CEA-CEB21 recommends the actions ATSC receivers with a single audio decoder should take in the presence or absence of AC-3 audio metadata carried in ATSC standards-based broadcasts. These services are defined in the ATSC references shown in the References section. CEA-CEB21 includes recommendations and suggestions on how these receiver actions should interact with user selections via different implementation choices. CEA-CEB21 is in no way intended to prohibit consumer device manufacturers from including additional features, and CEA-CEB21 should not be interpreted as recommending an upper limit to device performance.

CEA-CEB21 provides recommendations to manufacturers to facilitate user setup of audio features in the receiver without professional assistance. This bulletin provides guidance in the following areas for the reasons listed below:

• One purpose of the bulletin is to describe recommended receiver behavior in the presence of the minimum required audio metadata described by A/53.

• Another purpose of the bulletin is to describe recommended receiver behavior in the presence of additional optional audio metadata described by A/53.

This document is organized by first providing descriptions of the key metadata elements and the structural locations in the MPEG-2 Transport Stream (table sections, descriptors, etc.). The recommendations for using this information along with user settings to control audio stream selection are then provided.

Manufacturers are encouraged to develop and deploy updated firmware when practical to follow the recommendations of this bulletin.