ECHOFREE™ ACOUSTIC ECHO CANCELLER USER MANUAL
Contents
1. Power Not Required Condenser and electret microphones need phantom power Dynamic microphones do not Phantom power may damage a dynamic microphone If you are not sure whether the microphone needs phantom power check the microphone specifications If a microphone is connected to the MIC INPUT and the microphone requires phantom power set the PHANTOM POWER switch to PHANTOM If a microphone preamplifier or a microphone is connected to the MIC INPUT and nei ther device requires phantom power set the PHANTOM POWER switch to OFF Copyright 1999 All Rights Reserved CALIBRATION CALIBRATION OVERVIEW Note Important ABOUT SIGNAL LEVELS Important Important For the EF400 to work effectively you must calibrate the input and output signal lev els correctly Calibration is required to relate a loudness value as measured by a sound level meter to the electrical signal associated with the loudness The calibration procedure is required only to adjust the EF400 to accommodate the electrical characteristics of your conferencing equipment The procedure permits you to connect the widest possible variety of equipment to the EF400 The calibration pro cedure does not train the AEC The EF400 does not require training In calibration mode the EF400 generates a precise noise signal for measuring the characteristics and sensitivity of the microphone You only need to perform this cali bration at the initial installation2. on the trimpots for MIC INPUT SPEAKER OUTPUT REMOTE INPUT and REMOTE OUT PUT Refer to Figure 3 on page 10 for additional information corresponding connector To increase the level of the room or remote The markings on output trimpots refer to the level that is output on the output turn the trimpots clockwise towards 4dBu be input to the EF400 If the REMOTE INPUT signal is too low to boost the signal turn the trimpot adjuster clockwise towards 20dBu Note that both input and output trimpots must be turned clockwise to boost the input and output signals but the text around the output trimpots is in reverse order to the text around the input trimpots The markings on the input trimpots correspond to the levels expected to ASPI Digital The Sound of DSP 9 EF400 USER M ANUAL m MIC GAIN e LINE S9 MIC RECORD PLAYBACK REMOTE REMOTE SPEAKER MIC TPUT INPUT TPUT INPUT 8 8 ees gee E uds R17 amp R33 Be R25 3 R24 oe R5 2 R5 8 12 6 4 2044 4 20 20 4 447 320 SINGLE TURN POTS TURN CAREFULLY DO NOT EXCEED TURNING ARC Caution 7 USE STATIC SENSITIVE PRECAUTIONS
3. 5kHz switch is down on the 7 0kHz side the EF400 is operating in 7 0 kHz mode The switches rock up and down rather than sliding from side to side Switches through 3 are reserved Keep them in the factory default positions The factory default positions are ON 1 OFF 2 and OFF 3 A switch is off if the left side is pressed down SETTING THE BANDWIDTH SWITCH Wide Bandwidth Narrow Bandwidth Keep this switch in the 7kHz position for most applications If you use a wide bandwidth 7kHz CODEC set the bandwidth switch to the 7kHz position If you connect to wideband and narrowband connections that is if your sys tem connects to a wideband video CODEC or a narrowband telephone connection through the EF200 for different calls set the bandwidth switch to 7kHz If you connect only to narrowband terminals set the bandwidth switch to the 3 5kHz position In extreme conditions you may find that the EF400 works better in the 3 5 kHz mode SETTING THE RUN SETUP SWITCH Whenever you calibrate the EF400 set the RUN SETUP switch to SETUP position Dur ing normal operation set the RUN SETUP switch to the RUN position Setup mode is active only if the EF400 is reset when the RUN SETUP switch is in the SETUP position The EF400 may be reset by changing the bandwidth switch back and forth Setup mode is exited and normal operation restored when the RUN SETUP switch is set to RUN SETTING THE PHANTOM POWER SWITCH Power Required
4. OUTPUT and the TAPE RECORD output The EF400 continues to adapt even though its output is muted The mute signal can be provided by any normally open contact The contact can be a switch on a microphone or control panel or provided by a relay closure output on another piece of equipment til Unmuted Muted Figure 4 Schematic of mute button If the switch is open a the EF400 is not muted If the switch is closed b the REMOTE OUTPUT and TAPE RECORD are muted If you mute the EF400 externally such as with the PRIVACY feature on the EF200 the TAPE RECORD output will not be muted RECORD AND PLAYBACK If you have a tape recorder connected to the EF400 s TAPE RECORD and TAPE PLAY BACK jacks you can record conferences or play back material to parties on the both ends When you record both ends of the conversation are recorded on the tape When you play a tape the audio is sent to the remote end as well as the local end If you have a standard tape deck simply press play or record to play back audio or record a conference The figure below shows how the record and playback signals are routed Speaker Output Remote Input Microphone Input Remote Output Playback Figure 5 Record and playback signal paths ASPI Digital The Sound of DSP 17 EF400 USER M ANUAL GENERAL CONFERENCING GUIDELINES The EF400 adapts exceptionally well to changes in room acoustics but audio quality will be even better when
