A Real-Time Audio Tele-Presence Device for 

Remote Acoustic Monitoring 

by Michael A. Vaudrey and Sujayeendar Sachindar 

ARL-CR-0502 December 2003 

prepared by 

Adaptive Technologies, Inc. 

1700 Kraft Drive, Suite 2350 

Blacksburg, VA 24060 

under contract 

DAAD17-02-C-0055 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5425 

ARL-CR-0502 December 2003 

A Real-Time Audio Tele-Presence Device for 

Remote Acoustic Monitoring 

Michael A. Vaudrey and Sujayeendar Sachindar 

Adaptive Technologies, Inc.

Approved for public release; distribution is unlimited.
ii 

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5a. CONTRACT NUMBER 

 DAAD17-02-C-0055 

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4. TITLE AND SUBTITLE 

 A Real-Time Audio Tele-Presence Device for Remote Acoustic Monitoring 

5c. PROGRAM ELEMENT NUMBER

 622716 

5d. PROJECT NUMBER 

 AH70 

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6. AUTHOR(S) 

 Michael A. Vaudrey and Sujayeendar Sachindar (both of ATI) 

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 Adaptive Technologies, Inc. 

 1700 Kraft Drive, Suite 2350 

 Blacksburg, VA 24060 

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 ARL-CR-0502 

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 Bldg 520, Aberdeen Proving Ground, MD 21005-5425 (telephone 410-278-3529).

14. ABSTRACT 

This Small Business Innovation Research program sponsored by the U.S. Army Research Laboratory (ARL) addressed the issue of remote 

monitoring of acoustic environments with the hearing acuity a soldier is accustomed to, without placing the soldier in a potentially hostile 

acoustic environment. To achieve this goal, Adaptive Technologies, Inc. (ATI) employed a product-oriented design strategy to develop a 

wired proof-of-concept prototype using commercial-of-the-shelf components.

At the end of the Phase I effort, ATI delivered to ARL a fully functional wired binaural hearing device capable of accurately monitoring 

remote acoustic environments as far as 50 feet from the listener/operator. The remote head and ear system was mounted on a robotic 

device that permitted pan-and-tilt motion of the remote ears. The orientation of this was commanded by the local user’s head location, 

which was measured by a head-tracking device purchased from Ascension Technologies, Inc. Finally, a customizable audio path 

equalization process was created to flatten the magnitude response between the remote and local ear canal locations to ensure the highest 

fidelity and most realistic audio reproduction possible. In addition to the customizable frequency response, ATI provided ARL with a 

fixed equalization filter that was fit to a small population of users tested at ATI. This generic digital filter was designed to operate at a 

sampling frequency of 44 kHz.

The following is a summary of the technical accomplishments at the end of the Phase I effort:

 • A remotely deployable binaural hearing system was developed and delivered, which provides the ability to accurately and 

effectively monitor the remote acoustic environment.

 • A real-time control system comprising a head tracker and a robotic head was created, which emulates head movement at the remote 

location, providing the ability to quickly localize any surrounding sound.

 • Two equalization methods were developed that provide the user with more realistic audio reproduction. The customizable 

equalization and the fixed generic equalization were both delivered to ARL for testing at the end of the Phase I effort.

15. SUBJECT TERMS

 acoustic monitoring; remote microphone; tele-presence

16. SECURITY CLASSIFICATION OF: 

19a. NAME OF RESPONSIBLE PERSON

 Michael A. Vaudrey 

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OF PAGES 

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Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18
iii 

Contents 

List of Figures iv

1. Phase I Technical Review and Strategy 1

1.1 Phase I Technical Objectives and Work Plan .................................................................1 

2. Head-Tracking System 3

2.1 Hardware .........................................................................................................................4 

2.2 Software...........................................................................................................................6 

3. Armature Module 7

3.1 Hardware .........................................................................................................................7 

3.2 Software...........................................................................................................................8 

4. Command and Control Software Interface 9

5. Audio Path 11

5.1 Input and Output Scaling...............................................................................................11 

5.2 Headphone Wiring ........................................................................................................12 

5.3 Headphone Audio Path Equalization ............................................................................12 

6. Final System Design and Configuration 18

7. Conclusions 20

Appendix A. Wired Binaural Microphone: User and Instruction Manual 23

Distribution List 40 
iv 

List of Figures 

Figure 1. Wired binaural microphone system block diagram.........................................................3 

Figure 2. Quantitative analysis of the performance of 3D bird (blue) and flock of birds 

(black). .......................................................................................................................................6 

Figure 3. First generation GUI developed for the system by ATI..................................................9 

Figure 4. Simplified GUI design for the final system...................................................................10 

Figure 5. Audio signal path...........................................................................................................11 

Figure 6. Sensing microphone in the artificial ear (left) and identification micro-phone in 

the human ear (right)................................................................................................................13 

Figure 7. Equalization routine.......................................................................................................14 

Figure 8. Frequency response before (lower curve) and after equalization (upper curve). ..........15 

Figure 9. Equalizer filter for figure 7 system................................................................................15 

Figure 10. Small population of frequency responses....................................................................16 

Figure 11. Population of frequency responses from figure 10, equalized with their average 

inverse......................................................................................................................................16 

Figure 12. Population of frequency responses through EZ-kit device..........................................17 

Figure 13. Equalization filter for generic solution........................................................................17 

Figure 14. Generic equalized frequency responses.......................................................................18 

Figure 15. Command and control user interface...........................................................................18 

Figure 16. Audio path user interface.............................................................................................19 

Figure 17. Fully functional wired binaural microphone system...................................................19 

Figure A-1. 3D bird attached to headphones. ...............................................................................24 

Figure A-2. Remote acoustic sensor shown with head form and ballast weights on biclops 

and tripod mount......................................................................................................................26 

Figure A-3. EZ-kit DSP evaluation board for generic population equalization. ..........................27 

Figure A-4. Dspace analog interface box and PC.........................................................................28 

Figure A-5. Analog interface circuitry..........................................................................................29 

Figure A-6. Command and control graphical interface. ...............................................................31 

Figure A-7. Customized acoustic equalization interface. .............................................................33 

Figure A-8. Full system during operation.....................................................................................34 

Figure A-9. The local user places the microphone facing out, using the pre-fabricated 

earplugs designed for holding the microphone.......................................................................36 
1 

1. Phase I Technical Review and Strategy 

The Adaptive Technologies, Inc. (ATI) Phase I proposal clearly outlined the technical focus of 

the Phase I effort. In general, the resulting work of the Phase I effort closely matched the 

proposed tasks. This section summarizes those Phase I work tasks. 

1.1 Phase I Technical Objectives and Work Plan 

The primary purpose of the Phase I effort was to develop a fully functional, proof-of-concept 

prototype of a wired binaural microphone system to provide highly accurate remote listening 

capability. The design of the proposed binaural system consisted of three main components: the 

machine–to-soldier acoustic interface, the soldier-to-machine mechanical interface, and audio 

control features. The elements of the design process were as follow: 

1. Generate electronic signals that accurately convey the binaural localization and 

discrimination capabilities of the human hearing mechanism to a remote listener so that 

realistic audio telepresence is achieved. 

2. Develop a human-machine interface that accurately controls the orientation of the remote 

hearing mechanism in concert with the operator movement. 

3. Investigate and implement audio control features into the binaural microphone system. 

In the first month of the Phase I Small Business Innovation Research (SBIR) contract, a “kickoff” meeting was conducted at Aberdeen Proving Ground, Maryland, between ATI and U.S. 

Army Research Laboratory (ARL) personnel. The general form of the proposed design was 

agreed upon between the sponsors and ATI. The real-time head-tracking unit was received from 

Ascension Technologies, Inc., and was verified to be functioning within quoted specifications 

via the manufacturer-supplied software program. The task of designing and building the robotic 

armature module, along with the associated motor controllers was circumvented by the discovery 

of the robotic head “Biclops1” available for purchase from TRACLabs, a division of Metrica, 

Inc. The robotic head, which was developed under a separate SBIR program, was originally 

designed for computer vision applications intended to incorporate two cameras for stereo vision. 

With full pan-and-tilt capabilities, this was an ideal choice for moving forward quickly on this 

project. 

In the second month of the Phase I SBIR, the software supplied with the Ascension Technologies 

head tracker device was customized by ATI. Modifications included removal of unnecessary 

interface code (including menus and graphical displays), inclusion of smoothing code to limit 

 1

Biclops is a trademark of TRACLabs. 
2 

very small measurement anomalies in the normal functioning of the head tracker, and 

preliminary limit checking of pan-and-tilt positioning. 

