26.1323GPPRelease 18Speech and video telephony terminal acoustic test specificationTS
Digital headsets that are connected via Bluetooth to electrical interface UE may perform speech signal processing such as equalization, automatic gain control, noise reduction and/or echo cancellation on its own. These types of headsets are often equipped with higher signal processing capabilities and the electrical interface UE should then deactivate its noise reduction and echo cancellation functions to avoid possible tandem signal processing.
The tests described in the following clauses apply only for the electrical interface UE of type Bluetooth. Their intention is to detect the absence/presence of certain signal processing functionalities in the electrical interface UE that are intended to be deactivated in case certain flags and commands are signalled by the reference interface.
For Bluetooth connections, certain commands and flags are available in the communication protocol stack of the hands-free profile. When a connection between electrical interface UE and reference interface (see clause 184.108.40.206) is established, the following two commands according to  shall be configured accordingly by the reference interface:
1) AT+BRSF (Bluetooth Retrieve Supported Features): this command may be used from the UE to discover signal processing capabilities of the connected headset or reference interface. The answer to this request shall set bit 0 to 1, which indicates that the connected reference interface provides signal processing capabilities.
2) AT+NREC=0 (Noise Reduction and Echo Canceling): this command shall be executed from the reference interface to the electrical interface UE. According to the Bluetooth specification , it is expected that the electrical interface UE disables its own signal processing