Brands:

• AMX
• BSS Audio

Models:

• AVX Architect

Overview:

This article explores the VIRTUAL view of AVX Architect and looks at the Acoustic Echo Cancellation (AEC) object. 

To see a video of this article, click HERE.

Description:

AEC basics and what some of these terms mean is covered in the article: AVX Architect - What is Acoustic Echo Cancellation [AEC]?​

The AEC object is found in the VIRTUAL view, under the Conferencing section of the audio processing objects. Adding AEC to the VIRTUAL view will create two object blocks; the AEC and Reference Return blocks.

The AEC block is connected to a microphone signal early in the signal chain, before any other processing.

The AEC Reference Return object is for the reference signal, or the signal that will be removed by the AEC processing from the signal path. The reference signal should be taken from as close to the output as possible to provide the AEC algorithm with the most accurate representation of the signal.

The PROPERTIES pane displays the typical Object Name, Workspace coordinates [location of the object is on the canvas], and DSP Allocation settings [which DSP the object is in].

The options section contains the AEC processing object options and is shared between the AEC and Reference blocks. Notice how when I select one of the objects, the other's outline will turn to a dotted line to indicate they are together.

In the OPTIONS section, we can change the channel count. The 256p has a max of 80 channels and the 512p has a max of 160 channels for AEC processing.

The Mode option will change the number of references. The default is Multi Reference, and each channel of the AEC will have its own reference signal. In Single Reference mode, all of the AEC channels will use the same reference signal.

Tail Length [in milliseconds] is selectable 100, 200 & 400. 200ms is the default.

The factory panel contains all the parameters for controlling the AEC object.

The AEC button enables or disables the AEC processing for each channel. When enabled, the AEC will remove acoustic echo from the channel with linear processing and with a specified amount of non-linear processing.

The ERL, or Echo Return Loss meter is a measure of the room's natural attenuation of the far-side audio as it leaves the speakers and re-enters the microphones. The AEC algorithm will only be able to recognize and remove echo to its best extent when this meter is in the 'green range" below 0db, so proper gain structure is critical for AEC performance. The algorithm will continue to converge over 0db, but the convergence rate will decrease in that range. If the ERL meter is over 10db, Convergence should not be expected. This meter is updated based on far-side speech only, and will not update during double-talk.

The ERLE, or Echo Return Less Enhancement meter, measures how much acoustic echo is being removed from the signal path. A lower signal indicates more echo being removed, so the lower the meter, the better.

NC is additional noise-cancellation. This setting will determine the amount of noise cancellation applied to each channel. It's a very advanced algorithm that will remove steady-state noise, like projector fan or HVAC noise, without compromising the quality of speech and intelligibility.

The non-linear processing [NLP] setting determines the amount of non-linear noise suppression that will be applied in conjunction with the AEC algorithm for each channel. NLP will remove the residual echo not removed by the linear part of the AEC algorithm. This parameter represents a trade-off between achieving good double-talk performance, with no suppression of the local speech signal, and very robust echo suppression, with no echo audible on the far side. At its most aggressive setting of 100%, the non-linear processing will remove any residual far-side echo picked up by the microphone. However, this is done with an increased risk that some near-side speech will be degraded as well, especially during double-talk. At its least aggressive setting of 0, the non-linear processing is effectively disabled, which may let some echo through, but will allow for a more natural double-talk performance. The best setting for this parameter may depend on several factors, including acoustic properties of the room and user preference. The default value of 50% may give a good balance between these objectives.

Signal Threshold is a threshold for an additional gate on the channel. In a conferencing system, some microphones may have a mute or push-to-talk feature built-in. If a mic mutes or unmutes, the characteristics of the conferencing system can change instantly, causing echo to leak through as the AEC re-converges. Using the threshold, a level can be defined that is below the normal, ambient noise floor of the room. If the mic level goes below this level, then the AEC algorithm will treat the microphone as muted, and minimize any echo that would have occurred otherwise.

The Active LED indicates that the microphone level is over the threshold, and the mic is not treated as being muted. Here's a quick way to set the threshold. First, put the microphone in its muted mode. Then set the threshold to a level where the LED turns itself on and off randomly. Raise the threshold from this level by 3 to 6db. The LED should now be off with no flickering. Take the mic out of its muted mode, and the LED should illuminate, showing it over the threshold and not being treated as muted. This process may need to be repeated if the mic's preamp gain is adjusted. Setting the threshold value to minimum will disable the mute feature.​