The Acceptable Noise Level (ANL) is a measurement of the background noise level (BNL) to the most comfortable level (MCL) ratio.

This measurement was established by Dr. Mark Ross from the Rehabilitation Engineering Research Center (RERC) on Hearing Enhancement in Florida. Please refer to the website: http://www.hearingresearch.org/ross.htm. Also refer to: http://www.hearingresearch.org/Dr.Ross/ANL.htm.

ANL Procedure:

1. Speech is presented (an audio book for example) to the patient to establish his/her most comfortable level (MCL).
2. Once the MCL is established, speech is played at the established MCL level in the presence of background noise. The background noise is adjusted in level to determine the point at which the background noise can no longer be increased in level and is considered "tolerable" to the patient.
3. The ANL is calculated by calculating the difference between the tolerable noise level and the MCL. 

The ANL value provides understanding of the patient's ability to tolerate background noise. The higher the ANL value the poorer the patient's ability to tolerate background noise. The lower the ANL value the better the patient's ability to tolerate background noise. The ANL value cannot be used to predict a patient's ability to understand speech in noise. Refer to Figure 184 to see the screen used for ANL measurements in the ACAM System software. 

Figure 184: Screen to measure ANL in the ACAM System