One of the key features on DSP units is Acoustic Echo Cancellation (AEC). This feature is not usually found in other types of mixers, and is an absolutely essential function in some situations. AEC is required when a system is used for two-way conversations between locations such as commonly occurs during audio-only phone calls and videoconferences.
Imagine you are at home on the phone talking to a bunch of people sitting in a conference room at their office. When they talk, their microphones pick up their voices, send that through the DSP, out the DSP telephone jack into the phone line, then through the phone line to your house, where you hear them talking loud and clear. Then you have something to say. When you talk, your voice goes through the phone line to their office, into the phone input on the DSP, then out to the amps and speakers in their conference room. The sound of your voice bounces around the room for a fraction of a second and is then picked up by the microphones in the conference room. Your voice is then sent back through the DSP and the phone line to your telephone.
This creates a very distracting and extremely annoying echo of your own voice that you hear every time you talk. This is where AEC would step in. AEC compares the audio coming through the microphone inputs on the auto mixer with the far-end audio coming out of the speakers. AEC then removes the far-end audio from the audio being sent back through the phone line. No more echo. In short, no AEC = poor conference calls, videoconferences and web conferences. AEC is a feature that can add significantly to the cost of a DSP, so if your client doesn’t need it, don’t get it. But if you might need it, then it is a “must have” feature.