5. conference participants follow these guidelines 18 1 Sit or stand in one place and near a microphone Moving around the room and toward or away from the microphone while talking may cause speech audio to fade in and out Speak clearly and directly toward the microphone Keep the microphone away from noise sources such as computer fans air ducts or coffee makers Excessive noise can be annoying to people on the remote end and reduce intelligibility It can also hamper the adaptation logic and degrade EF400 performance Copyright 1999 All Rights Reserved TROUBLESHO OTING TRO UBLESHO O TING No OUTPUT TO LOUDSPEAKERS YOU CAN T HEAR THEM Check the REMOTE input level indicator If the LED bar graph meter shows activity the EF400 is receiving a signal In this case the problem is between the EF400 and the speaker If there is no activity on the REMOTE input level indicator the EF400 is not receiving a signal In this case the problem is between the EF400 and the microphone on the remote end Check the CODEC or EF200 output by connecting it directly to the amplifier or powered speaker If you hear nothing the EF400 is not causing the problem and the source of the problem is elsewhere in the system Make sure the CODEC or EF200 output is connected to the REMOTE INPUT Make sure the CODEC or EF200 is turned on and a call is established Make sure everything on the remote end is working properly Make sure the cabl
6. the speaker when in normal operating mode This alignment reduces the maximum acoustic gain allowed in your conferenc ing setup Step 4 Calibrate This step matches the remote input level to the microphone input level by matchin y g Remote Input the level on the REMOTE INPUT LEVEL INDICATOR to the level on the MICROPHONE INPUT LEVEL INDICATOR If the EF400 is connected to an EF200 Phone Add turn the REMOTE INPUT trimpot to 20 dBu fully clockwise EZ Important During this step you must be able to converse with someone at the remote end of the communications link It is also important to eliminate extraneous noise such as other people speaking at both ends of the communications link as such noise would inter fere with MICROPHONE INPUT LEVEL INDICATOR and REMOTE INPUT LEVEL INDICA TOR readings 1 Position yourself so that you can easily see the EF400 front panel signal level indicators and reach the REMOTE INPUT trimpot Now move the local room microphone so that it is facing you at a normal speaking distance usually 1 1 5 meters when you are in this position 2 Instruct the person at the remote end to sit at a normal distance from the remote microphone usually 1 1 5 meters Have this person read something to you using a normal speaking voice 3 While the person at the remote end is talking adjust the REMOTE INPUT trimpot until normal conversation level consistently illuminates the three green LEDs
7. together to mute the system e POWER SUPPLY INPUT The power supply input accepts a 5 pin DIN male connector Only use a power supply provided by ASPI Digital Se oo Power 1 ground 2 ground 3 5Vdc 4 15Vdc 5 15Vdc ASPI Digital The Sound of DSP 29 BLOCK DIAGRAM 30 EF400 USER M ANUAL Speaker Remote Output Input Remote Mic Input Output Record Playback Copyright 1999 All Rights Reserved
8. 2 n a 3 RUN SETUP 7 0 kHz 3 5 kHz OF o o PHANTOM EchoFree EF400 A quality product made in the USA 24 DIGITA DEAC fF GEF Figure 3 EF400 Circuit Board Layout Caution Do not damage the EF400 s circuitry Use the plastic static safe trimpot adjuster shipped with the unit for all adjustments Do not use a metal screwdriver or allow jewelry chains or pendants to contact the EF400 enclosure Metal tools and objects may cause a short circuit damage the circuit board and void your warranty Caution When using the supplied trimpot adjuster to adjust signal levels do not touch any other components on the EF400 circuit board with the trimpot adjuster 10 Copyright 1999 All Rights Reserved CALIBRATION CALIBRATION STEPS Step 1 Prepare the Follow the steps listed here to prepare the EF400 for calibration of the Signal levels EF400 A 1 Power down the EF400 2 Ifyou have not already done so connect the microphone or mixer to the MIC INPUT and the room speaker amplifier or powered speaker to the SPEAKER OUT PUT 3 Ifyou have not already done so connect the terminal equipment to the REMOTE INPUT and REMOTE OUTPUT as shown in Figure 2 4 Turn the volume of the amplifier powered speaker down to zero 5 Loosen the CHASSIS LID SCREW in the upper middle of the backpanel and slide the LOCK BAR down 6 Slide the top cover back to expose the line of trimp
