Included in the feature set for CDR Pro is the ability to record the Asterisk MES (Media Experience Score) for calls. The MES quantifies the audio quality for a specific call, and makes that value available to the administrator as part of the call record. FreePBX requires Asterisk version 20 or higher in order to see the MES features. To update your Asterisk version, see this wiki page:

Changing Major Asterisk Versions on the Fly