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In the audio field, AEC stands for Acoustic Echo Cancellation. It is a crucial signal processing technology widely used in bidirectional full-duplex audio communication. Its core purpose is to eliminate the echo that interferes with communication, ensuring clear audio transmission. Here is a detailed breakdown:

Key Performance IndicatorA common indicator to measure AEC performance is Echo Return Loss Enhancement (ERLE). Generally, a qualified AEC system needs to achieve an ERLE of no less than 40dB. Advanced systems can even achieve echo cancellation of up to 55dB within about 200ms, which is sufficient to meet the needs of most daily and professional communication scenarios.

The Cause of Echo It AddressesDuring two-way calls such as video conferences or hands-free calls, the sound from the far-end speaker is played through the near-end speaker. This sound will be picked up by the near-end microphone—either directly or after being reflected by walls, furniture and other obstacles in the environment—and sent back to the far-end. As a result, the far-end caller will hear their own delayed voice, which is the acoustic echo. AEC targets this problem that only arises in full-duplex communication (where both parties can speak and listen simultaneously). In half-duplex communication like walkie-talkies, this echo issue does not exist.

Core Working PrinciplesThe key to AEC lies in adaptive filtering algorithms. First, it takes the audio signal from the far end (also called the reference signal, which is the source of the sound played by the near-end speaker) as a reference. Then, it simulates the acoustic transmission path of the near-end environment (including the characteristics of the speaker, microphone and the reflection effect of the room) through an adaptive filter to estimate the echo signal that the near-end microphone will collect. Finally, it subtracts this estimated echo signal from the actual audio signal collected by the near-end microphone, so as to obtain a clean target voice signal. The adaptive filter can continuously adjust parameters according to changes in the environment, such as the movement of the microphone or people walking in the room, to cope with dynamic changes in the echo path.

Common Classification of Echoes ProcessedAEC needs to handle two types of echoes with different characteristics in practical applications:

Direct Echo: Also known as linear echo. It refers to the sound from the near-end speaker that is directly collected by the microphone without reflection. Its delay is easy to estimate because it is only related to the distance and position between the speaker and the microphone.

Indirect Echo: Also called non-linear echo. It is the sound from the speaker that is collected by the microphone only after multiple reflections in the environment. Its intensity and delay are affected by the room layout and obstacle distribution, and it is more complex to process due to its dynamic variability.

Typical Application ScenariosAEC is widely used in various audio communication devices and systems. For example, video conferencing equipment such as Huawei Ideahub, hands-free car phone systems, smart speakers, IP intercoms, and video call software like Zoom. It can also be integrated into audio processing chips and SDKs, adapting to different sampling rate requirements and hardware platforms such as ARM and Intel.