UWB AEC is not often used in speech applications Ultra-wide band (UWB) uses a sampling rate of 32 kHz (16 kHz bandwidth). The documentation and example projects are all wide band and are implemented in this way. However, a wide band implementation can be constructed using two narrow band blocks, one for the lower frequencies and one for the upper frequencies. The base implementation of SigmaDSP is narrow band. This is the most commonly used implementation for new products, and is the implementation documented below. Wide band (WB) uses a sampling rate of 16 kHz (8 kHz bandwidth). This is the bandwidth historically used in telephony (PSTN). There are three widely accepted bandwidth standards: Narrow band (NB) uses a sampling rate of 8 kHz (bandwidth of 4 kHz). As such, the bandwidth is reduced to minimize processing resources. Most AEC implementations, including this one, are optimized for speech. The noise reduction block has use in many applications, however, that do not requires AEC. The noise reduction block also operates in the frequency domain and can follow the residual echo suppression in the block/frequency domain space with no additional overhead. While not formally part of the AEC algorithm, they are used together more often than not. However, the RES block is, strictly speaking, optional.Īn additional block, noise reduction, is also shown in the diagram below. The residual echo removal improves the performance substantially, and all performance benchmarks have been made using the two blocks together. A second block (RES) runs in the frequency domain and supplements the primary AEC block by performing nonlinear processing on the residual echo signal. operates in the stream processing domain and performs most of the functionality. The primary block (AEC) removes the linear portion of the echoes and reverberation. There are two blocks that, together, comprise the Acoustic Echo Cancellation algorithm as implemented on the SigmaDSP.
Both the voice of the remote speaker and the music will be removed from the signal picked up by the microphone, and only the local speaker's voice will be sent on the far end out.
#Acoustic echo cancellation usb mic driver
Continuing the example above, if a driver is listening to music while talking on the hand-free, the music does not need to be paused during the conversation.
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This allows full duplex conversation while music (or any known signal) is playing in the near end space. The music will be cancelled by the adaptive filter along with the signal coming from the far end. For example, if music that is playing in the near end space, it may be added to the far end input signal. The adaptive filter in the AEC block will remove any signal that is part of the far end in. This is absolutely necessary for clear, full duplex conversation over communication channel.
The person at the far end hears only the local talker and not the echoes and reverberation from the far end in the near end space. For example, in the case of a hands-free system or speakerphone, adaptation pauses when a person speaks directly into the microphone. This allows sounds in to be added to the far end out. The filter pauses adaptation when it detects sounds in the acoustic path unrelated to the far end in. The signal is then (optionally) passed through a noise reduction function to produce the output, which is a known as the “Far End Out.” This signal is sent to a Residual Echo Cancellation block (RES) that further recovers the input signal. The AEC block also calculates a residual signal containing nonlinear acoustic artifacts. The output of the filter is then subtracted from the acoustic path signal to produce a “clean” signal output with the linear portion of acoustic echoes largely removed. The algorithm continuously adapts this filter to model the acoustic path. The AEC block is based on an adaptive FIR filter. The acoustic path consists of an amplifier/loudspeaker, an acoustic environment, and a microphone returning the signal to the DSP. As shown in the diagram below, the sound coming from the remote person speaking, known as the Far End In, is sent in parallel to a DSP path and to an acoustic path. The Acoustic Echo Cancellation (AEC) block is designed to remove echoes, reverberation, and unwanted added sounds from a signal that passes through an acoustic space. Click here to return to the ADI Algorithms page
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