Ultra High definition spectrograms

The bitmap spectrograms in the bat sonar gallery have frequency resolutions limited by the 240 pixel count of the analyser LCD. The calculations are actually carried out to much higher precision, as shown in the spectrograms below, which are extracts of sonar from CF (constant frequency) bats.

Here, the frequency scales are shown magnified by fifty times to 200 Hz / pixel, except for Dusky leaf-nosed which is 100 Hz / pixel.
DFT sample lengths are only 64, except for Greater horseshoe[2], which is increased to 256.

These "phase integrated" DFT spectrograms, although a huge improvement over conventional DFT plots, are still inferior to theoretical limits, due to quantisation effects (with only 16-bit arithmetic) and signal noise - electronics, echoes, background.

 

 

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