Wireless technology has made enormous strides in terms of its reliability and flexibility for audio playback applications over the last several years. The use of wireless audio devices is highly desirable because it allows you to quickly move the location of the audio device without the need for rewiring. There is an increasing number of wireless audio devices that incorporate both a loudspeaker and microphone in the design, allowing for the devices to be used as a speakerphone for telephone calls. The full duplex audio works well on devices that have the microphones and loudspeakers enclosed into a single audio device. Standard acoustic echo cancellation (AEC) software can be applied in these devices to remove echoes causes by the acoustic coupling between the loudspeaker and microphone.
In some applications, it is desirable to have an architecture that uses separate microphone and loudspeaker devices. Developers of such systems need to know that standard AEC software will not work properly due to the lack of synchronization between the loudspeaker and microphone. There are two main issues: clock drift and packet loss. Since the loudspeaker and microphone sampling clocks are not driven by the same crystal, this leads to differing sampling frequencies and a clock drift between the devices. Left untreated the acoustic echo will be frequency shifted and appear to be moving, not allowing the adaptive filter of the AEC to properly converge. Loss packets can reek havoc on AEC software if the software cannot be made of aware of the occurrence of the lost packets. For example, a loudspeaker packet is sent out to be played, but is lost and never gets played out, the AEC will still be expecting to see an echo of that packet, which could potentially lead to the adaptive filter to diverge. Therefore, a mechanism needs to be created to inform the AEC of any loss packets, so adaptation can be halted.
VOCAL Technologies, Ltd. has developed clock drift compensation software for their AEC software, and can work with system architects to develop a mechanism in which to better handle the occurrence of lost packets in wireless communications systems. Please contact us to learn more.