Methods and apparatus to detect spillover in an audience monitoring system

1. An apparatus to distinguish local media from spillover media, the apparatus comprising:

means for sampling first and second audio signals, the first audio signal received from a source by a first microphone, the second audio signal associated with the source and received by a second microphone, the second microphone being separated from the first microphone by a first distance;

first means for calculating a time delay between receipt of the first and second audio signals;

first means for determining whether the time delay is within a threshold time difference; and

means for retaining media associated with the source when the time delay is within the threshold time difference, the means for retaining to ignore the media associated with the source when the time delay exceeds the threshold time difference.

2. The apparatus as defined in claim 1 , further including:

second means for calculating first and second absolute value audio signals, the first audio signal corresponding to an absolute value of the first audio signal, the second absolute value audio signal corresponding to an absolute value of the second audio signal; and

means for applying first and second thresholds to the first and second audio signals, respectively.

3. The apparatus as defined in claim 2 , further including means for removing (1) ones of samples from the first audio signal with intensities below the first threshold and (2) ones of samples from the second audio signal with intensities below the second threshold.

4. The apparatus as defined in claim 3 , wherein the first and second thresholds are determined to cause a removal of a majority of the samples from the first and second audio signals.

5. The apparatus as defined in claim 1 , further including third means of calculating (1) a first moving average of the first audio signal and (2) a second moving average of second audio signal.

6. The apparatus as defined in claim 5 , further including:

first means for selecting first samples from the first audio signal;

second means for selecting second samples from the second audio signal; and

second means for determining a first correlation value between the first samples and the second samples.

7. The apparatus as defined in claim 6 , wherein:

the second means for selecting to further select third samples from the second audio signal, the third samples being offset from the second samples by a first number of samples; and

the second means for determining to further determine a second correlation value between the first samples and the third samples, the time delay being determined using a greater one of the first correlation value and the second correlation value.

8. An apparatus to distinguish local media from spillover media content comprising:

means for sampling first and second audio signals, the first audio signal received from a source by a first microphone, the second audio signal associated with the source and received by a second microphone, the second microphone being separated from the first microphone by a first distance;

first means for calculating an origin direction of the source based on a time difference between receipt of the first and second audio signals;

first means for determining whether the origin direction is within a threshold angle; and

means for retaining media associated with the source when the origin direction is within the threshold angle, the means for retaining to ignore the media associated with the source when the origin direction exceeds the threshold angle.

9. The apparatus as defined in claim 8 , further including:

second means for calculating first and second absolute value audio signals, the first absolute value audio signal corresponding to an absolute value of the first audio signal, the second absolute value audio signal corresponding to an absolute value of the second audio signal; and

means for applying a first and second threshold to the first and second audio signals, respectively.

10. The apparatus as defined in claim 9 , further including means for removing (1) ones of samples from the first audio signal with intensities below the first threshold and (2) ones of samples from the second audio signal with intensities below the second threshold.

11. The apparatus as defined in claim 10 , wherein the first and second thresholds are determined to cause removal of a majority of the samples from the first and second audio signals.

12. The apparatus as defined in claim 8 , further including:

first means for selecting first samples from the first audio signal;

second means for selecting second samples from the second audio signal; and

second means for determining a first correlation value between the first samples and the second samples.

13. The apparatus as defined in claim 8 , wherein the source is a media device.

14. The apparatus as defined in claim 8 , wherein the threshold angle is based on a physical location of the source.

15. An apparatus to distinguish local media from spillover media, the apparatus comprising:

means for sampling first and second audio signals, the first audio signal associated with media received by a first microphone, the second audio signal associated with the media received by a second microphone, the second microphone being separated from the first microphone by a first distance;

first means for calculating a time delay between receipt of the first and second audio signals;

first means for determining whether the time delay is within a threshold time difference; and

means for identifying the media as local media when the time delay is within the threshold time difference, the means for identifying to identify the media as spillover media when the time delay exceeds the threshold time difference.

16. The apparatus as defined in claim 15 , further including:

second means for calculating a first and a second absolute values of the first audio signal and the second audio signal, respectively; and

means for applying first and second thresholds to the first and second audio signals, respectively.

17. The apparatus as defined in claim 16 , further including means for removing (1) ones of samples from the first audio signal with intensities below the first threshold and (2) ones of samples from the second audio signal with intensities below the second threshold, the first and second thresholds are determined such that removing samples from the first and second audio signals removes a majority of the samples from the first and second audio signals.

18. The apparatus as defined in claim 15 , further including:

third means for calculating a first and second moving averages of the first and second audio signals, respectively;

first means for selecting first samples from the first audio signal;

second means for selecting second samples from the second audio signal; and

second means for determining a first correlation value between the first samples and the second samples.

19. The apparatus as defined in claim 18 , wherein (1) the first samples are equally spaced between a first point in time and a second point in time in the first audio signal and (2) the second samples are equally spaced between the first point in time and the second point in time in the second audio signal.

20. The apparatus as defined in claim 18 , wherein:

the second means for selecting is to further select third samples from the second audio signal, the third samples being offset from the second samples by a first number of samples; and

the second means for determining to further determine a second correlation value between the first samples and the third samples, the time delay being determined using a greater one of the first correlation value and the second correlation value.