Deploy SM5 Recorders for Acoustic Localization - SM5

Configure multiple SM5 recorders and microphones in a synchronized microphone array and perform the necessary measurements for time difference of arrival localization.

1. Configure appropriate settings on every SM5.
   1. On all recorders, set GPS sync to Continuous.
      Continuous synchronization is required to maintain each recorder's clock to the level of precision required for localization. Without continuous synchronization, the clocks of different recorders can drift apart from each other, creating too much error to perform localization.
   2. Set all SM5 recorders to the same Sample rate settings.
      Time synchronization between recorders is most precise when they use the same sample rate.
   3. Configure each recorder's Channel settings to use two channels, with at least one channel mapped to an external microphone port.
   4. Program the same schedule on all recorders to ensure they are all active simultaneously.
      Tip: Continuous GPS synchronization significantly increases the SM5's power consumption. To maximize battery life, limit your recording schedule to periods when you expect your species of interest will be active.
   5. Assign each recorder a meaningful Recorder name, and consider labeling the outside of each recorder with the same name.
      Your analysis will require keeping careful track of which files came from each SM5. The Recorder name will be included in the name of each audio file.
2. Position your recorders and microphones.
   Keep the following factors in mind when you position your equipment:

   • Each SM5 recorder needs a reliable GPS/GLONASS signal to maintain clock synchronicity. Very dense tree cover or nearby buildings may interfere with the recorder's satellite reception.
   • Separating the microphones with greater distances tends to produce more accurate localization, but the microphones must be close enough that at least three microphones can record any given sound of interest. With each recorder, use one external microphone with a long cable to separate that microphone from the recorder's built-in or stub microphone.
   • For most scenarios, microphones positioned across two dimensions provide better accuracy than microphones arranged in a line. For three-dimensional localization, it may be necessary to position microphones in a three-dimensional array, such as a cube arrangement.
   • Localization tends to be most accurate on sound sources inside the area bounded by the microphones, but it is still possible to localize sound sources outside the bounded area.
3. Check that each SM5 has an active GPS/GLONASS connection.
   1. Power on the SM5 at the intended deployment location and observe the status screen on the built-in display.

      The GPS: section of the status screen will indicate if the SM5 is attempting to acquire a satellite fix, how many satellites it is attempting to track, how many satellites are in view, and a measurement of average signal quality with the tracked satellites.

      For example, GPS:NoFix 3/5 25dB indicates the following information:

      NoFix

      The SM5 has not acquired a fix, and its clock is not synchronized.

      3/5

      The SM5 is tracking three satellites out of five that are in view. More satellites enable faster acquisition.

      25dB

      The average signal-to-noise ratio (SNR) among the satellites being tracked is 25 dB. Higher values indicate better signal quality and faster acquisition.

   2. After 30 seconds, if the screen does not indicate that at least 3 satellites are being tracked with approximately 20 dB SNR or higher, move the SM5 to an area with fewer obstructions nearby or overhead.
   3. Allow up to five minutes for the SM5 to acquire a fix and display GPS:Active Fix&Sync.
      The time required to acquire a fix will depend on the number of satellites being tracked and the average SNR reading. For example, with 5–7 satellites tracked and 20–25 dB SNR, it is typical to wait 2–3 minutes.
   4. Allow the SM5 to run its schedule and review the resulting recordings.
      Recordings that include a $ symbol in the file name's time stamp indicate that the SM5 maintained synchronization for the entirety of the recording duration.
   5. If any recorders failed to maintain synchronization after initially acquiring it, reposition them so they have clearer views of the sky, and repeat these tests.
4. Measure the position of each microphone's tip as precisely as possible.
   • For small survey areas with microphones positioned relatively closely, you can manually measure the position of each microphone relative to the others.
   • For larger areas, use a survey-grade GNSS receiver. Position the receiver as closely to each microphone tip as possible, or manually measure the microphone's position relative to the receiver.
5. Record voice notes identifying each microphone on each recorder.
   Audio recordings with identifying information can help you keep track of the many different audio channels from multiple recorders during your analysis.
   1. Wait until each recorder's schedule is running, or use Utilities > Instant record on the built-in screen or in the app to begin a recording outside of the programmed schedule.
   2. Tap each microphone to produce a sound in only that microphone, and speak aloud any relevant details, such as the recorder's name and location and the channel each microphone is connected to.
   3. If using , press the physical Back button or tap Stop in the app to end the recording.
6. Configure a data logger to record local temperature and humidity throughout your survey.
   Using accurate temperature and humidity data will improve the accuracy of your localization because these factors influence the speed of sound. Depending on the size of your survey area and your accuracy needs, temperature data from a nearby weather station may be sufficient.
7. Record test sounds so you can later verify your localization calculations.
   1. Place a loudspeaker in a location within or near your microphone array, close enough for at least three microphones to record the sound at a time.
   2. Precisely measure the location of the loudspeaker.
   3. While all SM5 recorders are recording, play a reference sound from the loudspeaker.
   4. If needed, reposition the speaker and repeat to test a different subset of microphones.
   When you perform your analysis, the location you derive from your localization calculations should match the actual location of the loudspeaker.