SM2BAT and SonoBat What’s going on?

Background There has been some feedback that SM2BAT and SonoBat do not integrate well together. SonoBat software discards calls recorded with SM2BAT because of “call quality,” a metric of several factors internal to SonoBat. We finally have side-by-side data from Joe to analyze with his input and support. (Thanks, Joe!) What does Wildlife Acoustics think is going on?

Areas of Investigation Discussed in following slides: (1) Signal to Noise Ratio: WAC Compression (2) Microphone frequency response: WAC2WAV compensation (3) Sonabat truncation

Signal to Noise Ratios Early comparisons suggested that weak signals may be getting lost in the noise. Sure enough! Analysis of signals revealed our recommended WAC4 compression lost some subtleties in the recorded signals. We now recommend WAC0 (lossless) compression to retain all details in the signals.

WAC4 at +48dB adds noise >60kHz

Frequency Response Joe suggested we explore differences in the microphone frequency responses. Our SMX-US microphone is 20dB more sensitive below 55kHz compared to above 65kHz. Further analysis has revealed that previous WAC2WAV compensation provided incomplete compensation. New WAC2WAV depresses sensitive region to better flatten response with a simple digital filter.

How flat is flat? In practice, no microphone can achieve an ideal perfectly “flat” frequency response. According to data provided by Lars, the D500X response (which is flattened from a stock FG microphone element response) is still +/- 5dB of “flat” from kHz. With new Wac2Wav compensation, the SM2BAT is equally “flat.” But differently so…

SM2BAT new comp vs D500X

Modeling D500X vs SM2BAT Signal to noise ratio With WAC0, our analysis of data from Knowles (mfgr of both FG and MEMS elements) and from Lars, the SNR of the two systems appears comparable within 5dB. At some frequencies, one system may have advantages over the other. Frequency response With new Wac2Wav compensation, both systems are equally flat to within +/-5dB. But they are different. So we now expect similar results…

Side-by-side testing – Still not right! Even with WAC0 and new v3.2.1 compensation, SonoBat still interprets SM2BAT recordings as having poor call quality. But… A closer look of the recordings with Song Scope (and just for kicks, we also used Cornell’s Raven with similar results) – the side-by-side calls reveal comparable bandwidth. We can clearly see frequency content that SonoBat rejects.

Call #1 – Song Scope vs Sonobat

Call #2 – Song Scope vs Sonobat

Call #3 – Song Scope vs Sonobat

Spectrum analysis of 3 bat calls from SM2BAT and D500X – pretty close!

Difference between SM2BAT and D500X – just 5dB in two areas

This bat’s 3 calls were more variable than the two recorders.

Better results achievable with tweaks to Sonobat. WAC0 and new v3.2.1 compensation achieves comparable frequency response and signal content... …and Joe can tweak SonoBat to recognize the full signal content.

Call #1 – Song Scope vs SonoBat Same call #1 with WAC2WAV v3.2.1 compensation and enhanced SonoBat sensitivity.

Call #2 – Song Scope vs SonoBat Same call #2 with WAC2WAV v3.2.1 compensation and enhanced SonoBat sensitivity.

Call #3 – Song Scope vs SonoBat Same call #3 with WAC2WAV v3.2.1 compensation and enhanced SonoBat sensitivity.

Conclusions of Analysis WAC0 and Wac2Wav compensations result in SM2BAT recordings which are comparable to D500X recordings within 5dB across the frequency spectrum. Manufacturer specs on both FG and MEMS have a +/- 5dB tolerance. Similar differences could exist between two of the same models and is considered insignificant. SonoBat to be enhanced to respond with less sensitivity to these minor differences and avoid truncation

Call to Action Use WAC0 not WAC4. SonoBat users should use the new Wac2Wav utility and turn on the new SMX-US compensation filter. SonoBat users should obtain the new utility from Joe for optimizing the resulting WAV files produced by WAC2WAV for use with SonoBat.