Figure 4
The dynamic squelch suppresses residual loudspeaker signals, demonstrated here for three birds connected in a hierarchical network. (a) The female T on top is bidirectionally connected (arrows) with two males L and R that are not supposed to hear each other (hierarchical network). (b–d) Example in which T and L call simultaneously (green arrows). (b) Even though Mic T records a superposition of both calls (magenta arrow), L’s call gets cleanly filtered out (MicSep T) by the LMS filter. In contrast, a louder call by L (orange arrow) leaves a significant echo on MicSep T (red arrow). The squelch removes the residual of that call on MicSepSq T (yellow arrow), which constitutes a clean signal, just as if L had been silent. Spectrograms have been normalized to individual color scales. (c,d) The squelch (magenta) is high when the mean-squared MicSep signal (d, red) falls below the dynamic threshold (d, black) composed of a fixed component and a dynamic component proportional to the mean-squared speaker signal. Shown are the Speaker T (gray), MicSep T (red), and MicSepSq T (green) sound waveforms. (d) The light magenta regions indicate times when the squelch is active and signal transmission is blocked.