9. 7 EF400 USER M ANUAL echo cancellers force the user to store the room characteristics after the initial conver gence This compensates for the fact that the echo canceller is not capable of converg ing quickly to major acoustical changes The EF400 does not have this flaw Other AECs compensate for inadequacies in their state machines by restricting the rate of change and the amount of change that they allow in their adaptive filters This prevents the AEC from going too far out of convergence by adapting too rapidly when it is confused by a major disturbance while allowing it to track relatively minor changes such as a door opening or slow movement of people in the room In this sce nario the AEC must undergo a rapid training procedure to learn the room from its uninitialized state Once trained it adapts to small acoustical changes but major changes require retraining This training usually takes the form of a loud burst of noise or a sequence of tones which the AEC uses to adapt to the gross acoustical characteristics of its environment The most complex and difficult task of an effective AEC is reliably determining when to permit its internal acoustic model to adapt to changes in the acoustic character of the local room Such changes occur when volume levels are changed people move about doors are opened or closed the loudspeaker or the microphone is moved and so on Adaptation should only occur when in receive mode for example whe
10. ECHOFREE EF400 ACOUSTIC ECHO CANCELLER USER M ANUAL Copyright 1999 ASPI Digital All rights reserved Printed in the United States of America Because of technical progress specifications are subject to change without notice EchoFree is a trademark and ASPI is a registered trademark of ASPI Digital ASPI Digital The Sound of DSP 1720 Peachtree Street NW Suite 220 Atlanta GA 30309 2439 404 892 3200 www echofree com Technical Support 404 892 3200 help aspi com EF400UM 0100 99 EF400 USER MANUAL IntroductlOn ASSES CO cci mee 1 1 12 12 2 2 2 2 2 2 2 2 2 2 2 2 2 e RU OU RR UD ENSE PR PUE 4 EF400 Front and Rear Panels de net et tao e RR ERROR 5 Preparethe Room eR 12 2 1 0 0000000 B id 6 Selecta Mounting Locanto oiiaao ee err Pr Rer RR EROR EORR eR 6 Connect Equipment ette eeu e EXE e Kho AEN Re Ee Eee eR 6 Conficuration Setting the Bandwidth WE 8 Setting the Run Setup Switch eese ees eese nente entente ener enne 8 Setting the Phantom Power Switch eee eese 8 Calibration mer 9 About Signal 9 Calibration sic oe ENSIS eI cig sates N e AREE ea 11 Calibration Verification oe Ree pese eee bees Lets 16 CVO AUTO mer 1 1 2 1 1 2 12 121212 2 2 1 t 10 77 The M te B lton Se emu 17 Re
11. HNICAL SPECIFICATIONS MECHANICAL SPECIFICATIONS Dimensions Weight Connectors ELECTRICAL SPECIFICATIONS Power Power Consumption Room and Remote Line Inputs Room and Remote Line Outputs Playback Input Record Output Microphone Input mic level Headroom Phantom Power PERFORMANCE SPECIFICATIONS Frequency Response Total Cancellation Convergence rate Echo cancellation span 8 15 207mm W x 8 40 213mm L x 1 57 40mm H 1 2 rack unit 2 Ib 1 kg 4 wire XLR inputs outputs Aux RCA phono External transformer supplied 100 240VAC 47 63 Hz SW balanced bridging gt 10 kQ input impedance 4 dBu nominal level adjustable to 20 dBu balanced 50 designed to drive gt 600 inputs 4 dBu nomi nal adjustable to 20 dBu unbalanced gt 10 kO input inpedance 8 dBu nominal level unbalanced 75 output impedance designed to drive gt 10 inputs 8 dBu nominal level balanced gt 10 kQ input impedance 30 dBu nominal adjustable to 60 dBu 18 dB 24 V switch selectable 125 7 250 Hz 2 dB Selectable to 3 4 kHz bandwidth 65 dB 30 dB sec 200 ms ASPI Digital The Sound of DSP 23 COMPLIANCE FCC Part 15 24 Warning EF400 USER M ANUAL The EF400 is compliant with the ITU G 167 recommendations for acoustic echo can cellers CE requirements and FCC part 15 requirements This equipment has been tested and found to co
12. ODEC or EF200 input Make sure the CODEC or EF200 is turned on Make sure everything on the remote end is working properly Make sure the cables are not broken Check the cable pinouts ASPI Digital The Sound of DSP 19 EF400 USER M ANUAL RESIDUAL ECHO Reverberation vs Echo Low Remote Level and or High Loudspeaker Gain 20 Make sure the microphone mixer if present is on and that the volume is up Make sure the microphone is plugged into it If the microphone requires phantom power make sure that the microphone mixer is providing it to the microphone Make sure the microphone or mixer is plugged into the MICROPHONE INPUT You may hear residual echo if system levels are not set properly Improper level set tings anywhere in the audio path can introduce nonlinearities that hamper the opera tion of the EF400 If you hear residual echo one of the following conditions may be causing the problem Do not confuse the residual echo of remote speech with the reverberation of local speech Reverberation of local speech is caused when the speech signal arrives at the microphone via several paths the direct path and multiple reflections from surfaces in the room This is a local room phenomenon that gives the speaker s voice a hollow or resonant sound as heard at the remote end Reverberation is not an artifact of the echo canceller It is mainly affected by the dis tance of the microphone from the speech source and by
