Hybrid Zero-Cross Analysis of Full Spectrum Recordings David A. Riggs driggs@myotisoft.com 2017-03-30 Tucson Echolocation Symposium

Presentation Goals Share lessons learned from a journey converting FS to ZC Show benefits of hybridizing FS techniques to ZCAnalysis Help re-think the possibilities of ZCA Share a new FS-ZCA tool …and try not to rehash what’s already been said.

FS and ZC Recording vs Analysis Distinction between recording in ZC versus ZCAnalysis There are cases where ZC recording may be optimal: Longterm passive Remote access Power/memory/storage constrained devices If you can “afford” it, record in FS if doing ZCA!

My Own Journey “Converting FS to ZC is trivial.” 2012 – 2013 FWS Indiana Bat Guidance recommended EchoClass (Britzke) for auto-ID in US Northeast We were recording in full-spectrum, EchoClass is based on Anabat filters Quickly produced ZCANT for batch FS-to-ZC conversion Excellent results… given excellent recordings. Terrible results with average recordings! “Conversion” is trivial, doing it well isn’t Also… learning to manually vet calls involves lots of qualitative analysis!

Samplerates The width of a digital sample increases with lower samplerates A frequency-divided signal’s FD wavelength gets smaller with decreasing divratio The frequency resolution of a ZC is impacted by lower samplerates and/or by lower divratio

Sample Interpolation… 10 sec 100kHz sin sweep, Divratio 8, no sample interpolation

Sample Interpolation… 10 sec 100kHz sin sweep, Divratio 8, with linear sample interpolation

Sample Interpolation

Etc. Noise gate required for clean calls (equivalent to Anabat sensitivity) Low frequencies overpower higher frequencies, HPF may be required (an Anabat has ~8kHz HPF)

Amplitude – The 3rd Dimension ZCANT incorporates time, frequency, and amplitude for ZCA Mean absolute sample value for each “dot” (FD cycle) Whether amplitude is relevant to ID or not, it can indicate QUALITY Amplitude used to: Scale dot size Weight freq histogram

ZCANT: Open Source ZCA Tool Dots scaled by amplitude Color by slope Histogram weighted by amplitude HPF, noise gate, compressed/realtime, log/linear Open Source – MIT License (PROJECT not product)

Desktop Sensitivity Knob

Desktop Divratio

Anabat Format Updates Anabat file format was limited to 32kb size, 15 sec length, 16,384 dots Those limits relaxed by Chris Corben, Analook supports “big” files now GUANO metadata allows experiments like ZCA with amplitude

Others’ Approaches KaleidoscopePro uses very sophisticated DSP capable of tracing signals even where a traditional ZC algorithm can’t SonoBatLIVE displaying realtime ZC of the n strongest frequencies

Conclusions(?) Record in full spectrum whenever you can Don’t blindly trust any FS-to-ZC program Reconsider what can be done with ZCA!

Thank You! David A. Riggs driggs@myotisoft.com ZCANT: Open Source ZCA in Python http://myotisoft.com/products/zcant https://github.com/riggsd/zcant