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Biamp Systems

Tesira TCM-series AVB Beamtracking™ Ceiling Mics

The following article is intended to provide information in regards to the Tesira TCM Series Beamtracking™ Microphones. We will discuss some of the core technologies that make these microphones work, as well as the resources available in software for setup and configuration.

Hardware overview

TCM-1       Head end plenum box + one pendant mic arrayWiring Diagram PoE+ Injector.png

TCM-1A    Head end plenum box w/built in amplifier + one pendant mic array   

TCM-1EX  Extension plenum box + one pendant mic array  

Each TCM-1 or TCM-1A can host up to two TCM-1EX extension microphones connected in a daisy chain using standard CAT5 or better cable. This means that with just a single cable run from the ceiling down to the DSP, you can have coverage from three Beamtracking  microphone arrays, which should be suitable for most small to mid-sized conference room applications.*   

There is a maximum distance of 330' (100 meters) between any head end unit (TCM-1/TCM-1A) and the AVB capable network switch. Point-to-point cabling between the TCM-1 / TCM-1A and the first TCM-1EX has a limitation of 33' (10 meters). Point-to-point cabling between the first and second TCM-1EX units has a limitation of 33' (10 meters). In all models, the supplied pendant microphone allows a maximum drop of 5 feet (1.5 meters) including any strain relief within the plenum ceiling box.

The power requirements of each device are as follows:

TCM-1        PoE (IEEE 802.3at Class 3, 15.4W)

TCM-1A     PoE+ (IEEE 802.3at Class 4, 30W)      

TCM-1EX   Power provided by TCM-1 or TCM-1A

They may be directly connected to the AVB port on a Tesira server class device using a PoE+ injector, or via a PoE+ port on an AVB capable network switch.

*When installed at a height of 8’ (2.5 meters), the TCM-1 Beamtracking Microphone maintains a STIPA A rating over a coverage diameter of 33’ (10 meters).  Room conditions at time of measurement: RT60 (@5meters) = 425ms, Noise Floor weighted = 38dBSPL-A.

Core technologies

Beamforming Animate 2.gifLet's start by taking a look at a single pendant and beamforming.

Beamforming is the ability to shape or steer a microphone array's directivity (polar) pattern.  Consider the situation where you have multiple microphones in a room, or in this case, multiple elements in an array.  Sound will arrive at each microphone with a different time delay and level decay. 

By utilizing DSP, which Biamp knows a thing or two about, we can shape the pickup pattern by compensating for the delay and level differences between microphones.  A single TCM-1 pendant has eight microphone elements working together to create three 120° zones, each with it's own steerable beam, allowing for a full 360° of coverage.

This is all well and good, but beamforming is nothing new, and there are plenty of other microphones out there utilizing this technology.  What makes the TCM series unique is that the microphones use Beamtracking  technology to analyze the signals from each microphone element in order to determine where the talker is, then passes that information on to the beamforming algorithm to tell it where to steer the polar pattern.  This is accomplished, in part, by a process called Voice Activity Tracking.  

Voice Activity Tracking

When a signal enters the TCM-1 microphone array it diverges into two paths - the audio signal that is sent over AVB to the Tesira server class device, and a signal used for tracking.  The tracking algorithm makes use of aggressive noise cancelation to ensure that noise sources in a room, such as ceiling mounted projectors and HVAC systems, do not cause the tracker to falsely trigger. VAT Diagram no border.png

It is optimized to only track signals within the frequency domain of human speech, further focusing the tracking algorithm to engage on just talkers within the room.  It then passes this information on to the beamformer which directs its polar pattern to the located talker.

The tracker will follow in both azimuth (left-right) and elevation (up-down) angles and will work independently in each of the three 120° zones.

Beam Weighting

Adding tracking capabilities to the beamforming microphone array creates a problem for us to solve.  If two beams in a single pendant track to the same talker, such as the scenario where a talker is positioned between two coverage zones, it could introduce comb filtering, or other phasing issues.  To combat this, we implemented the concept of beam weighting.  When two beams are directed to the same talker, each signal is analyzed and the stronger signal is selected. 

Beam weighting stops the phasing issues that could occur from two beams tracking to the same signal.  However, when the signals are different, such as when two people are talking, it does not stop multiple beams from being used to properly pick up talkers across multiple coverage zones. This processing takes place within the TCM-1 plenum box.

Intelligent Mixing

Auto Mixer Init Dialog.pngBeam weighting addresses the issue of single talker and multiple beams, but what about a single talker and multiple pendants.  For  this, we introduce the concept of Intelligent Mixing. 

By nature of the design, if there are two pendants in a room, they will both track to a human voice source.  Mixing intelligence, placed post tracking algorithm, allows the system to identify which pendant has the better signal and deliver that to the final mix. This only applies to a common source.  With separate signals in a room multiple pendants can still be active.

