Where to find acoustic echo cancellation
Networks can introduce in excess of 100msec of delay and this combined with processing delays would make it necessary to have an echo canceller for smoother, full-duplex conversations. An echo during telephonic conversations is a result of network and processing delays. But delays greater than 40ms would be perceived as an echo by human ears. Delays less than 40ms (for speech) are usually safe and would not annoy the listener. Now would be a good time to understand how different delays of echo affect the human ear. Thus, NLP would be required after the LAEC stage in a speech processing chain to effectively suppress the echo. Since there would be no linear relation between the actual far-end and the captured echo because of the non-linearities of the device, LAEC would not be able to predict the far-end for non-linear echo suppression. The linear adaptive filter mainly works to adapt the predicted signal to match with the direct path echo and all the other echo paths, in most cases, along with non-linearities added by the device (vibrations, etc.), they are removed by Non-Linear Processing (NLP). Echo in the microphone captured signal is the result of a direct path (which is influenced by the distance between the microphone and loudspeaker and their look-direction) and multiple reflections from surrounding walls or objects. The error difference is fed to the adaptive filter so that the filter can adapt itself and produce predicted echo, using the far-end signal, which closely matches the echo captured by microphones.Ī good AEC would have a good adaptive filter which produces a predicted far-end that matches very close to the echo captured in microphone signals so that the error difference is less.
#Where to find acoustic echo cancellation free
The basic principle of any Linear AEC is to predict the far-end signal (x(n)) by using an adaptive filter and then subtract the predicted far-end signal (ŷ(n)) from the microphone signal (d(n)) to generate the error signal (e(n)) free of the far-end signal. Let's dig deep into how Echo Cancellation works. AECs can be further classified into linear and non-linear. And AECs are used to cancel out the echo resulting from the acoustic coupling between microphones and loudspeakers. LECs are used by telephone networks to cancel echo resulting from the coupling between networks. Line Echo Cancellers (LEC) and Acoustic Echo Cancellers (AEC). But for an uninterrupted and natural conversation, full-duplex communication is required and an Echo Canceller is a must in this scenario. A typical example of such communication is the Walkie-Talkie. While one party speaks, the other party listens and vice versa. In half-duplex communication, transmission is unidirectional at any moment during a conversation. Having understood echo, the easiest way to avoid it is by using half-duplex communication. Echo is not always an issue in the case of speakerphones but also on mobiles and other handsets because of the mechanical coupling of earpiece speakers and microphones. Hence, we need to have a mechanism to block the transmission of far-end back to the other party in the call, which is accomplished by using an Echo Canceller in a communication device. Conversations in such scenarios would be very annoying and non-intelligible. The amount of delay defines how annoying the experience could be. Echo is the phenomenon where one hears his/her own voice after a certain delay. If the far-end speech gets transmitted back to the other side of the call, then the other person would hear their voice after some delay (network + processing delay). However, the microphones also capture the far-end speech due to the acoustic coupling of the loudspeaker and microphone. And your own voice, referred to as near-end speech, would be captured by the microphone and sent across the network to the other end of the call. The speech of the other person you are talking to, referred to as far-end speech, would be played out from the loudspeaker. Suppose you are in a voice call talking with someone over a speakerphone. Let's first understand what echo is in terms of voice communication.
#Where to find acoustic echo cancellation series
AEC is not only present in cellphones but also in all kinds of audio calling devices like Amazon’s Echo series and Facebook’s Portal devices. Echo cancellers aid for smooth and intelligible conversations in full-duplex voice communication. Research on Echo cancellers started in the 1960s, especially for voice communication devices. Acoustic Echo Canceller (AEC) plays an important role in voice communication systems.