The robotic head or armature module (ArM) was delivered and tested with a test program 

provided by TRACLabs. The software supplied with the head was altered for specific position 

control. A prototype of the external acoustic receptor (EAR) was constructed and mounted on 

the Biclops. Investigation into specific filter parameters and the frequency response equalization 

was initiated during the course of the second month. 

In the third month of the Phase I SBIR, a Windows2-based graphical user interface (GUI) 

application was developed in order to permit the 3D Bird3 and the Biclops to function in tandem. 

This application uses the same functions and underlying structures for the 3D Bird and Biclops 

robotic head provided by the manufacturers of these commercial off-the-shelf (COTS) devices. 

However, an entirely new application was developed that provides only the necessary 

functionality for orienting the head measurements with the head tracker and homing the Biclops. 

Real-time communication of position information from the head tracker was relayed to the 

robotic head, permitting tracked movement; in the process, several performance limitations were 

discovered that are attributable to the position measurement. Both small and large real-time 

measurement errors were apparent in the 3D Bird tracking device and were translated by the 

robotic head as head movement. 

In the fourth month of the Phase I SBIR, significant processing to the Windows-based GUI 

application was added in order to provide a fully functional, robust system, and improved 

functionality was incorporated to allow easy use. The audio path was designed and installed in 

the Biclops robotic head. A fully functional system was built, and preliminary tests to verify the 

operation of the system were conducted. Initial testing results indicated very accurate source 

localization capabilities with the first generation prototype system. A dynamic positional error 

(incorrectly interpreted as position commands by the robotic head) was caused by limited 

accuracy of the sensors in the low cost three-dimensional 3D Bird head tracker. A second source 

of position error was caused by the Biclops, wherein the digital encoder performance was being 

affected by electromagnetic interference (EMI) from the motor signal when it operated during 

high speeds. By physically separating the motor signals from the digital encoder signals, the 

manufacturer rectified this problem, and position errors attributable to this hardware design were 

eliminated. 

In the fifth month of the Phase I SBIR, refining steps were made to prepare the wired binaural 

microphone for delivery at the end of Phase I. The Windows-based GUI application was 

simplified, and improved functionality was incorporated to allow easy use. A context-sensitive 

help window was added to assist the users in using the software program. A 50-foot serial cable 

 2

WindowsTM is a trademark of Microsoft Corporation. 3

3D Bird, which is a registered trademark of Ascension Technology Corporation, is a three-degree-of-freedom 

device that measures orientation based on the output of solid state inertial and non-inertial sensors. 
3 

was used to communicate with the robotic head, and the system was observed to function 

perfectly. 

During the final month, a bracket designed to mount the Biclops on a camera tripod was 

manufactured by ATI. A head form was purchased and covered with a layer of liquid latex to 

provide a skin-like finish. A population average digital filter for acoustic path equalization was 

designed and implemented via the Analog Devices, Inc. EZ-kit portable digital signal processor 

(DSP) evaluation board. The wired path between the remote and local systems was extended to 

50 feet. In preparation for system delivery, analog anti-alias and smoothing filters for the stereo 

audio paths were designed and a user manual was created (see Appendix A). The final system 

was retested and prepared for delivery to ARL. 

The final system block diagram is shown in figure 1. 

Audio 

Processing

External 

Acoustic 

Receptor

Armature 

Module

Command 

and Control

Head 

Tracking 

System

Earphones

Psychophysical Aspect

Cortex Aspect

Physical Reflex

Artificial 

Head

Figure 1. Wired binaural microphone system block diagram. 

The dotted portion of the block diagram represents the human interaction with the system. The 

head tracker measures head movement and translates that to remote head movement. The 

external acoustic receptor delivers the remote audio signal to the user’s ears through headphones 

after processing. 

The remaining sections provide technical details for the software and hardware development of 

each component of the wired binaural microphone system, which consists of the head-tracking 

system, the remote robotic head, and the audio path. 

2. Head-Tracking System 

The head-tracking system measures the instantaneous position or orientation of the operators’ 

head. This real-time information is used to command the remote robotic head in concert with the 
4 

user’s head to simulate real-time localization abilities. Ascension Technologies, Inc.’s 3D Bird 

product is used to implement the head-tracking system. 

2.1 Hardware 

The 3D Bird is a small (1.2 ounces), head-mountable device that communicates through the RS232 port of a PC and provides real-time measurements at the rate of 160 times per second. The 

hardware unit consists of three sensors and the microprocessor that controls data acquisition and 

communication with the host PC. The manufacturer has provided a strain relief at the point 

where the sensor attaches to the cable. A minimum warm-up time of 15 minutes is required to 

allow the electronic circuitry time to equilibrate to temperature changes in order to achieve the 

highest degree of accuracy from the tracker. The sensor is sensitive to low frequency currentgenerating devices such as power cords, power supplies, and cathode ray tubes (CRTs). Their 

emanations can be detected by the sensor and converted into noise on the output orientation 

measurements. The sensor has been fixed to a piece of plastic and a secondary strain relief 

added by ATI and mounted onto the headset. The sensor cables are bundled and shielded to 

minimize noise and ensure accurate performance within specification. 

When the hardware was connected to the communications (COM) port of the host PC and the 

executable test program was run, small and large errors in the real-time measurement of the 

orientation were observed. Based on telephonic consultation with the technical support at 

Ascension Technologies, Inc., it was determined that these errors were a result of the sensors 

being used in the hardware of the head-tracking system. Ascension Technologies produces a 

number of head-tracking or real-time position measurement devices, and the 3D Bird appears to 

be the only product that exhibits such errors, both large and small. The 3D Bird contains three 

sensors that are used to measure the angular orientation of the device. Different sensors are used 

to measure the position in the static and dynamic modes. The dynamic mode uses a feedback 

algorithm that tracks angular position dynamically. However, no such algorithm is available for 

the static mode, and therefore, greater errors in position measurement are present when the 

device is stationary. In other words, even when the head tracker does not move, the measured 

value varies. Since this variation is passed onto the robotic head as position data, the head 

moves in response to the command input. This particular source of error can behave as a low 

magnitude, high frequency noise interfering with valid command signals or can become a higher 

magnitude offset in actual position measurement reaching or exceeding 20 degrees of error. The 

latter error is related to a Gaussian disturbance that affects the magnetic sensor. This problem 

was temporarily corrected with a magnetic field degausser. 

A possible solution was to take advantage of the fact that different sensors are used by the 

tracking system in the static and dynamic mode. However, the microprocessor inside the 

hardware produces only orientation information; no information from the sensors could be 

accessed. Another potential solution involves signal processing of the head tracker signal before 

it is transmitted as the control signal to the robotic head. Classical DSP techniques for noise 
5 

reduction such as filtering are complicated by the fact that the control system is not strictly a 

sampled data system executing in real time. In the Windows operating environment, non-related 

processes can cause interruptions in the head-tracking control code, which will effectively alter 

the “sample rate”. Therefore, any digital filtering could change the operation of the system in 

frequency and effectiveness. 

As an alternative, a second product to perform head tracking was considered. Ascension 

Technologies produces a number of head-tracking or real-time position measurement devices, 

and the 3D Bird appears to be the only product that exhibits such errors, both large and small. 

ATI obtained the Flock of Birds4

 product and performed a comparative study of the performance 

between the two devices. A quantitative analysis of both devices was performed to determine 

their relative performance. The 3D Bird and the Flock of Birds were placed on a wooden desk, 

in a stationary condition, with their orientations at the origin with respect to their respective 

magnetic fields (earth’s magnetic field for the 3D Bird, transmitter-generated magnetic field for 

the Flock of Birds). 

Analysis of the data streamed from both the devices provided an indication of the statistical 

nature of the noise in their data output. The data vectors were approximately 60,000 samples in 

length, corresponding to approximately 10 minutes of streamed orientation information. The 

standard deviation for the 3D Bird data was calculated to be 2.141 degrees, whereas for the Flock 

of Birds it was 0.0284 degree. A histogram plot in figure 2 indicates the distribution of the 

orientation information measured with both devices. 

The maximum deviation with respect to the origin (the actual position) was calculated to be 4.6° 

for the 3D Bird and 0.13° for the Flock of Birds. Based on this statistic, ATI concluded that the 

Flock of Birds outperforms the less expense 3D Bird device with respect to noise in motionless 

measurements over time. Based on this analysis, ATI has concluded that the Flock of Birds 

qualifies to be used as the head-tracking device for the wireless binaural microphone 

implementation. 

A careful cost-to-benefit performance analysis must be made during Phase II to ensure that the 

increased expense, complexity, and additional hardware of the Flock of Birds is warranted by the 

performance improvements. The Flock of Birds device is large, significantly more expensive, 

and requires a separate magnetic field transmitter and separate processor in addition to a PC 

connection. 

