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Eliminating acoustic echo

  • Article

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2, Windows Server 2008, Windows Server 2008 R2, Windows Server 8 Beta

Eliminating acoustic echo

Acoustic echo is a common problem with audio conferencing systems. It originates in the local audio loopback that occurs when your microphone picks up audio signals from your the speaker, and sends it back to the other participant along with your voice. The other participant hears this echo of his or her own voice as he or she speaks. For example:

  1. Alice and Bob are participating in a call or conference.

  2. Alice speaks into her microphone.

  3. Bob hears Alice's voice played by his speaker.

  4. Bob's microphone also picks up and transmits Alice's voice.

  5. Alice can now hear an echo of her own voice, with a slight delay due to the round-trip transmission time.

Acoustic echo can be caused or exacerbated when very sensitive microphones are used, speaker volume is turned up very high, or the microphone and speaker are very close to one another. Besides being annoying, this can prevent normal conversation among participants in a conference.

Eliminate echo with audio headsets

One of the easiest ways to completely eliminate acoustic echo is to use audio headsets. These play audio at low volume very close to a conference participant's ears. This prevents the microphone from picking up the audio signal.

Many different audio headsets are available to use with personal computers. These have connectors designed to fit into the audio jacks on sound cards. Many also have built-in microphones that enhance audio quality by staying a constant distance from a person's mouth, even while one moves or changes position.

Eliminate echo with acoustic echo cancellation

In Windows XP and Windows Server 2003 operating systems, TAPI 3.1 provides support for acoustic echo cancellation (AEC). During the process of AEC, a digital signal processor electronically compares the speaker signal to the microphone signal, and then subtracts the speaker signal from the microphone signal. In this way, AEC prevents the speaker sound from being fed back into the microphone and transmitted as an echo.