13. PHONE INPUT LEVEL INDICATOR during normal conferencing conversa tion The first yellow LED should illuminate frequently and the second yellow LED should flicker regularly during periods of louder speech If the MICROPHONE INPUT LEVEL INDICATOR never illuminates beyond one or two green LEDs during normal speech increase the microphone input level If you adjust the MICROPHONE INPUT signal you may need to readjust the REMOTE INPUT signal level to match it Refer to Microphone and Remote Signal Levels do not Match on page 21 and Calibration Verification on page 17 for more information Overdriving the loudspeaker may distort the loudspeaker signal and cause ineffective AEC operation The EF400 relies on the linearity of the acoustic feedback path D A amplifier loudspeaker microphone preamplifier and A D to cancel acoustic echoes If you overdrive the speaker the acoustic reflections picked up by the micro ASPI Digital The Sound of DSP 21 TECHNICAL 9UPPO RT 22 EF400 USER M ANUAL phone do not match the signal fed to the speaker They are distorted copies of this sig nal The EF400 cannot effectively cancel this distorted signal If you suspect the loudspeaker is introducing nonlinearities into the room acoustic path take these steps to minimize its influence on the echo canceller Keep the loudspeaker s volume level at less than three eighths of full scale If higher volume is required the EF400 should operate effective
14. Play Record Room n INPUT REMOTE Figure 2 Connection of typical external equipment to the EF400 Required Connections Certain equipment and connections are required for the EF400 to be fully operational Figure 2 depicts typical connections Complete the following steps to make all the required connections 1 Connect the MIC INPUT to a microphone or to the output of a microphone pream plifier The MIC INPUT accepts balanced XLR type or balanced Phone TRS connectors 2 Connect the SPEAKER OUTPUT to the input of an audio amplifier or powered speaker This output cannot drive an unamplified speaker The SPEAKER OUTPUT accepts a balanced XLR type connector 3 Connect the REMOTE INPUT to the output of your terminal equipment usually a CODEC or the FROM AEC connection on the EF200 Phone Add The REMOTE INPUT accepts a balanced XLR type connector 4 Connect the REMOTE OUTPUT to the input of your terminal equipment usually a Copyright 1999 All Rights Reserved INSTALLATION CODEC or the To AEC connection on the EF200 Phone Add The REMOTE OUTPUT accepts a balanced XLR type connector Important Verify that the EF400 REMOTE INPUT is connected to the output of the CODEC and the EF400 REMOTE OUTPUT is connected to the input of the CODEC 5 Connect the power supply connector to the external power supply i
15. You do not have to calibrate the EF400 each time it is used When calibrated for the particular microphone and CODEC setup the EF400 will provide years of service without recalibration If the signal levels are not calibrated the performance of the EF400 may not be satisfactory When the signal levels are cal ibrated correctly the EF400 easily and automatically handles any type of signals and change in room acoustics for unparalleled echo cancellation performance After calibration the microphone input signal and remote input signal must be at the same nominal signal level If these two inputs differ in nominal level by 6dB or more the performance of the EF400 will be compromised Audio signal levels for the EF400 inputs and outputs are controlled by trimpots which you can see by sliding back the unit s top cover These trimpots are lined up with the appropriate backpanel connector and are labeled viewed from the front and left to right RECORD PLAYBACK REMOTE OUTPUT REMOTE INPUT SPEAKER OUT PUT MIC INPUT and MIC GAIN A plastic trimpot adjuster is shipped with the EF400 to allow the levels to be adjusted The EF400 works with audio equipment requiring signal levels in the range of 4dBu to 20dBu This range covers professional audio levels 4dBu and consumer equip ment levels 8dBu or 10dBV It also allows a further 1208 signal attenuation to 20dBu if required The most commonly used levels 4 8 and 20dBu are labeled
16. and only the first yellow LED on the REMOTE INPUT LEVEL INDICATOR Louder ASPI Digital The Sound of DSP 13 Note Step 5 Calibrate Remote O utput Important Note Step 6 Tape Playback and Record Levels 14 EF400 USER M ANUAL speech will cause the second yellow LED to pulse on and off The level on the indicator will vary as the speech energy from the remote end varies the indicator indicates peak energy in a similar fashion to a VU meter 4 Now speak in a normal voice with the person at the remote end You should still be positioned as described in Step 1 facing the microphone at distance of 1 1 5 meters Observe the MICROPHONE INPUT LEVEL INDICATOR and REMOTE INPUT LEVEL INDICATOR Both indicators should show similar levels of activity in reac tion to passages of similar speech strength If the person at the remote end cannot hear you clearly when you speak at a normal level turn the REMOTE OUTPUT trimpot clockwise towards 4dBu Continue the clockwise adjustment up to 4dBu until they can hear you clearly 5 Ifthe REMOTE INPUT LEVEL INDICATOR consistently illuminates more LEDs than the MICROPHONE INPUT LEVEL INDICATOR turn the REMOTE INPUT trimpot counterclockwise towards 4dBu to compensate If the REMOTE INPUT LEVEL INDICATOR consistently illuminates fewer LEDs than the MICROPHONE INPUT LEVEL INDICATOR turn the REMOTE INPUT trimpot clockwise towards 20 dBu to compensate 6 Ifyou moved your