 4

Flock of Birds is a registered trademark of Ascension Technology Corporation. 
6 

Figure 2. Quantitative analysis of the performance of 3D bird (blue) and flock of birds (black). 

2.2 Software 

The head-tracking unit was received by ATI along with a demonstration application. The 

demonstration application consists of a GUI that displays the orientation information (azimuth, 

elevation, and roll), both graphically and in numeric form. The menu options for this interface 

allow the user to choose or set the COM port that the device is connected to, the data display 

format, the reference angles for the three axes, the filter scale value (1 to 10) that rounds the 

fractional/miniscule variations in orientation data, menus to start, stop, and reset orientation of 

the 3D Bird, and data logging. Although nice features, many of these functions are not required 

for the wired binaural microphone application. 

ATI modified the associated source code for this executable program to operate with a specific 

COM port, filtering scale, and data display format. The menu options were removed from the 

GUI to reflect this step. The graphic display of the azimuth, elevation, and roll axes was 

removed along with the data-logging facility. The corresponding source code for these was also 

removed. This results in a smaller and more manageable code, accomplishing only the features 

needed by this specific application. Although the graphical display of the head tracker 

orientation was removed, textual monitoring of orientation data was maintained for troubleshooting purposes. In addition, the source was modified to indicate when the head tracker turns 

by more than ±165° along the pan/azimuth axis with respect to its initial orientation. This is 
7 

required since the Biclops robotic head has a pan/azimuth limitation of ±165°. Likewise, a tilt or 

elevation that exceeds ±60° can also be detected. 

A new application was created with Microsoft Visual C++5 that establishes communication with 

the 3D Bird and streams the real-time data, displaying the azimuth and elevation data in edit 

boxes. This program allowed the user to reset the orientation of the Bird and displayed the status 

of the link through the COM port between the host PC and the 3D Bird. When the orientation 

data are streamed, the code checks for the range of the angle data and then displays the value in 

the edit boxes. This program, with minor modifications, would be added to the portion of the 

software that communicates with the Biclops armature module. 

3. Armature Module 

As was discussed with the contract sponsors, the customized armature module envisioned for the 

Phase I prototype has been replaced with a modular robotic head from TRACLabs. The Biclops 

was developed under a separate SBIR program and was originally designed for computer vision 

applications intended to incorporate two cameras for stereo vision. With full pan-and-tilt 

capabilities, this was an ideal choice for moving forward quickly on this project. 

3.1 Hardware 

The TRACLabs Biclops robotic camera-positioning mechanism is a multi-axis motion control 

platform for aiming single or multiple cameras. It is compact and lightweight, consumes little 

power, and provides excellent position observation. The pan-and-tilt axes move the camera(s) 

much like a standard camera tripod. All axes are under closed loop computer control, with 

motion commanded through a standard RS232 port. The Biclops pan/tilt (PT) mechanism is 

capable of handling as much as 2 kg at peak speeds exceeding 120°/second while drawing less 

than 20 watts of power for the motors and the controller. The controller, mounted in the base of 

Biclops, consists of an embedded servo-motor controller and brushed servo-amplifiers. The 

command interface to the controller is a straightforward packet protocol operated over a standard 

RS232 port. When a command packet, consisting of a command byte and command data is sent, 

it is immediately acknowledged by a status packet. Each axis can be polled independently for 

position and motion parameters as well as quality of performance indications (e.g., ability of axis 

to maintain commanded position). 

The pan-and-tilt motions are controlled through a C++ software interface that ATI has obtained 

from the manufacturer. Connected through an RS-232 communication port, the commanded 

position and motion are a function of user-supplied velocity profiles and feedback controller 

 5

Visual C++® is a registered trademark of Microsoft. 
8 

parameters. The feedback controller parameters essentially determine the position response 

of the system. The velocity profile for each axis consists of the velocity, acceleration and 

deceleration parameter values that set hardware performance limits on the velocity and 

acceleration for the respective motors. They are independent of the feedback controller 

parameters that govern the response time. If the controller parameters require motion in excess 

of the velocity profiles, those limits will control the motion. For the head-tracking application, 

no obvious velocity or acceleration limitation is induced by the load. Therefore, the velocity 

profiles were set at high enough values so that the feedback-controlled motion is not limited by 

those profiles. 

The wires connecting the controller board to the motor and encoder are part of a six-wire ribbon 

cable. As the axis moves at full speed, it appears to induce noise on the encoder power and 

ground lines, causing spurious spikes on one or both of the encoder quadrature output. The 

control chip interpreted this as a position command, losing count of its actual position, resulting 

in position errors of 15° to 20° when commanded independently from errors encountered in the 

head-tracking hardware. The manufacturer, TRACLabs, corrected this problem by isolating the 

wires that connect to the motor from the encoder cable lines. ATI checked the operation of the 

robotic head by operating it at high speeds over extended periods of time and found no position 

errors after the redesign. 

3.2 Software 

A demonstration program developed by TRACLabs for the Biclops robotic head served as a 

guide in our understanding and designing the software for the prototype. A demonstration 

program for the Biclops robotic head contains elements needed for this application. This 

program performs an initialization of the robotic head by determining the hard limits on the panand-tilt axis and then sets itself in the (0,0) position determined on the basis of the hard limits. 

The program then performs an uncoordinated move, in which one of the axes reaches the 

commanded position before the second one can, and a coordinated move in which both the axes 

reach their commanded positions at the same instant. The essential set-up procedures and 

functions to perform the uncoordinated axis move were identified. 

In the new application that was created for the 3D Bird, additional code to command and control 

the Biclops was added. This portion of the software establishes communication to the Biclops 

through COM Port 1, moves the Biclops head to the position entered by the user, and reads the 

position of the Biclops and displays it in an edit box. The values that the user could type to 

command the Biclops to move were restricted to ±165° on the pan axis and ±55° on the tilt axis 

to prevent the head from hitting the hard limits. 
9 

4. Command and Control Software Interface 

The command and control interface that was initially developed and used to demonstrate the 

system to ARL is shown in figure 3. 

Figure 3. First generation GUI developed for the system by ATI. 

This interface required the user/operator to be familiar with the sequence of steps to operate both 

the head tracker and the robotic head. Although this application provides the user with slightly 

more flexibility, it also requires the proper sequence of steps to be followed to properly configure 

the hardware. It was therefore determined that a more user-friendly application should be 

created that would require a minimum of interaction from the user to ensure that proper 

calibration and system setup were achieved. Therefore, the user interface was made much 

simpler and more user friendly with fewer buttons and controls and is shown in figure 4. 

All the functionalities in the first GUI were included in the final design. When the hardware 

components have been connected to the COM ports and the application loads, the first step is to 

set up the communication between the host PC and the hardware i.e., 3D Bird and Biclops. 

When the “setup/init” button is clicked, the program connects the PC to the 3D Bird through 

COM port 2 and then to the Biclops through COM port 1. If the connection to the 3D Bird fails, 

either because the device is not connected to the correct COM port or because the power supply 

is not connected, an error message is displayed in the message box and the program quits 

execution. The program will not connect the Biclops unless the 3D Bird has been connected. 

Once the communication with the Biclops is set up, the program reconnects to the Biclops at a 

higher data rate (115.2 kbaud) and then performs the homing procedure. When the homing 
10 

sequence executes, the user interface is locked and does not allow the operator to use the 

interface. This prevents the user from performing other operations before homing is complete. 

When homing is complete and the 3D Bird is streaming data, the “Ready to rock” message is 

displayed in the message window. At this point, the system is ready for use. 

Figure 4. Simplified GUI design for the final system. 

The next step is to click the “start stream” button to stream the data from the head tracker to the 

robotic head. The Biclops moves to its (0,0) position and a message window appears and 

instructs the user to look in the same general direction as that of the Biclops and level and then 

hit the “OK” button. The head tracker then resets its origin to its current physical orientation and 

begins streaming position command data to the robotic head. This manual process of coordinating remote and local orientations ensures that both heads are facing the same absolute 

direction during operation. The data streamed from the 3D Bird are checked for the allowable 

range in the pan-and-tilt axis and passed as a position command to the Biclops. The azimuth and 

elevation values are displayed in real time. The “stop stream” button disconnects the head 

tracker from the robotic head but does not disconnect the communication between the PC and the 

hardware. The “quit” button disconnects the head tracker and the robotic head and then closes 

the application. In addition to the simplifications that were made in the GUI, a context-sensitive 

“help” button was provided to assist the user in using the software. The help button returns to 

the user information based on the state of the program. Further information about the operation 

of the system is provided in Appendix A in the form of an operation manual. 
11 

5. Audio Path 

The audio path begins with the EAR. Mounted on the armature module, the EAR uses two 

relatively inexpensive microphones and two artificial pinnae for acoustic shading. The remote 

microphones are positioned at the surface of the entrance to the artificial ear canals to avoid any 

acoustic filtering that could be caused by artificial ear canals. Instead, the user’s actual ear 

canals are used to provide this acoustic filtering. The microphone signals are delivered to the 

digital signal processor after being appropriately amplified and filtered. The audio signals, after 

being processed by the DSP, are again conditioned and delivered to the stereo headphone 

amplifier. Finally, the headphones provide the audio signals to the user’s ears at the same 

magnitude and sound pressure level (SPL) as if they were heard in the actual environment. 

figure 5 depicts this entire signal path. 

