Methods, systems, and apparatus to synchronize actions of audio source monitors

1. A method to calibrate a delay period between an audience monitor and a base unit, comprising:

invoking an audience monitor to transmit a radio frequency (RF) initialization packet to a base unit;

receiving an indication that the base unit has received the RF initialization packet at a first time;

invoking the base unit to transmit an RF acknowledgement packet to the audience monitor;

after receiving an indication that the RF acknowledgement packet is received by the audience monitor, identifying whether the audience monitor has finished processing the RF acknowledgement packet when a delay period having a first value based on a room size ends at a second time; and

incrementing the delay period to a second value when the audience monitor is still processing the RF acknowledgement packet and the delay period has ended, the second value based on an increase of the difference between the first time and the second time.

2. A method as described in claim 1 , further comprising calculating a percentage increase of the difference between the first time and the second time as the second value.

3. A method as described in claim 1 , further comprising altering a packet length of the RF acknowledgement packet to determine whether to increase the delay period to a third value.

4. A method as described in claim 1 , further comprising calculating the first value based on a likelihood that a first audio sample occurring after the delay period will be received by the base unit.

5. A method as described in claim 1 , wherein the first value corresponds to a maximum distance the audience monitor is from the base unit.

6. A system to determine a delay period of an audience monitor, comprising:

a calibration test manager to invoke an audience monitor to transmit a radio frequency (RF) initialization packet to a base unit;

a base unit interface to receive an indication that the base unit has received the RF initialization packet at a first time, the calibration test manager to invoke the base unit to transmit an RF acknowledgement packet to the audience monitor;

an audience monitor interface to receive an indication that the audience monitor has received the RF acknowledgement packet, the calibration test manager to identify whether the audience monitor has finished processing the RF acknowledgement packet when a delay period having a first value based on a room size ends at a second time; and

a delay period adjuster to increment the delay period to a second value when the audience monitor is still processing the RF acknowledgement packet when the delay period having the first value ends, the second value based on an increase of the difference between the first time and the second time.

7. A system as described in claim 6 , further comprising a trigger monitor to monitor the audience monitor to determine whether the audience monitor is still processing the RF acknowledgement packet.

8. A system as described in claim 7 , wherein the trigger monitor monitors a processor pin of the audience monitor to determine an activity state of the processor.

9. A method to initiate a recording action of a first audience recording unit, comprising:

transmitting, from the first audience recording unit, a radio frequency (RF) initialization packet to a base unit at a first time and monitoring for a corresponding RF acknowledgement packet;

waiting for a delay period in response to receiving the RF acknowledgement packet from the base unit, the delay period of the first audience recording unit based on a room size and equal to a delay period of the base unit, and initiated by the RF acknowledgement packet;

initiating an audio recording action on the first audience recording unit when the delay period of the first audience recording unit expires; and

incrementing the delay period of the first audience recording unit to a second value when the audience recording unit is still processing the RF acknowledgement packet at a second time, the second value based on an increase of the difference between the first time and the second time.

10. A method as described in claim 9 , further comprising maintaining the audio recording action on the first audience recording unit for a first duration that is dissimilar to a second duration associated with a second audience recording unit.

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

invoke an audience monitor to transmit a radio frequency (RF) initialization packet to a base unit;

receive an indication that the base unit has received the RF initialization packet at a first time;

invoke the base unit to transmit an RF acknowledgement packet to the audience monitor;

identify, after receiving an indication that the RF acknowledgement packet is received by the audience monitor, whether the audience monitor has finished processing the RF acknowledgement packet when a delay period having a first value based on a room size ends at a second time; and

increment the delay period to a second value when the audience monitor is still processing the RF acknowledgement packet and the delay period has ended, the second value based on an increase of the difference between the first time and the second time.

12. A machine accessible storage device or storage disk as described in claim 11 having instructions stored thereon that, when executed, cause a machine to calculate a percentage increase of the difference between the first time and the second time as the second value.

13. A machine accessible storage device or storage disk as described in claim 11 having instructions stored thereon that, when executed, cause a machine to alter a packet length of the RF acknowledgement packet to determine whether to increase the delay period to a third value.

14. A machine accessible storage device or storage disk as described in claim 11 having instructions stored thereon that, when executed, cause a machine to calculate the first value based on a likelihood that a first audio sample occurring after the delay period will be received by the base unit.

15. A machine accessible storage device or storage disk as described in claim 11 having instructions stored thereon that, when executed, cause a machine to set the first value to correspond to a maximum distance the audience monitor is from the base unit.

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

transmit, from the first audience recording unit, a radio frequency (RF) initialization packet to a base unit at a first time and monitoring for a corresponding RF acknowledgement packet;

wait for a delay period in response to receiving the RF acknowledgement packet from the base unit, the delay period of the first audience recording unit based on a room size and equal to a delay period of the base unit, and initiated by the RF acknowledgement packet;

initiate an audio recording action on the first audience recording unit when the delay period of the first audience recording unit expires; and

increment the delay period of the first audience recording unit to a second value when the audience recording unit is still processing the RF acknowledgement packet at a second time, the second value based on an increase of the difference between the first time and the second time.

17. A machine accessible storage device or storage disk as described in claim 16 having instructions stored thereon that, when executed, cause a machine to maintain the audio recording action on the first audience recording unit for a first duration that is dissimilar to a second duration associated with a second audience recording unit.