Intelligent Mixing for Beamtracking microphones is enabled within the Gating Auto Mixer block when adding to your Tesira layout.  In the Gating Auto Auto Mixer BT.pngMixer initialization dialog select "Preconfigure for Beam Tracking Mics".  This will optimize the auto mixer settings for use with the TCM-1 series microphones.  The bottom right hand corner of the Gating Auto Mixer will show "BT" as a visual indication that this option has been chosen.  Additional information pertaining to the software configuration will be discussed in the next section

AEC Interaction

Biamp's Beamtracking Microphones are ultimately designed with conferencing and collaboration in mind and you can't talk about conferencing without mentioning Acoustic Echo Cancelation (AEC).  AEC performance is one of the most, if not the most, critical processing components in an audio conferencing system.  Because Biamp has created both the Beamtracking and AEC algorithms within Tesira, both are aware of and communicate with each other to help ensure a quality meeting experience.

When the far end talks, a Beamtracking microphone will analyze this signal, identify it as human speech, and want to track to it.  However, our AEC algorithm is capable of telling the beamtracker that it is the far end who is talking and will temporarily lock the beams in place, keeping them from tracking to the far end voice coming out of the room's loudspeakers.

This interaction between our AEC and Beamtracking algorithms is patented technology that allows for the requirement of only a single channel of AEC per pendant microphone.  This scenario would typically require three channels of AEC, one for each beam or coverage zone.

Software and programming 

Adding Biamp Beamtracking Microphones to a layout is a simple process and resources have been provided to aid in the configuration.  Below we will highlight the blocks that should be included when programming as well as the options available to optimize settings for use with TCM-1 microphones.

TCM-1 I/O Blocks

The TCM-1 and TCM-1A are added to the configuration from the I/O Blocks list found under the Audio Object Bar.

 TCM Object Bar.png

 

 

 

 

 

 

Once the appropriate TCM model is selected and added to your layout, an initialization dialog will be shown.TCM Init Dialog.png  This allows you to configure the following:

  • Microphone Count 1-3 inputs depending on the number of TCM-1EX units that will be daisy chained to the head end unit.
  • Logic Inputs for LED control and muting
  • Mute multiple microphones as a group, or individually
  • Enable logic outputs that could be used to drive logic functions within Tesira based on mic mute state
  • Add or remove the amp block when utilizing the TCM-1A built in amplifier

After confirming the configuration and selecting OK, the blocks will be added to the layout.  For example, choosing a microphone count of 3 and including the TCM-1A amplifier block produces the below blocks.

TCM-1A 3 channels.png

Azimuth 3 Channel.pngThe Control Dialog for the TCM-1 Input block will display based on the number of microphones chosen.  A software representation of the azimuth tracker will be included for each microphone, as well as mute, level, height settings, and an RMS meter. 

When live with the system, the azimuth tracker will display a Red, Blue, or Green indicator, one for each beam or coverage zone, and will provide feedback for activity and tracking within that zone.

The height should be set at the measured distance from floor to microphone array.  This will affect the maximum upward angle at which the microphone will track.  A higher setting will limit the angle, keeping the beam from tracking too close to sources coming from the ceiling.  A lower setting will increase the coverage angle to accommodate talkers being nearer to the mic's 0° elevation angle.

AEC Processing Block

In most cases, a TCM-1 input will first be connected to an AEC processing block. AEC Block.png We have identified a recommended configuration for the AEC processing block when used in conjunction with a Biamp Beamtracking Microphone:

NLP = Medium

Noise Reduction = Low

AGC = Bypassed

To quickly deploy these settings, a "Preconfigure for Beamtracking Mics" option has been added to the AEC initialization dialog.  The most critical of these settings is to ensure that AGC is bypassed.  When utilizing beamtracking microphones, we want AGC to occur post auto mixer.  This AGC processing will be included automatically when adding the TCM-1 custom processing block to your layout.

TCM-1 Custom Processing Blocks

In an effort to simplify setup and deployment, software will install with a series of custom blocks preloaded into the processing library. Processing Library.png This will help limit programming time and ensure that recommended steps and settings are being followed when including TCM-1 microphones in your layout.  Each "TCM-1 Beamtracking Block" will vary by the number of channels, but contain the same processing blocks and single mixed output. 

3 Channel Custom Block.pngThe EQ is a recommended starting point for each pendant that should be applied outside of any other needed "room" EQ.

The Beamtracking Auto Mixer should look familiar.  This is where Intelligent Mixing comes in to play.  Note the "BT" in the bottom right hand corner of the block, indicating that "Preconfigure for Beam Tracking Mics" has been selected.

Before mixing the pendant signals down to the single output we pass through AGC, which has been configured to ensure the best performance and compatibility with Biamp Beamtracking Microphones.  

3 Channel Custom Block Expanded.png

TCM-1A Amplifier Block

When utilizing the TCM-1A's built in two channel amplifier, a two channel amplifier output block will be added to the layout.  From here you are provided with controls to set load impedance, level, and mute, as well as monitor the amplifier's current state. 

Of particular interest is the Burst indicator.  This is a visual indication that Burst power reserves are being utilized to handle peaks in the audio signal.

Amplifier Block.png

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