Mic. 

Amp. Microphone AAF, A/D

Processing

SF, 

Headphone 

Amp.

Headphone Soldier 

Pinna

Remote 

Pinna

Soldier’s Ear 

Canal Sound

Figure 5. Audio signal path. 

5.1 Input and Output Scaling 

Each element of the audio system contains components that required unique design considerations. The 16-bit analog to digital (A/D) converter and 12-bit digital to analog (D/A) converter 

used in the customized frequency response routine must be used to their full range to maximize 

the audible dynamic range. The input dynamic range can be 90 dB, while the output dynamic 

range can only be 66 dB. Therefore, depending on the desired range of SPLs to be detected and 

heard, input and output hardware gains must be set, as well as internal DSP scaling. An example 

is presented next to illustrate these points. 

Consider a desired input range of 30 dB SPL to 120 dB SPL and a desired output range of 34 dB 

SPL to 100 dB SPL. With a calibration tone at 94 dB and a maximum input SPL of 120 dB, we 

can determine that the input voltage level should be 0.5 V to maximize the dynamic range for a 

maximum input level of 10 V peak (Vpk). Likewise, if we have a desired maximum output SPL 

of 100 dB, we need an output voltage level of 5.0 V for 94 dB SPL. This will correspond to a 

scaling through the DSP of 10. These voltage levels only ensure that the dynamic range of the 

A/D and D/A converters are optimally used. However, input and output hardware gains must be 

separately set, based on the sensitivity of the microphone and headphone speakers so that when 

presented with a 94-dB tone, the input voltage level is correct and the output SPL at the user’s 
12 

ear is correct. It should be clear that when the desired input and output SPL ranges are changed, 

the hardware gains must also be changed in order to avoid the dynamic range limitations of the 

A/D and D/A converters, which could ultimately create noise in the audio system. 

The generic audio equalization that is implemented via the Analog Devices DSP evaluation kit 

had still different input and output range requirements. The A/D input maximum is set to 3.1 Vpk

and the output maximum is 1.1 Vpk. Each input and output is 16-bit and is capable of sampling 

at 44 kHz. The input-to-output scaling is performed automatically by the EZ-kit and does not 

require separate adjustment between the input and output, since their dynamic ranges are equal. 

A 94-dB tone presented to the A/D at 0.327 Vpk provides a dynamic (SPL) range of 20 dB SPL 

to 110 dB SPL. As discussed before, the output must be scaled differently to accommodate the 

sensitivity of the headphone speakers when a 94-dB SPL tone is delivered to the actual ear canal. 

5.2 Headphone Wiring 

An interesting phenomenon was discovered when ATI tested Sony’s MDR-V900 headphone that 

was chosen for the Phase I prototype demonstration. This headphone was chosen on the basis of 

excellent reviews and specifications that indicate that the sound quality provided by this 

headphone was exceptional. Although the headphones are comfortable and the drivers are full 

range and very sensitive, it was determined through qualitative and quantitative testing that 

significant cross talk between the left and right channels existed. This cross talk was found to be 

at a signal-to-noise ratio (SNR) of approximately -30 dBa very audible left-to-right difference. 

In fact, the headphone amplifier-integrated circuit selected for this prototype indicates and 

performs at a cross talk SNR of -70 dB. 

Upon further investigation and analysis, it was determined that the source of the cross talk in the 

Sony headphones was attributable to the wiring of the headphones to the input audio jack. A 

three-wire cable is used to connect the three terminal 1/8-inch male stereo plug to the left speaker 

input, right speaker input, and ground line. A common ground line is connected to both 

speakers. The wire used in this cable is a Litz type wire approximately 6 feet long with a 

resistive impedance of approximately 1 ohm (Ω). Each speaker has a resistive impedance of 

approximately 27 Ω. Using the same ground line for both speakers generates a common mode 

resistance, which induces voltage in (for example) the left speaker when the right speaker is 

driven. The voltage divider of 1/28 corresponds approximately to the -30-dB SNR quantitatively 

determined in laboratory measurements. This problem was easily and very effectively solved by 

the use of a separate ground line for each speaker, which eliminated any significant common 

mode resistance present between the two speakers. 

5.3 Headphone Audio Path Equalization 

Figure 5 illustrates the components of the audio path from the remote microphones to the 

listener’s ear location. At the remote location, the microphone has been placed at the surface of 
13 

the entrance to the artificial pinna. Acoustically, the signal is colored by the shape of the 

external pinna but not by any artificial ear canals. It is thought that specific curvatures and 

shapes of individual pinnae contribute to localization abilities. In addition, ear canals filter the 

acoustic signals in a way that is unique to individual listeners. By only attempting to replicate 

the external features of the human ear, models are more easily created for different individuals. 

The features of ear canals extend all the way to the user’s eardrums and would be difficult to 

replicate at the remote location and to eliminate at the user’s location. This argument forms the 

reasoning behind the use of only the external ear features at the remote location. 

The audio path begins with the EAR. Mounted on the armature module, the EAR uses two 

relatively inexpensive microphones and two artificial pinnae for acoustic shading, as well as an 

artificial head form for the same purpose. The remote microphones are positioned at the surface 

of the entrance to the artificial ear canals to avoid any acoustic filtering that could be caused by 

artificial ear canals. Instead, the user’s actual ear canals are used to provide this acoustic 

filtering. A mechanism for determining listener equalization where local ear canal dynamics are 

not included was developed. Disposable earplugs combined with an identification microphone 

have been designed to fit into any user’s ear to match the location of the remote microphone in 

the external ear canal location. This permits the user’s actual ear canal dynamics to be included 

in the overall psycho-acoustic response, while the artificial pinna shapes the external ear 

response. The artificial ear microphone and identification microphone are shown in comparison 

in figure 6. 

Figure 6. Sensing microphone in the artificial ear 

(left) and identification micro-phone in 

the human ear (right). 

Although several of the components presented in figure 5 do not have substantial effect on the 

magnitude response of the system, several do. Therefore, this system is identified and equalized 

with an adaptive equalization routine. Because the magnitude response must be inverted by the 

equalization filter, a unique solution to an inversion of a causal, non-minimum phase system 

requires an acausal filter design. In practice, this is an impossible request. Since absolute phase 

shifts cannot be detected by human hearing, a phase delay was introduced into the equalization 
14 

filter path to account for the non-minimum phase portion of the audio path. This allows the 

design of a causal filter to be realizable for the minimum phase portion of the audio path that can 

be inverted. The resulting system is a flat magnitude audio path, with some additional phase 

delay to compensate for the non-minimum phase dynamics during identification. 

The audio path inversion is customizable to every individual by the implementation of an 

adaptive equalization routine. A simplified block diagram of that routine is shown in figure 7. 

Gmin + Delay W 

Delay 

Noise Input Error 

Figure 7. Equalization routine. 

A delay is applied to the input signal to account for the non-minimum phase dynamics, and the 

adaptive filter is revised, based on reducing the mean squared error between its output and the 

actual system output measured by the microphone in the user’s ear. Figure 8 illustrates the audio 

path before and after equalization for one individual. 

Figure 9 illustrates the effect of the equalization filter applied to the system of figure 7, which is 

a combination of the converged adaptive filter and the phase delay applied to the equalization 

routine. This additional phase is required in both the identification and filtering stages because 

the vector addition of the plant signal and the filtered signal must result in proper phase 

alignment for the magnitude to become 0 dB. 

Currently, the identification routine permits saving individual characteristics in MATLAB6-based 

.mat files for reloading into the DSP routine or analyzing in MATLAB at a later time. 

Customized characteristics require additional hardware and complexity as well as training. To 

reduce cost and complexity, another option was developed to identify a population of individuals 

and fit an average equalization filter to the population for use in a fixed filter system. Building a 

single fixed (analog or digital) filter for equalization is significantly less complex and may have 

acceptable (although not perfect) results. 

