Which of our song meters is right for your research?
Below the comparison table you can find more information about evaluating wildlife recorders for your needs.
The Signal to Noise Ratio (SNR) relates to the relative electronic background noise caused by limitations of the microphone sensor and electronics. A higher SNR implies that the recorder will be able to detect quieter signals at a greater distance before the signal is lost in the noise. A recorder with 6dB greater SNR can detect signals twice as far away unless the environmental background noise (e.g. from wind, rain, road noise, airplanes, or other competing signals) is greater than the electronic background noise.
SNR is frequency dependent in that a recorder may have higher or lower relative SNR at different frequencies. The SNR Chart below can be used to assess the signal-to-noise ratio for frequencies of interest e.g. of specific bird or frog species.
In the Song Meter family, the SM4 has the best SNR at 80dB, followed closely by the Mini at 78dB, and then the Micro at 70dB (A-weighted at 1kHz re 1Pa). This is equivalent to a relative range of approximately 100%, 79%, and 32% respectively in an otherwise quiet environment.
The Frequency Response of a recorder relates to the fidelity of recording a signal across a range of frequencies. A flatter frequency response results in a more accurate representation of the signal, while a less flat frequency response might over or under represent the energy at different frequencies. The Frequency Response Chart below can be used to assess the frequency response. Note that frequency response can also be affected by the angle of incidence of sounds and interference from the tree or other structures to which the recorder is mounted.
In the Song Meter family, the SM4 has the flattest frequency response with a standard deviation of only 6dB from 100-20,000Hz. The Mini has a standard deviation of 7dB, and the Micro has a standard deviation of 10dB.
A High-Pass Filter (HPF) can reduce the energy of low frequency signals. Because most environmental noise caused by wind, rain, road noise, airplanes, etc., are concentrated in lower frequencies, a high-pass filter can prevent clipping. Clipping occurs when the digital samples reach their maximum possible value resulting in distortion.
In the Song Meter family, the SM4 offers the greatest flexibility of high-pass filters which can be set independently on the two channels to optimize for different conditions and species of interest. The Mini and Micro have a fixed 100Hz high-pass filter.
Anti-Alias Filter: Aliasing is when energy at frequencies above one half of the sample rate are folded into the recording. An anti-alias filter can improve SNR by removing unwanted high-frequency signals. This is especially true in environments with broadband noise such as that caused by wind and rain. An anti-alias filter is really a low-pass filter typically related to the sample rate.
In the Song Meter family, the SM4 offers the strongest anti-alias filter reaching 55dB of signal reduction at 60% of the sample rate. The Mini has a much weaker anti-alias filter reaching only 12dB of signal reduction at 60% of the sample rate plus a 2-pole low-pass filter at 20kHz. And the Micro has the weakest anti-alias filter reaching only 6dB of signal reduction at 60% of the sample rate plus a 2-pole low-pass filter at 10kHz.
Adjustable Gain: Gain relates to the level of amplification of a signal. Too much gain can cause loud signals to clip resulting in distortion. Too little gain may not provide enough resolution (digital bits) in weaker signals resulting in a loss of fidelity. Adjustable gain allows flexibility to choose the optimum gain setting for a given deployment.
The SM4 offers the greatest flexibility with a switchable low-noise 26dB gain pre-amplifier and additional gain of 0-59.5dB in 0.5dB increments. The Mini and Micro offer 4 gain settings in 6dB increments between 6 and 24dB.
Test conditions: 48kHz sample rate, default gain and filter settings, calibrated sound source 1m from front of recorder (perpendicular to microphone)
Test conditions: 48kHz sample rate, default gain and filter settings, calibrated sound source 1m from front of recorder (perpendicular to microphone)
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Wildlife Acoustics, Inc.
3 Mill and Main Place, Suite 210
Maynard, MA 01754-2657 USA
+1 (978) 369-5225
+1 (888) 733-0200