1. Hybrid Zero-Cross Analysis of Full Spectrum Recordings
David A. Riggs Tucson Echolocation Symposium

2. 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.

3. 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!

4. 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!

5. 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

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

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

8. Sample Interpolation

9. 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)

10. 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

11. 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)

12. Desktop Sensitivity Knob

13. Desktop Divratio

14. 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

15. 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

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

17. Thank You!
David A. Riggs ZCANT: Open Source ZCA in Python