Figure 10 presents a small group of individual transfer functions while figure 11 illustrates the 

equalized result of the average identification. Although these results are not as perfect as those 

shown in figure 8, they may represent an acceptable and low cost solution for the initial form of 

this product. 

 6

MATLAB®

is a registered trademark of The MathWorks. 
15 

0 2000 4000 6000 8000 10000 12000

-30

-20

-10

0

10

Mag

0 2000 4000 6000 8000 10000 12000

-3000

-2000

-1000

0

1000

Phase

Freq

Figure 8. Frequency response before (lower curve) and after equalization (upper curve). 

0 2000 4000 6000 8000 10000 12000 14000

-10

0

10

20

30

Mag

0 2000 4000 6000 8000 10000 12000 14000

-200

-150

-100

-50

0

50

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Freq

Figure 9. Equalizer filter for figure 7 system. Magnitude Magnitude Phase Phase
16 

0 2000 4000 6000 8000 10000 12000 14000

-25

-20

-15

-10

-5

0

5

10

15

Freq.

Mag

Figure 10. Small population of frequency responses. 

0 2000 4000 6000 8000 10000 12000 14000

-25

-20

-15

-10

-5

0

5

10

15

Freq.

Mag

Figure 11. Population of frequency responses from figure 10, equalized with their 

average inverse. 

The two figures represent the average equalization of a population used to illustrate this general 

concept to ARL. The actual implementation of the final generic filter came from another 

population sample that was collected through the Analog Devices’ EZ-kit system that was 

ultimately delivered to ARL. The microphone amplifiers embedded in the EZ-kit imparted a Magnitude Magnitude
17 

magnitude shaping not present in the dSpace7population average. Therefore, the frequency 

responses were collected separately and a new generic filter was designed. Figure 12 illustrates 

the new population frequency responses. 

Figure 12. Population of frequency responses through EZ-kit device.

The average frequency response function (FRF) of figure 12 was created and an inverse filter 

was designed. This design was made with a cosine expansion, frequency sampling technique 

that generates a magnitude response as prescribed. The resulting filter design and the equalized 

FRFs are shown in figures 13 and 14, respectively. 

Figure 13. Equalization filter for generic solution. 

 7

See appendix A, section A-2.4. 

0 0.5 1 1.5 2 2.5 3

x 104

−120

−100

−80

−60

−40

−20

0

20

Freq.

Mag

0 0.5 1 1.5 2 2.5

x 104

−20

−10

0

10

20

30

40

Freq. (Hz)

dB
18 

Figure 14. Generic equalized frequency responses. 

6. Final System Design and Configuration 

A completely customized GUI C++ software program was built by ATI to integrate the headtracking information collected from one PC serial port with the command requirements of the 

remote robotic head via another serial port. Operating in real time, the remote robotic head moves 

simultaneously with the user’s head. Several versions of this control program were designed and 

tested, offering the user various levels of interaction with the hardware devices. The final 

program incorporates an informative help section that guides the user through trouble-shooting 

and operation of the system. The front end interface of that program is shown in figure 15. 

Figure 15. Command and control user interface. 

0 0.5 1 1.5 2 2.5 3

x 104

−40

−30

−20

−10

0

10

20

Freq.

Mag
19 

Somewhat self explanatory, the user sets up the hardware by selecting the “setup init” button. A 

message window always displays the status of the program. In addition, the elevation and azimuth 

are displayed in real time once the “start stream” button is selected. Calibration of the remote and 

local heads is also performed immediately after the command to start stream. The help button can 

be selected at any time to receive troubleshooting instructions. 

Operating on the same PC is the audio conditioning software previously discussed. Because 

real-time processing is required by the audio path, a digital signal processor is employed. A GUI 

was also designed by ATI to control, select, and customize the frequency response and filter the 

incoming signals with that response. The GUI that was designed for the audio interface is shown 

in figure 16. 

Figure 16. Audio path user interface. 

Figure 17 shows a digital photograph of the Phase I prototype system in operation, that was 

delivered to ARL. 

Figure 17. Fully functional wired binaural microphone system. 
20 

The final remote system employs a head form that is mounted on the robotic EAR to provide 

acoustic shading necessary for accurate sound field measurement. A 50-foot signal and audio 

path was employed to allow robotic deployment from the local environment, and a fixture was 

designed to permit mounting on a standard camera tripod. Additional information and 

documentation for the operation of the system is included as an operations manual in appendix A 

of this report. 

7. Conclusions 

The primary significance of the innovations proposed in the Phase I project was the productoriented design strategy, with the ultimate goal of realizing a manufacturable product at the 

conclusion of Phase II. By completing the proof-of-concept prototype during the Phase I effort 

and delivering it to the Army for further testing, ATI has virtually eliminated any technical risk 

of this proposed Phase II effort. 

The basic problem to be solved by the Phase I effort was to allow a remotely located soldier to 

monitor a potentially hostile acoustic environment with localization accuracy equivalent to 

actually being placed in that environment. The challenges for the entire program (Phase I and 

Phase II) effort are to 

• Employ state-of-the-art components so that remote hearing is equivalent to local hearing 

and may be enhanced to provide increased hearing acuity. 

• Provide wireless data and audio transfer between the local and remote listening locations. 

• Employ a design approach that combines the latest in technology for each component but 

minimizes the cost/performance ratio. 

• Focus on a product-oriented design so that the end result is a robust, fieldable, 

manufacturable system rather than a research-based bench-top prototype. 

The successful completion of the proposed Phase I effort was marked by a proof-of-concept 

prototype employing primarily COTS components. The Phase I prototype employed features 

and functionality that defined the effectiveness of the design in an actual remote acoustic 

environment. The Phase I option will add the remaining features envisioned for the fully 

functional product at the completion of Phase II. During the Phase II effort, ATI will establish 

original equipment manufacturer (OEM) relationships with component manufacturers to develop 

customized designs specific for the wireless binaural microphone. The most challenging 

anticipated research element of Phase II will be the inclusion of the wireless data communication 

between the remote location and the local listening location. The successful conclusion of the 
21 

Phase II effort will be marked by a wireless binaural microphone system ready for production, 

which was developed by ATI with the support of specific OEMs. 

Phase I has shown that the technologies to facilitate the successful construction of a real-time 

audio telepresence device for remote acoustic monitoring are commercially available, cost 

effective, and technically sound. ATI has employed a design and construction strategy that 

ensures a fully manufacturable prototype will result from the Phase II effort. The successful 

completion of all Phase I technical objectives has guaranteed a successful conclusion to the 

Phase II program. 
22 

INTENTIONALLY LEFT BLANK 
23 

Appendix A. Wired Binaural Microphone: User and Instruction Manual 

A-1. Introduction

The ATI wired binaural microphone prototype is a real-time audio telepresence device for 

remote acoustic monitoring. The Phase I “alpha” prototype delivered here consists of several 

commercially available components including the Ascension Technologies’ 3D Bird used for 

head tracking and TRACLabs’ Biclops robotic head used for remote head and ear motion. 

Delivered with this prototype are two equalization systems for the electro-acoustic signal path. 

One system is based on Analog Devices DSP evaluation kit. This system is non-customizable by 

the user. A population equalization was averaged and designed to run in real time on the 

evaluation kit. The second option is being offered to ARL for a period of approximately 4 weeks 

since it uses hardware and software currently owned by ATI. This system permits usercustomizable frequency response at a slightly lower sampling rate than the non-customized 

solution. 

The following paragraphs provide a brief overview of the hardware characteristics of the system 

components. Although it is advised that the user read this entire manual, Section 2.0 is not 

necessary if the user wishes to begin using the device immediately. 

A-2. Hardware Overview 

A-2.1 3D Bird 

The 3D Bird is a device that measures the orientation of a small sensor in real time, allowing 

orientation (angular) tracking of any object to which it is attached. The 3D Bird determines 

orientation by measuring output from solid state inertial and non-inertial sensors. Since no 

signal transmitter is needed to perform measurements, the motion area of the 3D Bird is virtually 

unlimited. The tracker consists of a small sensor unit (sensor) that is attached to the headphones 

and connected to the COM port of a PC through an RS-232 cable. No intermediate electronic 

unit, which simplifies the system setup, is needed. The sensor unit includes all the sensors as 

well as the microprocessor that controls sensor data acquisition and communication between the 

3D Bird and the host computer. 
24 

Figure A-1. 3D bird attached to headphones. 

