Complete Communications Engineering

The advancement of the computing power in digital signal processors and the increased available throughput of Internet connections has made application of the high-definition(or wideband) audio communications feasible. Acoustic echo cancellation (AEC) is a critical component of wideband audio teleconferencing. The presence of the acoustic echoes in the microphone signal cause significant degradation in the quality of conversation, thus negating the benefits of having wideband audio.

The transition from standard 8kHz audio to 16kHz audio presents two additional challenges to echo cancellation. The first challenge is the length of the adaptive filter is effectively doubled. Therefore, the computational complexity of the system will be at least double. For example, the order of computational complexity of the normalized least means squares algorithm is O(2L), where L is the length of the adaptive filter.

The second challenge of performing echo cancellation with wideband audio is the increased spectral dynamic range of the excitation signal. This is because high frequency components are more easily attenuated than lower frequency components. As described in Subband Acoustic Echo Cancellation, the convergence speed of the LMS type is inversely proportional to the spectral dynamic range, thus a reduction in convergence speed is expected.

VOCAL’s engineers have developed a variety of echo cancellation modules and solutions, and have developed an echo cancellation solution to mitigate the challenges presented wideband audio. Like all of VOCAL’s software libraries, the Acoustic Echo Cancellation is available in a variety of forms, including optimized ANSI C and assembly language optimized implementations for leading DSP architectures (including but not limited to processors from TI, ADI, AMD, ARM, MIPS, CEVA, LSI Logic ZSP, etc.). These libraries are modular and can be executed as a single task under a variety of operating systems or standalone with its own microkernel.

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