Problem | Symptoms

The AEC (Acoustic Echo Cancellation) reference signal is being passed through to the reinforcement outputs, causing unintended audio distortion. 

Causes | Verification

The AEC Sound Reinforcement outputs are intended to be used for Voice Lift applications. The AEC Reference signal contains the far end signal as well as the 'other’ mic signals. Without a far end, the reference signal contains only the ‘other’ mic signals.

Improper Application of AEC: When a signal is sent to the AEC Reference but is not played into the room and picked up by the microphones, the AEC system continues to search for and cancel out this signal. This results in the out-of-phase version of the signal bleeding into the reinforcement outputs.

Muted Microphone Channels: The AEC continuously adapts to subtract a filtered version of the reference signal from the mic signal. If the microphone signal is muted, the adaptation freezes, but the filtered version of the reference signal is still subtracted from the muted mic signal, making it audible in the reinforcement output.

Solution | Workaround

• Ensure Proper Signal Routing: Verify that the AEC Reference is only receiving the appropriate signals, which typically include any far-end conferencing sources such as a Speakerphone In component (USB Audio Bridge), VoIP In (Softphone), or POTS In component. If mics are being locally reinforced in the room, each microphone’s AEC Reference can also optionally include some or all of the other mics in the room (but no microphone should ever be sent to its own AEC Reference).
• Check Microphone Channel Status: Ensure that microphone channels are not muted if they are part of the AEC process. If a mic needs to be muted and unmuted, the muting should ideally take place after the AEC component.
• Validate AEC Reference Signal: Confirm that any signal sent to the AEC reference is actually being played into the room and picked up by the microphones to avoid unnecessary cancellation attempts.