Sometimes the most frustrating thing about a conference call can be the technical glitches that prevent a meeting from reaching its full productivity potential. Bad audio can quickly derail an otherwise smooth exchange and leave participants feeling distracted and frustrated.
Echo can be a primary culprit. There are two types of echo: line echo, which is easily correctable, and the much more challenging problem of acoustic echo. Line echo is a product of reflections down the phone line, and telephone hybrids usually successfully handle that problem. But acoustic echo created by microphone-speaker coupling demands a more robust solution.
Acoustic echo happens in a conferencing environment where microphones and speakers are being used in close proximity. When the speaker on the near end is active with far end audio, near end microphones can pick up that audio and recirculate it, creating echo.
The fix for this is Acoustic Echo Cancellation (AEC). AEC is an effective way to prevent the recirculation of reflected sound waves in a conferencing environment, and the technology is quite remarkable. In brief, an AEC samples audio from the far side as it comes in and compares it to audio from inputs on the near side. If any of the audio matches, it immediately removes it by creating adaptive filters to prevent echo. This is powered by an algorithm that handles comparing and cancelling almost instantaneously, and represents an accomplishment that requires a significant amount of digital signal processing.
If you want a high-quality conferencing system, AEC is a necessity. It’s either use a powerful AEC, or give up on the idea of having a normal two-way discussion because the only way to prevent echo without an AEC is to make sure the local mics are off when the far end is talking. You need AEC for any conferencing system, even if it is teleconferencing with just one local room mic and speaker. Any time a mic and speaker are used, only AEC can provide full duplex (two-way) communication without echo. Also, most video conferencing codecs provide minimal AEC but we typically recommend that if you’re going to be using more than two microphones – some will say more than one – you need an outboard AEC with more features and more processing power. In particular you should look for a digital signal processor (DSP) that can do per mic cancelling. A separate AEC algorithm for every mic is a very effective way to control acoustic echo, even in very large rooms. We’ve seen systems that can handle more than 100 microphones.
An AEC system has to be tuned to the individual requirements of the room and the sound system components it’s going to be handling. Essentially, no two AECs will be configured the same way, and only an experienced integrator can properly program the AEC and configure the gain structure.
In my next post on AEC, I’ll discuss how an integrator is a vital part of acoustic echo cancellation.