17. ble to cause residual echo by having too much gain between the loudspeaker and microphone Watch the REMOTE INPUT LEVEL METER and MICROPHONE INPUT LEVEL METER simultaneously during remote speech Both meters should show some activity The microphone activity is caused by the loudspeaker signal picked up by the microphone If the microphone level is much louder there may be residual echoes The gain between the loud speaker and microphone can be reduced by lowering the loudspeaker volume adding acoustical treatment to the room or by moving microphones and loudspeakers to pro vide more isolation Copyright 1999 All Rights Reserved TROUBLESHO OTING Excessive Microphone Preamplification Note Insufficient Microphone Preamplification Note Loudspeaker Nonlinearity See the Calibration section for more information on setting microphone and remote signal levels For the EF400 to adapt effectively saturation overload or clipping must not occur at the A D converter supplying the microphone input Saturation introduces nonlinear signal distortions into what the AEC expects is a linearly echoed version of the remote speech Nonlinear distortion causes a degradation or divergence of the AEC s internal model of the room acoustics In this situation the EF400 cannot effectively cancel room ech oes and a substantial amount of echo may be heard by the remote party You can check for excessive microphone amplification by observi
18. cord and Playback asses i e ee ER EE PERI 17 General Conferencing Guidelines eee eese eene 18 Troubleshooting siti oiii eoi etel L9 No Output to Loudspeakers you can t hear them No Output to Remote End they can t hear you Residual Echo Technical Support Technical Specifications 1 1 1 1 1 1 1 1 1 1 1 1 1 1 oe Senes teen anota e on vus e Warranty Information P 5 00101010101000 1 ASPI Digital Copyright 1999 EF400 USER M ANUAL INTRODUCTION Congratulations About the EF400 User M anual Product Description Warranty Registration Congratulations on your purchase of the EchoFree EF400 Acoustic Echo Canceller AEC By choosing the EF400 you have gained an exceptional communications sys tem that delivers crisp clear audio and efficient comfortable conferencing This manual tells you how to install configure and calibrate the EF400 to function in a hands free conferencing system It also provides information about operating and troubleshooting the EF400 The EchoFree EF400 AEC supports two way conversations in hands free commu nications applications The EF400 eliminates echoes and acoustic feedback that occur when loudspeaker audio is picked up by room microphones Whether you are using the EF400 in a small cubicle or a large conference room all parties can communicate simultaneously without echoes sw
19. eives from the local microphone to remove the reflected loudspeaker signal from the local microphone signal Thus AEC allows full duplex communications over an open microphone loudspeaker combination An AEC must learn the loudspeaker to microphone acoustic response function for the room it is servicing in order to cancel echoes The EF400 AEC does not use noise to train the echo canceller Rather it continuously trains on the normal exchange of speech during the conversation This results in a more natural flow of conversation from the beginning of the meeting AEC adaptation can be roughly divided into two phases large rapid changes are required to adapt to major acoustical changes such as moving to a new room smaller changes are required to adapt to minor perturbations such as people moving and doors opening When an AEC is first powered up in a room or moved to a new location it needs to adapt from its uninitialized state to learn the new acoustics of its surroundings A good AEC has a state machine that adapts to this level of acoustical change quickly and unobtrusively by determining when it is in the receive state and adapting rapidly during that state The state machine of a mediocre or poor AEC is not as decisive or may even make incorrect decisions during this critical phase As a result the AEC remains uncon verged too long or in extreme cases never properly adapts Some manufacturers of ASPI Digital The Sound of DSP 2
20. equipment such as a tape recorder or VCR These connectors are designed for 8dBu nominal signal level Set the trimpots for these connections to 8dBu for most appli cations If these levels prove unsatisfactory for any reason adjust them up or down by several dB Step 7 Install Slide the top cover forward on the EF400 and secure it with the lock bar and chassis EF400 AEC Unit lid screw The EF400 is now ready for tabletop or rackmount installation CA 7 SCREWDRIVER 3 Tabletop Installation The EF400 is equipped with four rubber feet that allow installation on a flat surface such as a tabletop 1 Remove the adhesive backing on the rubber feet 2 Install the rubber feet in the circular cutouts on the EF400 baseplate Rackmount Installation 1 After you complete the configuration and calibration procedures place the EF400 on the ASPI Digital RS200 Shelf 2 Secure the EF400 to the RS200 shelf using four of the small screws 4 40 x 14 provided with the RS200 If one EF400 is to be mounted on the shelf place it in the center If two units are to be mounted mount them size by side 3 If only one EF400 is mounted attach the two small faceplates supplied with the RS200 to each side of the EFA00 Use four more of the small screws to secure the face plates 4 Secure the RS200 shelf to the rack using all four large screws 10 32 x 1 2 sup plied with the RS200 5 The EF400 power supply bloc
