During the calibration procedure the 371 uses AmbiSense technology to calculates the percentage of the sense signal that is picked up from the paging and/or music that is going through the sound system. AmbiSense allows music or page pickup without any ill effects on its operation, up to about a 50:50 mix of music/page to ambient. In an extreme case where the sense microphone picks up 100% music/ page (0% ambient noise), AmbiSense will not be able to extract enough information to use for gain control.Basically this is how it works:

During the first stage of calibration, the 371 measures and calculates an averaged value of both the program material, and of the signal picked up by the sense microphone. Then during the second step of calibration, after the installer manually increases the program loudness, another set of readings are taken and averaged. Now, we have four numbers:

1. Average sense signal during quiet room

2. Average sense signal during loud(er) music

3. Average program level during first calibration step

4. Average program level during second calibration step

From these numbers (and other sneaky means) we can then calculate a good estimate of what percentage of the sense signal is due to the pickup of program audio, and therefore what percentage of the sense signal is likely to reflect the actual ambient noise.