Specifications 

Technical 

Degrees of Freedom: 3 (Orientation) 

Angular range: All altitude (±180°yaw, ±90°pitch, ±180°roll) 

Angular Accuracy: Static Accuracy 2.5° root mean square (rms) 

Dynamic Accuracy: 4.0° rms 

Angular Resolution: 0.2° 

Refresh Rate: As many as 160 measurements/second 

Maximum No. of Sensors: 1 per serial port 

Maximum Angular Speed: 1000°/second 

Computer Interface: Connects to RS-232 port of host computer 

Dynamic Lag: 15 milliseconds at 360°/second 

Physical 

Sensor Size (L x W x H): 1.41 inch x 1.08 inch x 0.92 inch 

Sensor Weight: 1.0 oz. 

Sensor Cable: 15 feet 

Electrical 

Power: 5 volts direct current (VDC) @ 100 mA 

Environment 

All specifications are valid at 30°C ±10° in an environment void of large metal objects 

and electromagnetic frequencies other than the power line. 

3D Bird Product Advisory 

The 3D Bird sensors, along with their attached cables/connectors, are sensitive electronic 

components. Most failures in the field occur because the cable attached to the sensors is 

mishandled. Always remember that these components are not designed to withstand 
25 

severe jolting, contortions, or high impact shocks. When handling the cables, please 

observe the following: 

• Never flex, pull, or twist cables. This is the most common cause of tracker failure. Note 

that there is a strain relief where the sensor head attaches to its cable. Its job is to protect 

the delicate connection between the cable conductors and the sensor assembly head. It is 

also the area in which sensors are attached to the object that is being tracked. Be sure 

you do not pull, twist, or repeatedly bend the cable. 

• Never yank the sensor off its mounting bracket or holder by grabbing the cable and 

pulling. 

• Never carry, throw, or swing a sensor by its cable. 

• Never let the sensor impact with a hard object. 

• Never add your own extensions/connectors to the sensor/transmitter cables. These 

cables are precisely bundled and shielded to minimize noise and ensure accurate 

performance within specification. If you add an extension, you may compromise the 

performance and/or negate certain regulatory certifications. 

WARM-UP PERIOD 

A minimum warm-up period of 15 minutes is required to allow electronic circuitry time 

to equilibrate to temperature changes in order to achieve the highest degree of accuracy 

from the tracker. 

A-2.2 Biclops 

The TRACLabs Biclops robotic camera positioning mechanism is a multi-axis motion control 

platform. It is both compact and lightweight, consumes little power, and provides excellent 

position observation. All axes are under closed loop computer control, with motion commanded 

through a standard RS232 port. The Biclops PT mechanism is capable of handling as much as 

2 kg and peak speeds exceed 120°/sec while drawing less than 20 watts of power for the motors 

and the controller. The controller, mounted in the base of Biclops, consists of an embedded 

servo-motor controller and brushed servo-amplifiers. The command interface to the controller is 

a straightforward packet protocol operated over a standard RS232 port. When a command 

packet, consisting of a command byte and command data, is sent, it is immediately 

acknowledged by an operating status packet. Each axis can be polled independently for position 

and motion parameters as well as quality of performance indications (e.g., ability of axis to 

maintain commanded position). 
26 

Figure A-2. Remote acoustic sensor shown with 

head form and ballast weights on 

biclops and tripod mount. 

Specifications 

Mass (without head form and weights): 1.1 Kg 

Overall dimensions (without head form): 155 mm (H) x 160 mm (W) x 101 mm (D) 

Mounting hole pattern: Four threaded holes (6 mm deep) 53 mm x 53 mm square pattern 

Power consumption: 24 V motor power 500 mA 

Pan Tilt 

Range of motion ±170° ±60° 

Maximum speed 120°/sec 120°/sec 

Maximum acceleration 300°/sec2 300°/sec2

Resolution 1.8 arc-min 1.8 arc-min

(encoder ratio) (33.33 counts/deg.) (33.33 counts/deg.) 
27 

Biclops Product Advisory 

•Never flex, pull, or yank the power cable or the serial cable.

• Switch the DC supply off when trying to move/place the head form. If the supply is 

on and the PT axis is stalled by hand, the motor could burn. 

•Fix the robotic head to a base while in operation. An adapter has been designed to 

connect with a standard tripod mount. 

A-2.3 EZ-Kit Analog Devices DSP 

The portable DSP evaluation kit is used here to condition the remote acoustic sensor signals 

before being delivered to the user’s ears. Specifically, a population average of frequency 

responses from the input microphone to a real-ear microphone was collected. The magnitude of 

this average was inverted to effectively equalize the electronic and artificial acoustic path from 

the remote microphone to the user’s ear canal entrance. This filter was implemented with a finite 

impulse response filter structure with 56 weights, at a sampling frequency of 44 kHz. 

Figure A-3. EZ-kit DSP evaluation board for generic population equalization. 

Specifications 

Technical 

Two 16-bit A/D and D/A channels for stereo audio via 1/8-inch stereo jacks 

User-programmable sample rate and input/output filter cutoff frequencies 

User-swappable electrically erasable programmable read-only memory (EEPROM) 

User programmable only with specified software (not provided) 

Electrical 

Power: 9 VDC @ 1200 mA 

EZ-Kit Product Advisory 

Handle the circuit board carefully, observing safe handling practices for electrostatic 

shocks. There are no serviceable parts on the board. 
28 

A-2.4 PC-Based dSpace DSP System 

The dSpace system is a PC-based industry standard architecture (ISA) card coupled to an analog 

interface box, and user-controllable and programmable via the PC. C-code is written to run in 

real time on the DSP. The host computer provides control over global variables in the real-time 

code via a program called “Cockpit”. This is a graphical environment that has already been 

designed for the wired binaural microphone (WBM) interface requirements. This system can be 

used to determine unique frequency response characteristics of specific individuals, having those 

responses applied to the WBM in real time, or they can be saved for later usage. Because this 

more complex solution was developed and implemented with hardware owned by ATI, it will 

only be made available to the Army for a short period of time following system delivery. This 

will permit ARL to analyze the utility of a customized FRF versus a more generic equalization 

on the EZ-kit system described. 

Figure A-4. Dspace analog interface box and PC. 

Specifications 

Technical 

Two 16-bit A/D and two 12-bit A/D channels, all ±10V input range 

Four 12-bit D/A output channels, all ±10V input range 

User-programmable sample rate with internal timer 

User controllable via software interface “cockpit” 

Texas Instruments C31 DSP processor 

PC-based system 

dSpace Product Advisory

• There are no serviceable parts inside the computer, so please do not open it. 

• The C-code has been written specifically for the performance of this project and 

should not be altered in any way. 
29 

• The GUI has been designed specifically for the performance of this project and 

should not be altered by the user. 

A-2.5 Analog Interface and Signal Conditioning 

One final required element of the design is a “breadboard” containing signal conditioning for the 

microphones (when used with the dSpace controller) and a headphone amplifier when used with 

either of the two equalization options. Because of the varying dynamic ranges between the two 

systems, the input attenuator must be changed via a voltage divider resistor network when one is 

switching between the two equalization systems. The microphone amplifiers and filters are 

already built into the EZ-kit circuit board but are required as external components for the dSpace 

system to properly condition the input and output. Instructions for switching between the two 

systems are included in the following sections. 

Figure A-5. Analog interface circuitry. 

Specifications 

Technical 

Two-channel audio power amplifier for headphones with input and output 1/8-inch stereo 

jacks 

Three-input/three-output amplified anti-alias filters at 10.5 kHz for microphone signal 

conditioning (left microphone, right microphone, and ID microphone) each employing 

three poles 

Two-input/two-output smoothing filters at 10.5 kHz for DSP output, three poles each 

A-2.6 List of Delivered Hardware 

Hardware That ARL May Keep 

• One sensor unit (3D Bird head-tracking system) mounted on a Sony head set with 

RS232/power cable attached 

• One 100 to 240 V alternating current (AC), 1.0 A, 47- to 63-Hz regulated power 

supply with power cord for the 3D Bird 
30 

• One robotic head unit (Biclops) fitted with a head form, ballast weights, artificial 

ears, and microphones 

• One 100 to 240 V AC ~50- to 60-Hz input, 24 V 1.5 A switching power supply for 

Biclops. 

