What Is AEC?
AEC is an audio processing effect found in Digital Signal Processors (DSPs) that are designed for audio conferencing, when there is a room with microphones and loudspeakers on the “near side” of a phone or online call as well as someone at the “far side.” The goal of AEC technology is to remove what’s referred to as “acoustic echo,” a byproduct of performing an audio call in a room with microphones and loudspeakers.
Tonmind IP Ceiling Speaker SIP-S01M has built-in MIC, thus it supports two-way communication. It has applied AEC to remove acoustic echo.
What is acoustic echo and why does it need to be cancelled?
Acoustic echo occurs in a conferencing system when the far-side speech played in local loudspeakers is picked up by microphones in the near-side room and is transmitted back to the far side. This transmitted signal is a delayed version of the original, which causes the echo.
The received far-side signal does not transfer directly from the speaker to the microphone, but is subject to the artifacts of the room. This may include differing signal paths causing reverb, frequency filtering and attenuation. These effects are the result of the transfer function of the room. This transfer function is also dynamic as objects in the room move or the microphone moves position.
To subtract the unwanted signal correctly, the Acoustic Echo Cancellation (AEC) processor needs to simulate the dynamic room transfer function. It can then apply that transfer function to the received signal and correctly subtract the modified original signal.
Each Soundweb London AEC input card consists of four AEC input channels.
Tonmind SIP Paging Adapter SIP-T20 has interface of MIC, thus it can support two-way communication. We plan to add AEC in the future to remove acoustic echo.
How Does AEC Work?
The echo cancellation process works as follows:
1.A far-end signal is delivered to the system.
2.The far-end signal is reproduced.
3.The far-end signal is filtered and delayed to resemble the near-end signal.
4.The filtered far-end signal is subtracted from the near-end signal.
5.The resultant signal represents sounds present in the room excluding any direct or reverberated sound.
The primary challenge for an echo canceller is determining the nature of the filtering to be applied to the far-end signal such that it resembles the resultant near-end signal. The filter is essentially a model of speaker, microphone and the room's acoustical attributes. Echo cancellers must be adaptive because the characteristics of the near-end's speaker and microphone are generally not known in advance. The acoustical attributes of the near-end's room are also not generally known in advance, and may change (e.g., if the microphone is moved relative to the speaker, or if individuals walk around the room causing changes in the acoustic reflections). By using the far-end signal as the stimulus, modern systems use an adaptive filter and can converge from providing no cancellation to 55 dB of cancellation in around 200 ms.
Until recently echo cancellation only needed to apply to the voice bandwidth of telephone circuits. PSTN calls transmit frequencies between 300 Hz and 3 kHz, the range required for human speech intelligibility. Videoconferencing is one area where full bandwidth audio is used. In this case, specialized products are employed to perform echo cancellation.
Because echo suppression has known limitations, in an ideal situation, echo cancellation alone will be used. However, this is insufficient in many applications, notably software phones on networks with long delay and meager throughput. Here, echo cancellation and suppression can work in conjunction to achieve acceptable performance.
Tonmind SIP PCB Board SIP-K20-M and SIP-K20C-M have interface of MIC, thus it can support two-way communication. We plan to add AEC in the future to remove acoustic echo.
