Alternative Architecture mode (ALT_ARCH)

The Alternative Architecture mode, when enabled, improves Echo Cancellation performance in reverberate environments. It operates by re-configuring the audio pipeline by switching out either the Acoustic Echo Canceller (AEC) or the Interference Canceller (IC), depending on the energy in the AEC reference signal, to recover resources for use by the rest of the pipeline.

The two audio pipeline configurations are summarised below:

  • ALT_ARCH disabled ALWAYS apply echo-cancelling AND interference cancelling; or

  • ALT_ARCH enabled apply ONLY echo-cancelling when a reference signal is available, otherwise ONLY apply interference cancelling.

The figure below expands the implementation details of the alternative mode switching. Multiplexers permit the AEC and/or the IC to be bypassed. When bypassing the IC, the XVF3610 reconfigures the AEC to use a single channel which results in the AEC cancelling echos received later in time. An internal module which collects statistics about the reference is used to dynamically control these multiplexers and memory allocation during runtime.

NOTE: Manually bypassing the IC using the Control Interface does not apply the memory reallocation.

The figure below highlights the audio signal path when the Alternative Architecture is disabled (ie. standard operation).

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Fig. 27 Audio pipeline configuration, [ALT_ARCH=0] mode

Whenever ALT_ARCH=1, then the pipeline dynamically switches between AEC alone, or IC alone. In this condition the AEC is able to make use of additional memory increasing the echo cancelling period, and making it more resilient to echo in highly reverberant conditions.

../../../_images/image26.png

Fig. 28 Audio pipeline configuration, [ALT_ARCH=1] when reference signal is present

The dynamic switching uses statistics collected from the reference signal to establish if echo cancelling is required.

../../../_images/image27.png

Fig. 29 Audio pipeline configuration, [ALT_ARCH=1] when reference signal is absent

The following table summarises the audio characteristics for standard and alternative architectures.

Table 38 Alternative pipeline mode characteristics

Pipeline configuration

Far-end audio (AEC Ref) status

Pipeline functionality

AEC characteristics

ALT_ARCH = 0

With and without Far-end audio present

IC enabled
AEC enabled

Max echo delay = 150ms

ALT_ARCH = 1

No far-end audio

IC enabled
AEC disabled

No cancellation

ALT_ARCH = 1

Far-end audio present

IC disabled
AEC enabled

Max echo delay = 225ms

The following table describes the configuration parameters for the Alternative Architecture.

Table 39 Alternative pipeline mode characteristics

Command

type

Value

Description

SET_ALT_ARCH_ENABLED

uint32

[0,1]

Enable or disable alternate architecture (alt arch)

0 - Alt arch is disabled

1 - Alt arch is enabled

When alt arch is enabled, the system works in either AEC mode (when far end signal is detected) or IC mode (when far end signal is not detected). When in AEC mode in Alt arch, AEC processing happens on only one Mic channel with 15 phases per mic-ref AEC filter.