• One 50-foot serial cable (RS 232 cable for the Biclops) 

• One microphone extension cable 

• One EZ-kit DSP evaluation board with associate power supply (9V 1200 mA) 

equipped with pre-programmed EEPROM for generic equalization 

• One stereo 1/8-inch male to 1/8-inch male connector cord 

• One breadboard and power supply model number PP272 with headphone amplifier 

circuit and audio interface panel 

• This user manual 

• One CD containing command and control software and documentation 

• Warranty information for the 3D Bird and Biclops 

Hardware That ARL Must Return to ATI After 4 weeks 

• Slimline PC and 17-inch monitor with mouse and keyboard containing dSpace ISA 

card, and associated software for customized audio path 

• Connector panel for dSpace system 

• Filter and amplifier semiconductors and hardware mounted on PP272 board (not 

including headphone amplifier) 

• Associated cables and connectors that couple the dSpace connector panel with the 

filter modules on the PP272 

Hardware That ARL Will Require After 4 Weeks 

• A PC with two available COM ports 

A-3 System Installation 

A-3.1 3D Bird Hardware Installation 

The sensor should not be situated near power cords, power supplies, or other low frequency 

current-generating devices. Their emanations will be detected by the sensor and converted into 

noise on the output orientation measurements. The sensor will detect noise when it is operated 

near a CRT-type display. The amount of noise will vary, depending on the operating frequency 

of the CRT and the amount of shielding built into the CRT. 

To connect the 3D Bird to your computer, you need to do the following: 

• The host PC can be switched ON/OFF. 

• Attach the serial end of the 3D Bird RS232 power cable to serial port COM2 of your 

computer. Screw in this connector. 

• Plug the power supply into the electric outlet. 

• Power can then be turned on and commands sent to the 3D Bird. 
31 

A-3.2 Biclops Hardware Installation 

To connect the Biclops to your computer, you need to do the following: 

• The host PC can be switched ON/OFF. 

• Attach the 50-foot serial cable securely to the serial interface port on the robotic head 

and to COM1 of the PC and screw in the connectors 

• Plug in the supply for the Biclops and turn on the power on the Biclops via the small 

switch next to the power cord (the green light should be on) 

A-3.3 Command and Control Software Installation 

The package comes with a compact disc with the necessary software to run the application. The 

disc consists of the following files: 

• WiredBinauralMic.exe 

• 3DbAlg.dll 

• 3DBird.dll 

• Mfc42d.dll 

• Mfc042d.dll 

• Msvcrtd.dll 

Create a working directory of your choice. Copy all these files into your working directory. 

Double click the WiredBinauralMic.exe file to start the application. The interface shown in 

figure A-6 should appear. 

Figure A-6. Command and control graphical interface. 

To test the hardware and software installation, click the “setup init” button and view the message 

screen and the Biclops. The Biclops will begin to move to identify its center position. If all 
32 

devices are set up correctly, when the Biclops completes homing, the message “ready to rock” 

will appear in the message window. If this message does not appear, refer to the “troubleshooting” section to identify potential problems or use the “help” feature on the GUI. 

A-3.4 Generic Audio Path Hardware Installation 

The generic audio path consists primarily of the EZ-kit and audio amplifier on the PP272 circuit 

board. The input resistor network must be modified from the dSpace settings to ensure proper 

calibrated SPL at the ear location. An input voltage divider is used to adjust the level coming 

from the D/A. Follow these steps to connect the system: 

• Ensure that the input voltage divider on both the left and right inputs has a 5.6-kΩ

resistor input and a 3.9-kΩ resistor to ground. Check with ATI if any confusion exists 

about how to accomplish this. 

• Connect the 1/8-inch stereo microphone plug that is coming from the Biclops head 

system to the “input” stereo jack of the EZ-kit. 

• Connect one end of the 1/8-inch male, 1/8-inch male extension cord to the “output” jack 

on the EZ-kit. Connect the other end of this cord to the input jack of the stereo 

headphone amplifier on the breadboard. 

• Connect the headphones to the output jack of the stereo amplifier on the breadboard. 

• Ensure that power is connected to both the EZ-kit with the supplied DC power supply 

and to the breadboard with a standard power cable. 

• Switch both microphones on at the in-line pre-amplifiers near the Biclops. 

You should now hear the microphone signals at normal SPL levels; you can test this by rubbing 

your fingers or snapping near the remote ears. 

A-3.5 (temporary delivery) Customized Audio Path Hardware Installation 

All the required software and hardware on the PC have been pre-installed upon delivery. The 

operating instructions for that software and hardware are given in the following section. 

The dSpace system is not equipped with anti-alias or smoothing filters, necessary for accurate 

digital signal reconstruction. These filters were built by ATI on the same circuit board that holds 

the audio power amplifier. The proper connections between the dSpace connector panel and 

filter hardware must be made. The microphone signal from the Biclops is connected to the 

WBM input, and its output is connected to channels 1 and 2 of the dSpace connector panel. The 

identification microphone is connected to the middle (mono) microphone input on the circuit 

board, and its output is connected to channel 3 of the dSpace connector panel. Finally, outputs 1 

and 2 of the dSpace connector panel are connected to the smoothing filter (stereo) input, and its 

output is connected to the input of the stereo headphone amplifier on the other side of the circuit 

board. The headphones are then connected to the output of the stereo headphone amplifier as in 

section 3.4. 
33 

The headphone amplifier for the dSpace customized audio path system requires a different 

voltage divider for the input to the stereo headphone amplifier. Ensure that this divider is in 

place for both left and right signal paths before operating the audio path. The appropriate 

voltage divider for the dSpace system consists of an input resistor of 5.6 kΩ and a 68-Ω resistor 

to ground. 

A-3.6 (temporary delivery) Auto-Run Batch File and Custom Audio Path Equalization 

Software 

ATI has combined ALL start-up requirements for the customized audio path into a single batch 

file that is situated in the center of the desktop titled “wired binaural microphone”. Simply 

double click this icon, and several programs will be launched. First, ControlDesk will establish a 

host connection with the DSP, the audio code will be complied and downloaded to the DSP, 

cockpit will launch, MATLAB will launch, and finally, the C2 GUI for the robotic head and 

head-tracking hardware will be launched. 

Once all windows are open, it is safe to close ControlDesk and minimize or close MATLAB, 

depending on desired usage. Click the “start” button on the cockpit window, and the edit mode 

will change to the animation mode shown in Figure A-7. 

Figure A-7. Customized acoustic equalization interface. 

To check the audio path, click the radio button from zero output to “echo both channels”. You 

should then hear the remote microphones, albeit unequalized. 

A-4. Operating Instructions 

The head-tracking/robotic head interface and control are handled separately from the audio path 

hardware and control. Therefore, the two systems are discussed independently to simplify 

troubleshooting and setup. Because the two systems are independent, it does not matter which 

one is set up and initialized first. Figure A-8 shows the full system during operation. 
34 

Figure A-8. Full system during operation. 

A-4.1 Head and Tracking Command and Control 

The robotic head will track the user’s movements in real time after the system has been properly 

configured. 

• Ensure that power is connected and on for both the 3D Bird and the Biclops. 

• Don the headset (with the Bird attached) and position it in a comfortable location on 

your head. Be sure that this position does not move relative to your head after it has 

been set. 

• Double click on either the shortcut application on the desktop or the Wired Binaural 

Microphone.exe application, as described in the previous section. 

• When the application loads, press the Setup/init button (see figure A-6). This will set 

up communication with the Bird and then to the Biclops. The Biclops will go through 

a homing sequence to identify the hard limits on both the pan and tilt and returns to 

its mechanical origin. During this time, the GUI prevents the user from controlling 

any aspect of the system. This robust feature ensures that the required homing 

procedure completes successfully. 

• Once homing is complete and the 3D Bird is successfully initialized, the message 

“Ready to Rock” will be seen on the message window below the “setup init” button. 

At this point, hit the “start streaming” button. A message window will appear, 

instructing the user to look in the same direction and level as the robotic head; then 

hit “OK”. This action manually establishes coherent directions of the robotic and 

human head directions and ensures that when the human looks north, the robotic head 

is also looking north. 

• Click OK while looking in the direction of the Biclops. The Bird will reset its origin 

or reference to the current orientation and start streaming (orientation) 160 data 

records per second (azimuth and elevation, at a baud rate of 38,400) to the Biclops. 

The PC then interfaces through COM1 with the Biclops at a rate of 115,200 baud and 

conveys the orientation information. The robotic head then tracks the head 

movement in real time. 
35 

• If you need to stop streaming, hit “stop stream”. This will cause the streaming from 

the head tracker to the robotic head to stop but does not disconnect the devices from 

the PC. This is essentially a pause feature that allows repeated use but does not 

require another homing procedure. 

• Note that each time the “start stream” button is pressed, the user must calibrate his 

head location with that of the 0,0 position of the Biclops. Biclops automatically 

returns to 0,0 as soon as the “start stream” button is hit and before the user is required 

to calibrate. 

• If you want to quit the application, hit “quit”. This stops the streaming and 

disconnects the two devices from the PC and closes the application window. If the 

application is restarted, the homing procedure will commence. 

