Amplitude Normalization
Because the exact transmitted (over-the-air) level from the Source DUT devices depends on a number automatic and manual analog and digital gain settings, and because the system needs to determine deviations from expected levels, Frontline’s Audio Expert System provides a mechanism for automatic level normalization. Normalization is the process of adjusting measured level to account for known gain or loss within the system.
The Test ID Terminator Tone plays a key role in this normalization process. All Test ID tones (in Frontline’s Reference Audio files) are generated at -3 dBFS, a maximum sample value of 23196 for 16-bit resolution. When a Test ID is validated, and the system transitions into Referenced Mode, the measured amplitude of the Test ID Terminator Tone is used to calculate a normalization gain factor. This is the amount of gain required to adjust the measured level of the received audio to -3 dBFS.
This normalization gain is then applied to measured levels before comparing them to expected levels. As an example, if the Test ID Terminator is received at -5 dBFS, 2 dB below the expected value, then the “Normalization Gain” is +2 dB. A subsequent tone scripted at -12 dB, but actually received at -14 dB, would be increased by 2 dB to -12 dB before comparing it to the -12 dB value in the script, and would therefore be accepted as a correct level.