21. es are not broken Check the cable pinouts Make sure the SPEAKER OUTPUT is connected to the amplifier or powered speaker input Make sure the amplifier or powered speaker is on and that the volume is at an appro priate level No OUTPUT TO REMOTE END THEY CAN T HEAR YOU Check the MICROPHONE INPUT LEVEL INDICATOR and make sure it displays activity when you speak into the microphone If LEDs show activity when you speak into the microphone the EF400 is receiving the microphone signal This means the remote end is not receiving a signal from the EF400 Check the REMOTE OUTPUT by connecting it to the amplifier or powered speaker turn the speaker down to avoid howling If the speaker emits sound when you speak into the microphone the signal is making it through the EF400 This means there is a problem with the CODEC the CODEC connection or a device on the remote end If the MICROPHONE INPUT LEVEL INDICATOR does not display activity the EF400 is not receiving the microphone signal This means there is a problem with the micro phone or preamplifier If there is no speaker output unplug the mute button If this fixes the problem the mute button is damaged or incompatible with the EF400 If you are not using a microphone mixer and the microphone requires phantom power make sure it is enabled in the EF400 Make sure the phantom power voltage is compatible with the microphone Make sure the REMOTE OUTPUT is connected to the C
22. ge 17 The mute switch turns off the REMOTE OUTPUT while still allowing adaptation It prevents local conversations from being sent to the remote site POWER SUPPLY INPUT Connects to the external power supply CHASSIS LID SCREW Loosen this screw to lower the LOCK BAR open the chas sis and make adjustments to the EF400 LOCK BAR Latches on to the CHASSIS LID SCREW to keep the lid on PREPARE THE ROOM EF400 USER M ANUAL To ensure good acoustics in the room add carpeting curtains or acoustic tiles to the conferencing room Improving room acoustics enhances the performance of the EF400 and the sound quality and intelligibility of local speech Keeping microphones near people and away from loudspeakers and noise sources fans air vents and pro jectors for example also improves the performance of the EF400 SELECT A MOUNTING LOCATION CONNECT EQUIPMENT After verifying that you have all the equipment and material required for the installa tion select a mounting location for the system You can mount the EF400 on a table top or an ASPI Digital RS200 Shelf The RS200 Shelf can support two EF400s mounted side by side or an EF400 and an EF200 Phone Add for using the EF400 with a telephone line Assemble your tools and all required and optional equipment in an area that is conve nient to the mounting location E 00 CODEC hybrid E E mn 0 5 15 MUTE
23. ing your ASPI Digital product we will ship it to you via a surface carrier of our choice at no cost to you If you wish it shipped via a specific carrier at your cost you must arrange it when you obtain the RMA Repair or replacement of your ASPI Digital product is your exclusive remedy This warranty does not cover defects resulting from accidents damage while in tran sit to our service location alterations unauthorized repair failure to follow instruc ASPI Digital The Sound of DSP 25 No User Serviceable Parts State Law Rights 26 EF400 USER M ANUAL tions misuse fire flood lightning acts of God or use in those countries where such use violates Part 779 of the Export Administration Regulations of the United States Department of Commerce If your ASPI Digital product is not covered by our warranty call us at 404 892 3200 or fax us at 404 892 2512 for advice about whether we will repair your ASPI Digital product and for other repair information including charges ASPI Digital in its sole discretion may replace rather than repair your ASPI Digital product with a new or reconditioned one of the same or similar design The repair or replacement is war ranted for 90 days The limited warranties and remedies set forth above are exclusive and in lieu of all other warranties whether oral or written express or implied ASPI Digital specifi cally disclaims any and all implied warranties including without limita
24. itching noises clipping of words or dropout of speech A patented state logic algorithm ensures smooth and natural communications without typical speakerphone performance problems The EF400 employs a subband digital filtering architecture for echo cancellation This architecture provides faster convergence and better performance than other echo cancellers It continually adapts to changes in the environment so that participants can move about freely and volume levels may change during the conversation without adversely affecting communication quality Unlike most other echo cancellers the EF400 requires no training sequence to learn a room s echo response This means there are no annoying tone bursts at the beginning of the conversation After the unit has been installed all you have to do is turn it on No further adjustments are required You can move the speaker or microphone or change rooms without putting the EF400 through a training sequence This is possible because of the EF400 s advanced acous tic echo cancellation technology And it means the EF400 adapts to changes in room acoustics during conversations quickly for consistent performance throughout the conversation In addition to superior echo cancellation the EF400 provides high fidelity audio con nections This allows low noise trouble free interaction with professional or con sumer quality audio equipment Please take a moment to fill out and return your warranty regi
