ultrasonic locationing of a tag with an emitter transducer operable to emit a single frequency ultrasonic burst . a receiver with at least two microphones is operable to receive the ultrasonic burst . each microphone receiver contains two narrowband filters to extract frequencies above and below the ultrasonic burst frequency . a processor derives a low frequency waveform indicative of the phase difference between the dual frequency pulses coming from each microphone receiver . a correlator then determines the time difference of arrival between each microphone receiver by correlating the phase difference waveforms . this invention enables the creation of an ultrasonic locationing system requiring microsecond accuracy on tdoa data , as is necessary with microphone spacing of less than one foot , while using a simple single high frequency emitter source .