Bluetooth audio enabled devices provide high quality audio with portability. However, performing full duplex audio communications with Bluetooth devices introduces additional signal processing challenges, mainly for the acoustic echo cancellation (AEC) software. BT devices introduce echo delay path and echo response variations not present in wired systems.

Bluetooth Audio and Echo Cancellation: Delay Considerations

For wired full duplex devices, the loudspeaker and microphone positions are driven off of the same clock, and their relative positions are fixed, the echo delay path is stationary. This is ideal for AEC as the location of the echo is known, and the adaptive filter only needs to learn the echo impulse response from the loudspeaker to the microphone. Full duplex systems utilizing BT, the DAC and ADC of the loudspeaker and microphones are not driven off of the same clock. Any difference in the clock rates will result in drift of the echo path. To the AEC, this will appear as though the echo is moving, making it difficult for the adaptive filter learn the echo response. Also, due to the portability of the Bluetooth device, the user may decide to move the BT loudspeaker to another location within the room. This changes the physical distance, the echo delay and response between the loudspeaker and microphone.

Therefore, a great AEC solution must include an adaptive filter with fast reconvergence properties, and an echo delay compensation module. The echo delay compensation software continuously monitors and adjusts the echo delay parameters of the AEC.