25. k should be placed securely in the base of the rack unit To eliminate any risk of the power cable being pulled out of the EF400 rear panel connector use the plastic Ty Wraps provided with the RS200 to provide strain relief by securing the power cable to the rack upright at the rear of the EF400 Caution Failure to use all four screws to attach the RS200 shelf to the rack may result in uneven loading and cause a safety hazard Caution Ensure that the power supply is securely located such that it cannot become dislodged and fall Such a fall could cause personal injury or equipment failure Caution When mounting an EF400 in a rack consideration should be given to airflow and operating ambient temperatures inside the rack To ensure safe operation of the EF400 ambient operating temperatures inside the rack should not exceed 50 degrees Celsius Allow 2 inches of open space in front of the EF400 and four inches behind the unit for proper ventilation Equipment should not be installed in the rack in such a way as to interfere with ventilation to the EF400 ASPI Digital The Sound of DSP 15 Caution Caution EF400 USER M ANUAL Consideration should be given to the connection of the equipment to the supply cir cuit and the effect that overloading of circuits could have on overcurrent protection and supply wiring Appropriate consideration of equipment nameplate ratings should be used when addressing this concern Reliable earthing of
26. ly at volume set tings of up to 50 percent of full scale At more than 50 percent most audio sys tems and loudspeakers introduce significant nonlinearities The EF400 may not adapt under these conditions and echoes may be heard If the loudspeaker has a bass control lower it Excessive bass can cause a boomy effect that is nonlinear In addition excessive bass may cause substantial mechanical coupling to the microphone through vibrations induced in the hous ings and support structures Increase the separation distance between the microphone and loudspeaker The EF400 handles up to 10dB of acoustic gain between the speaker and the micro phone You may be exceeding this limit if the speaker is pointed directly at the microphone or if the speaker volume is excessive Speaker placement is not crit ical but it should not be pointed directly at the microphone If these troubleshooting guidelines don t resolve the problem you are experiencing with the EF400 please check our web site Aittp www echofree com support for the most current technical support information If you have further questions please con tact us at Applications Engineering ASPI Digital 1720 Peachtree St NW Suite 220 Atlanta 30309 2439 Phone 404 892 3200 Fax 404 892 2512 Email help aspi com Before contacting us please review the warranty and repair policy on page 24 Copyright 1999 All Rights Reserved TECHNICAL SPECIFICATIONS TEC
27. m settings Guaranteed superior workmanship backed by a full two year warranty Extended warranty available EF400 USER M ANUAL INSTALLATION PREPARIN G The EF400 product package includes the following items EF400 User Manual this manual EF400 Acoustic Echo Canceller e External power supply e Warranty registration card e Flat head trimpot adjuster You need the following tools to install and configure the EF400 EF400 User Manual this manual e Small Phillips head screwdriver for opening the top of EF400 e Hand held SPL meter for measuring loudness such as the Radio Shack 33 2050 Sound Level Meter e Small plastic trimpot adjuster for adjusting the electrical signal levels included RESPONSE m ui B iu g 9 2 5 o o Ac je WEIGHTING You need the following additional equipment to create a completely functional sys tem Microphone s e Speaker s e Audio amplifier or amplified speaker CODEC and or EF200 Phone Add Audio cables recorder VCR optional e Mute switch optional RS200 Rack Mount shelf optional 4 Copyright 1999 All Rights Reserved INSTALLATION EF400 FRONT AND REAR PANELS THE SOUND POWER MICROPHONE REMOTE MUTE EchoFree 2 C 2 if EF400 INPUT SPEAKER OUTPUT 5 15 MUTE ROOM INPUT 0 Oa if
28. ment of both the loud speaker and microphone and to changes in loudspeaker volume The system integra tor is freed from the design constraints of most echo cancellers and end users can arrange their space as they desire The specifications of most AECs require an acoustic room gain of OdB or lower This limits loudspeaker output and restricts microphone placement and gain The EF400 AEC can operate at room gains of up to 10dB which allows 10 times greater acoustic power output This permits great flexibility in microphone and loudspeaker placement and volume adjustment Copyright 1999 All Rights Reserved APPENDIX ABOUT AEC CONNECTOR PINOUTS MICROPHONE INPUT The microphone input accepts either XLR or 1 4 Phone balanced male connectors NEUTRIK XLR 1 shield 2 positive signal 3 negative signal 1 4 Tip positive signal Ring negative signal Sleeve shield REMOTE INPUT The remote input accepts an XLR balanced male connector XLR 1 shield 2 positive signal 3 negative signal SPEAKER OUTPUT AND REMOTE OUTPUT The speaker and remote outputs accept XLR balanced female connec tors XLR 1 shield 2 positive signal 3 negative signal RECORD OUTPUT AND PLAYBACK INPUT The record output and playback input accept RCA male connectors RCA positive signal 2 ground MUTE ROOM INPUT The mute button input accepts a 3 5 mm mini mail connector The tip and sleeve should be shorted
