frequency and intensity at peak power at the given point in time is also displayed.

Bat Recorder can be configured to automatically trigger recordings based on frequency and intensity. Text messages or email notifications can be sent whenever a recording is automatically triggered.
The app also features a 'caliper' tool, which allows you to easily measure the frequency range and duration of a sound pulse - or the time between pulses - by simply double tapping. Fine adjustments can be made by first selecting the tool by using a long press, then using scaling and dragging gestures to resize and reposition the axes.
Bat Recorder can save GPS location and other metadata inside the WAV recordings, and supports several different metadata formats, including Myotisoft's GUANO format, Adobe's XMP format, and Wildlife Acoustic's WAMD format.

Finally, the app supports several different languages - in addition to English, the app is localized to German, Dutch, French, Italian, Spanish, Norwegian and Swedish.
Bat Recorder is available for purchase in the Google Play Store. PDF versions of the manual can be found here.
Recorded at Hampstead Heath in north London UK using a Pettersson M500-384 ultrasonic mic, a Motorola G smartphone and the Bat Recorder app.
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