Systems, methods, apparatus, and articles of manufacture are disclosed. An example playback device includes a signal detector adjacent to a first side of the playback device; a signal emitter adjacent to a second side of the playback device; a processor; and memory having stored thereon instructions executable by the processor to cause the playback device to perform functions. The example functions include detecting, by the signal detector, an analog signal; amplifying the analog signal in analog form; applying an offset to analog signal in analog form; filtering the offset signal in analog form; and emitting, by the signal emitter, the filtered signal.