Methods, systems, and apparatus to calculate distance from audio sources

1. A method to calculate a distance between a portable audio collecting device and a reference audio collecting device, comprising:

receiving, at the reference audio collecting device, a first radio frequency (RF) signal from the portable audio collecting device to cause the reference audio collecting device to begin storing a plurality of reference data samples, each of the reference data samples associated with an indication of a respective time of acquisition;

receiving, at the reference audio collecting device, a second RF signal containing a plurality of embedded portable data samples of ambient audio collected at the portable audio collecting device, the embedded portable data samples being offset from the reference data samples by a dwell period, the dwell period to prevent collection and storage of portable data samples at the portable audio collecting device that are lacking an overlap parity with the reference data samples collected at the reference audio collecting device, wherein each of the portable data samples is associated with an indication of a respective time of acquisition;

selecting a set of the portable data samples having a highest relative correlation value to a set of reference data samples;

subtracting the indication of times of respective pairs of the selected sets of samples to form a difference value; and

calculating a distance between the portable audio device and the reference audio collecting device based on the difference value.

2. A method as described in claim 1 , wherein each indication of the respective time of acquisition corresponds to an integer number of collected data samples.

3. A method as described in claim 2 , wherein each integer number of collected data samples is separated by a known duration.

4. A method as described in claim 2 , wherein the data samples are collected at a constant data acquisition frequency.

5. A method as described in claim 1 , further comprising searching for a threshold increase among the correlation values calculated for sets of the portable data samples and the reference data samples.

6. A method as described in claim 5 , wherein the threshold increase among the correlation values is indicative of overlap between the reference data samples and the portable data samples.

7. A method as described in claim 1 , wherein the indication of the respective time of acquisition associated with each of the plurality of data samples is based on a number of data samples from the first RF signal.

8. A method as described in claim 7 , wherein the indication of the respective time of acquisition associated with the portable data samples is based on an integer value having a constant delay value.

9. A method as described in claim 8 , wherein the constant delay value is measured from the first RF signal.

10. A method as described in claim 1 , wherein the highest relative correlation value identifies a match between ambient audio stored by the reference audio collecting device and the portable audio collecting device.

11. An apparatus to calculate a distance between a portable audio collecting device and a reference audio collecting device, comprising:

a radio frequency (RF) interface to receive an initialization signal from the portable audio collecting device to cause the reference audio collecting device to begin storing a plurality of data samples;

a processor to associate each of the reference data samples with an indication of a respective time of acquisition; and

a correlation engine configured to:

identify a highest relative correlation value associated with portable data samples

associated with ambient audio and a set of the reference data samples, the portable data samples offset from the set of reference data samples by a dwell period configured to prevent collection and storage of portable data samples that are lacking an overlap parity with the set of reference data samples collected at the reference audio collecting device,

calculate a difference value between an indication of a time of acquisition of the portable data samples and the set of the reference data samples, and

calculate a distance value based on the difference value.

12. An apparatus as described in claim 11 , wherein the processor associates an integer number of collected data samples with the indication of a respective time of acquisition.

13. An apparatus as described in claim 11 , wherein the correlation engine searches for a threshold increase of a correlation value to identify the highest relative correlation value.

14. An apparatus as described in claim 13 , wherein the correlation engine is to identify an indication of overlap between the reference data samples and the portable data samples in response to the threshold increase of the correlation value.

15. A method to collect ambient audio in a monitored area, comprising:

transmitting a radio frequency (RF) initialization signal from a portable audio collecting device to cause a reference audio collecting device to begin storing reference data samples associated with ambient audio in the monitored area;

initiating a dwell period on the portable audio collecting device in response to transmitting the RF initialization signal configured to reduce a number of ambient audio data samples collected by the portable audio collecting device that are lacking an overlap parity with the reference data samples stored by the reference audio collecting device;

collecting ambient audio in the monitored area as portable data samples for a portable collection duration in response to an expiration of the dwell period; and

transmitting, to the reference audio collecting device, the portable data samples after the portable collection duration via an RF signal, facilitating correlation calculations between the reference data samples and the portable data samples.

16. A method as described in claim 15 , wherein a duration of the dwell period is set based on a size of the monitored area.

17. A method as described in claim 16 , further comprising dividing a length or width of the monitored area by the speed of sound to calculate the duration of the dwell period.

18. A method as described in claim 15 , further comprising decimating the portable data samples before transmitting the portable data samples to the reference audio collecting device.

19. A method as described in claim 18 , wherein decimating the portable data samples comprises applying a scale factor to the portable data samples.

20. A machine accessible storage device or storage disk having instructions stored thereon that, when executed, cause a machine to, at least:

receive, at a reference audio collecting device, a first radio frequency (RF) signal from a portable audio collecting device to cause the reference audio collecting device to begin storing a plurality of reference data samples, each of the reference data samples associated with an indication of a respective time of acquisition;

receive a second RF signal containing a plurality of embedded portable data samples of ambient audio collected at the portable audio collecting device, the embedded portable data samples being offset from the reference data samples by a dwell period, the dwell period configured to prevent collection and storage of portable data samples at the portable audio collecting device that are lacking an overlap parity with the reference data samples collected at the reference audio collecting device, wherein each of the portable data samples associated with an indication of a respective time of acquisition;

select a set of the portable data samples having a highest relative correlation value to a set of reference data samples;

subtract the indication of times of respective pairs of the selected sets of samples to form a difference value; and

calculate a distance between the portable audio device and the reference audio collecting device based on the difference value.

21. A machine accessible storage device or storage disk as described in claim 20 having instructions stored thereon that, when executed, cause a machine to assign each indication of the respective time of acquisition as an integer number of collected data samples.

22. A machine accessible storage device or storage disk as described in claim 20 having instructions stored thereon that, when executed, cause a machine to search for a transition between a negative correlation value and a positive correlation value to identify the highest relative correlation value.

23. A machine accessible storage device or storage disk as described in claim 20 having instructions stored thereon that, when executed, cause a machine to search for a threshold increase among the correlation values calculated for sets of the portable data samples and the reference data samples.

24. A machine accessible storage device or storage disk as described in claim 20 having instructions stored thereon that, when executed, cause a machine to identify the highest relative correlation value as a match between ambient audio stored by the reference audio collecting device and the portable audio collecting device.

25. A machine accessible storage device or storage disk as described in claim 20 having instructions stored thereon that, when executed, cause a machine to compute the correlation value via at least one of a normalized correlation, a Pearson correlation or a rank correlation.