Based on the powerful SM2 Platform, the Song Meter SM2 Terrestrial Ultrasonic Package (SM2-TUP) includes one removable weatherproof omni-directional and highly sensitive broadband ultrasonic microphone and the factory-installed SM2BAT recorder daughter-card, either in 192kHz stereo or 384kHz mono.

Unlike other bat detectors and recorders, the SM2BAT can record 16-bit resolution audio samples at 192kHz on one or two channels continuously without any gaps of coverage while preserving amplitude and harmonic details of the signal.

Using a powerful digital signal processor, SM2-TUP adapts to changing background noise conditions to automatically detect, compress and record bat activity resulting in typical compression ratios of 30:1 during periods of bat activity and 100:1 to 200:1 without. This means that SM2BAT has the storage capacity to monitor continuously for thousands of hours at a time.

SM2-TUP consumes less power than any other full spectrum bat detector on the market today for longer field deployments from the same battery weight. With just 4 D alkaline batteries, SM2-TUP can record for 100 hours, or about 8-10 nights. External power can be used to extend recording time.

SM2-TUP is not only the least expensive remote bat detector/recorder on the market, but it is also packed with capabilities to reduce deployment costs. The recorder and microphones are weatherproof, so no extra weatherproofing is required. The low-impedance microphones can drive cables longer than 100 metresso no external preamplifier is required. And with two channels and omni-directional microphones, it's like having two recorders in one. The other channel can also be fitted with a standard acoustic microphone for monitoring birds and frogs simultaneously or at different times. SM2-TUP even has a built-in temperature sensor and data logger.

The SM2 Ultrasonic Stereo 192kHz option includes a two-channel 192kHz 16-bit sample rate card and one SMX-US weatherproof ultrasonic microphone. With two channels, it's like having two bat detectors in one. A second ultrasonic microphone extended on a cable can be used to monitor bats up to 100 metres away. For example, one microphone could be mounted at nacelle height and another near ground level to meet the requirements of many wind farm pre-construction surveys. Alternatively, the second channel could also be used with a conventional acoustic microphone to record birds, frogs, and other wildlife either simultaneously or at different scheduled times with bat monitoring. Bat echolocation calls up to 96kHz can be recorded, sufficient for monitoring nearly all species present in North America.

The SM2 Ultrasonic Mono 384kHz option includes a one-channel 384kHz 16-bit sample rate card and one SMX-US weather resistant ultrasonic microphone for recording bats at higher frequencies. The second channel can still be used with a conventional SMX-II acoustic microphone to record birds, frogs, and other wildlife at different scheduled times, but not simultaneously with ultrasonic monitoring. Bat echolocation calls up to 192kHz can be recorded, sufficient for monitoring most species present in Europe.

With four high-capacity flash card slots, SM2-TUP can store up to 128GB of data at a time, or about 92 continuous uncompressed hours of one-channel 192kHz 16-bit audio. Our lossless and lossy compression algorithms can increase this up to 5-fold for over 450 hours of continuous non-stop recording. Finally, our adaptive triggering automatically adjusts to changing ambient background noise levels and can be configured to begin recording when bat activity is first detected, and continue recording until no bat activity is detected for a specified period of time. This technique typically achieves 30:1 compression during periods of bat activity and 100:1 to 200:1 without. In a typical night with some bat activity, compression ratios of better than 50:1 can be achieved. This translates to between 4,000 and 5,000 hours of monitoring using 4x32GB flash cards.

The SM2-TUP uses almost no power when idle between scheduled recording periods and can record up to 100 hours on just 4 D-size alkaline batteries spread out through several weeks or months at a time. An optional power adapter can be used to connect SM2-TUP to larger external batteries or a solar power source for longer deployments.

The SMX-US ultrasonic microphone is weatherproof and omnidirectional to maximise detection of bats from all directions. Most other ultrasonic recorders use a narrow-beam electrostatic transducer. These electrostatic transducers have a beam angle that is only 15 degrees wide (at -6dB attenuation) and are therefore only sensitive to bats flying almost directly in front of the transducer (or reflector plate). By contrast, the SMX-US has an equivalent beam angle of more than 100 degrees (at -6dB attenuation) and has a loss of less than 15dB in almost all directions. This means the SM2-TUP can detect more bats.

SM2-TUP is a continuous full-spectrum ultrasonic recorder. This has many advantages over some other bat detector technologies like time compression, heterodyne, and zero crossing.

Time compression recorders operate by buffering up ultrasonic samples at high speed until a memory buffer fills, then dumping the buffer out at audio rates to a conventional audio recording device. While this is full spectrum recording, it is not continuous. For example, if ultrasonic samples fill the buffer at 192kHz and then empty to the audio recorder at 44.1kHz, the recorder is only recording about 23% of the time. That means you are missing 77% of your bat calls!

Heterodyne recorders operate by shifting a narrow band of frequencies into the audio spectrum and recording to a conventional audio recorder. These recorders are continuous, but they can only look at a narrow frequency range at any given time. For example, a heterodyne recorder could record frequencies between 20-64kHz or between 50-94kHz, but not both simultaneously. That means you can't simultaneously monitor both species with high-frequency and low-frequency echolocation calls.

Zero-crossing recorders operate by measuring the time between transitions from positive to negative pressure levels in the audio signal. The resulting data is highly compact compared to storing uncompressed digitized samples at high sample rates, and zero crossing analysis can be used to estimate the frequency track of echolocation calls. However, this method achieves high compression ratios at the expense of spectral detail as there is no amplitude information and only one frequency represented at each point in time. The thresholds used by zero-crossing detectors also limit sensitivity. That means you can't detect or identify weak or distant calls. By contrast, the SM2-TUP is capable of similar compression ratios using audio compression and adaptive triggering techniques, but also preserves all the amplitude and frequency information present in the original signal.

While the SM2-TUP is capable of collecting significantly more information than legacy time compression or zero-crossing approaches, the free Wac2Wav software can now manipulate SM2 recordings in post-processing to make it possible to use zero crossing analysis software such as Analook, and to simulate the trigger protocols of these legacy methods.

Wac2Wav Post-Processing of SM2 Recordings

• Batch processing of ".wac" audio files collected from SM2-TUP
• Optionally limit each trigger to a specified maximum duration and optionally events until a minimum space between triggers is reached. This can simulate the work flow of time expansion detectors
• Optionally "scrub" files and drop any files that do not appear to contain echolocation calls
• Optionally write output to format compatible with legacy zero crossing analysis software
• You still have the original full-spectrum recordings with all the temporal and frequency detail for additional analysis by Song Scope

SonoBat software provides a comprehensive tool for analysing and comparing high-resolution full-spectrum sonograms of bat echolocation calls. The Wac2Wav software can convert SM2 triggered recordings into individual recording files for analysis by SonoBat or BatSound. You can use the SonoBat "scrubber" or have Wac2Wav "scrub" files for you, automatically eliminating recordings that do not appear to contain bat echolocation calls.

New features in Song Scope bioacoustics analysis software let it handle ultrasonic recordings.