An additional help feature is provided and is activated by the “help” button on the GUI. This 

feature is context sensitive and will provide instructions/help to the user, based on the current 

state of the application. If any problems are encountered during any step in the process, the help 

button can be pressed and troubleshooting assistance will appear. 

Although the hard limits for the pan-and-tilt axis for the Biclops are 170° and 60°, the implementation for the wired binaural prototype has further reduced it to 165° and 55°. This has been 

done to ensure that the Biclops does not physically hit the hard limits when the local user moves 

his head toward it. In addition, when the pan/azimuth exceeds the pre-set limit of ±165°, the 

robotic head remains at ±165°, as may be the case, until the pan orientation data being streamed 

fall back within the specified limits. Similarly, on the tilt axis, the robotic head will remain at 

±55°, as may be the case, until the tilt values fall within the allowed range. 

A-4.2 Generic Audio Path Operation 

The generic audio path has been pre-calibrated and pre-designed to generically accommodate all 

users. A population frequency response was collected and used to generate an average inversion 

filter, which was implemented on the EZ-kit device. Once power is applied, this filter is engaged 

on both left and right channels and does not require any user interaction to achieve calibrated and 

equalized audio path delivery to the user’s ears. If after installation, no audio is apparent, 

• Ensure that power is applied to the EZ-kit and the green light-emitting diodes (LEDs) are 

on. 

• Ensure that all audio signal connections are correct as defined in the previous section. 

• Ensure that power is applied to the circuit board and that all circuit connections have 

been properly made. 

• If the audio sounds too low, ensure that the proper resistor network (voltage divider) is in 

place for the generic filter operation. 

The filter cannot be changed by the user. It is possible that alternate filter designs may be used, 

but they must be pre-designed and burned onto an EEPROM at ATI. This capability is not 

provided to the end user at this time. 
36 

A-4.3 (temporary delivery) Customized Audio Path Hardware and Software Operation 

The audio path can be customized for a specific individual. This involves equalizing the 

electronic and acoustic frequency responses between the remote and local ears. This is done by 

first identifying the frequency response and then filtering the incoming signals with an inverse of 

that response. The result is a flat magnitude response between the remote and local ears, 

ensuring accurate SPL delivery at all frequencies. The 1000-Hz, 0-dB gain of the audio path has 

been pre-set, based on a calibrated tone being delivered at the remote location and set at the local 

location. While this gain is adjustable on the audio path GUI (shown in figure A-7 as “calibration scale”), it does not need to be altered by the user. 

After the application is loaded via the desktop icon, the user must press “start” in the cockpit 

window in order to control the GUI. The following steps outline the chronological operation of 

the customized audio path: 

• Place the headphones comfortably on your head. Remember that their position also 

controls the head tracker information.

• The “system state” menu items govern the operation of the audio path. The default 

setting is zero output, which does not generate any audio at the headphones.

• In order to check the operation of the device, select “echo both channels”. This sends the 

audio signals from the remote location to the local location, with calibrated signals at 

1 kHz. No frequency response equalization is performed on these signals; it simply 

echoes the input to the output with appropriate gain for calibrated 1-kHz delivery.

• “Filter both channels” will filter the input with the equalization filter designed during the 

identification process. If no filters have been designed, no sound will be heard.

• In order to design the filters, a microphone must be placed in the user’s ear that 

corresponds to the identification channel. The microphone is placed in a manner similar 

to that at the remote location (see figure A-9). 

Figure A-9. The local user places the microphone 

facing out, using the pre-fabricated earplugs 

designed for holding the microphone. 
37 

• Once the microphone is in place (for example, the right ear), the headphones are placed 

on the user’s head (ensuring that the right headphone goes to the right ear). Then the user 

selects “ID RIGHT” from the system state menu. The user will hear a white noise signal 

from the right earphone. The volume level (sound interface device noise level) is pre-set 

and should not need adjusting. The user should carefully watch the “squared error” 

level indicator. When it reaches a very low value, the identification procedure has 

converged on an acceptable solution and can be paused. If during the identification 

procedure, the headset is moved or a large SPL is received at the ear microphone, 

the routine may diverge. This will be noted by a red bar occupying the “squared 

error” indicator. In this case, pause the routine, reset the filter by pressing “reset 

right,” and repeat the identification, being careful to remain still.

• Repeat the identification procedure for the left ear by placing the identification 

microphone in the left ear and pressing “ID LEFT”. 

• Once the filters have been identified, the user can select “filter both channels” to hear the 

equalized remote microphone signals. 

• “Reset right” and “reset left” will set the filters to zero but only when the system state is 

in “zero output” mode. 

The advanced user may also have access to the filter weights themselves by accessing the table 

editors to the far right of the cockpit GUI. The table editors (not shown) allow the user to load 

and save the identification weights from the DSP and view them in a MATLAB format file. In 

addition, old weights can be reloaded by the user to avoid the identification routine described. 

• Scroll the GUI to the right to reveal the table editors for “11” or the left ear and “22” or 

the right ear. 

• For each table, “manual refresh” collects the most recent weight vector from the DSP. 

“Save” permits the user to save the vector weights in a MATLAB format .mat file. 

“Load” allows the user to load a predetermined weight vector from a .mat file to the 

cockpit buffer, and “download” sends those weights in the buffer, to the DSP. Warning: 

Only vectors originally developed in the cockpit GUI can be reloaded at a later time. 

Do not attempt to manually generate a filter for loading on the DSP; the format will 

be incorrect.

• A MATLAB m-file called convafwts.m is provided to display the frequency response of 

the filter that is saved. 

A-5 Troubleshooting 

As before, the audio and C2 systems operate independently. Therefore, the troubleshooting and 

problem solving help presented here is divided into these two system components. 

A-5.1 Command and Control Software and Hardware 

If you are experiencing trouble with the application and you get the following on-screen 

messages, try the suggested steps: 
38 

Cannot communicate with bird device: 

• Ensure that the power supply is plugged into the external power before the application 

tries to communicate to the 3D Bird (before hitting “setup/init”). 

• Ensure that the 3D Bird is plugged into the COM Port 2.

• Ensure that you do not have multiple applications trying to use COM port 2. 

Unable to read data from 3D Bird device (bad data): 

• Ensure that the 3D Bird is not placed directly on top of metal during operation. Keep the 

Bird at least 2 inches away from metal. 

• If orientation data are continuously drifting, ensure that you keep the 3D Bird still hitting 

the “OK” button in the pop-up window that instructs the user to look in the general 

direction of the Biclops. The 3D Bird performs self-calibration that takes about 

0.5 second and needs to stay still during this period of time. 

Cannot communicate with robotic head (Biclops) device: 

• Ensure that the power supply is plugged to the external power before the application tries 

to communicate to the Biclops (before hitting “setup/init”). 

• Ensure that the Biclops is hooked into COM Port 1. 

• Ensure that multiple applications are not trying to use COM port 2. 

Head tracker and robot head not connected: 

• The power supplies to the Bird and the Biclops may not be connected. 

• The Bird and the Biclops may not be connected to COM2 and COM1, respectively, or 

may not be connected at all. 

• The toggle switch for the Biclops may not be turned on. (Check for the green LED on the 

back of the Biclops.) 

The robotic head may move even when the user head does not move because of bad data from 

the head tracker. This is an anomaly of the 3D Bird device. If it becomes affected by an 

electromagnetic field, it can generate bad data, causing the Biclops to respond inappropriately. 

This is especially noticeable when the device is static. Continue moving the device, and the data 

may become more reasonable. If the data are scrolling continuously in either axis, the device 

may need to be “degaussed”. This can be done with a tape eraser available at Radio Shack8

. 

This condition typically corrects itself after several minutes. 

In case any of the above steps do not solve the problem, do not open the hardware (Biclops or 

Bird). The manufacturers’ warranties may be invalidated. There are no fuses or other userserviceable parts in the 3D Bird sensor or Biclops. 

A-5.2 Generic Audio Path Hardware 

If the audio path is not working, ensure that power is on for both the circuit board and the EZ-kit. 

Ensure that all wired connections are made and that the proper voltage divider has been put in 

place. 

 8

Radio Shack® is a registered trademark of the Tandy Corporation. 
39 

A-5.3 (temporary delivery) Customized Audio Path Hardware 

This option will be delivered completely assembled. If the audio path does not operate properly, 

consider the following items: 

• Batteries and power switches for the in-line microphones connected to the robotic head 

must be on and fully charged. 

• Connect the microphone to proper input on circuit board; output of this stage goes to 

input 1 and 2 on dSpace interface. 

• Ensure that identification microphone is plugged in, powered on, with a charged battery. 

• Ensure that identification filter has been created before selecting “filter both channels”. 

• Ensure that correct voltage divider is put in place on audio amplifier board. 
40 

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