29. microphone in Step 1 now move it back to its normal operat ing position This step shows you how to match the remote output level to the remote input level by adjusting the REMOTE OUTPUT trimpot If you are using the EF400 with an EF200 Phone Add turn the REMOTE OUTPUT trimpot to 20 dBu fully counterclockwise E Set the REMOTE OUTPUT trimpot to the same numeric level as you previously selected for the REMOTE INPUT level Turn the REMOTE OUTPUT trimpot until the trimpot slot points to the marks on the EF400 circuit board that correspond to the level you selected on the REMOTE INPUT trimpot Remember that the numeric markings around the REMOTE OUTPUT trimpot are in reverse order to those around the REMOTE INPUT trimpot The input and output audio levels at the remote equipment may not be symmetric because of imbalances in the remote equipment or the interposing communications equipment You can compensate for such imbalances by adjusting the REMOTE OUT PUT level If the audio signal at the remote end is overdriven and distorted after you set the REMOTE OUTPUT level adjust the REMOTE OUTPUT trimpot down counter clockwise If the audio signal at the remote end is too low adjust the REMOTE OUT PUT trimpot up clockwise The tape playback and record levels should not require adjustment Copyright 1999 All Rights Reserved CALIBRATION The TAPE PLAY INPUT and TAPE RECORD OUTPUT interface to consumer grade audio
30. mply with the limits for a Class A dig ital device pursuant to Part 15 of the FCC Rules These limits are designed to pro vide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radi ate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Opera tion of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense FCC Regulations state that any unauthorized changes or modifications to this equip ment not expressly approved by the manufacturer could void the user s authorization to operate this equipment The EF400 also complies with the CE standards EN5008 1 1 EN50082 1 and EN60950 Conformity of the equipment with those guidelines is attested by the CE mark Copyright 1999 All Rights Reserved WARRANTY INFORMATION WARRANTY INFORMATION What is covered For how long What we will do Limitations W hat we ask you to do W hat this warranty does not cover Any defect in materials or workmanship Two years If your ASPI Digital product is defective and returned within two years of the date of purchase we will repair or at our option replace it at no charge to you If we repair your ASPI Digital product we may
31. n the local party is silent and the remote party is talking Inaccurate mode decisions cause the AEC s internal model to diverge and echoes are not effectively canceled Inaccuracies in this decision process can cause another significant problem one that is handled very elegantly by the EF400 In addition to reducing the effectiveness of the echo cancellation inaccurate state or mode decisions may introduce artifacts into the transmitted or received speech signals Words may be clipped or exhibit dropouts Switch loss or center clipping which are nonlinear processes may be applied to a speech signal in the wrong mode This causes chirping or warbling artifacts that can be annoying and distracting This can be noticeable in any mode but particularly in doubletalk both parties talking simultaneously The EF400 AEC features patented state machine logic so advanced that it permits natural undistorted doubletalk as well as enabling fast accurate adaptation State transitions are smooth and nonintrusive and gain during doubletalk is gently and unobtrusively ramped down by a maximum of 3dB The EF400 employs a subband digital filtering technique to achieve faster conver gence than other echo cancellers This allows the EF400 to adapt rapidly and unobtru sively to changing acoustic conditions People can move about freely during the conversation without degrading communications quality The EF400 also automatically adapts to changes in the place
32. ncluded with the EF400 0 ptional You may find these connections useful but they are not required for proper operation Connections of the EF400 Record To record with a tape recorder or VCR connect the TAPE RECORD OUT PUT on the EF400 to the audio input on the recording device This is an unbal anced RCA connector Playback To play back through a tape recorder or VCR connect the TAPE PLAY BACK INPUT on the EF400 to the audio output on the playback device This is an unbalanced RCA connector Mute To add mute capability connect the MUTE ROOM INPUT on the EF400 to a mute button or other switching circuit This is a two conductor mini connector If the switch is closed that is the two conductors of the MUTE ROOM INPUT are shorted the REMOTE OUTPUT is muted If the switch is open the REMOTE OUT PUT is not muted If you do not connect the mute button to the MUTE ROOM INPUT the EF400 is not capable of muting audio Important You can build a mute button using the schematic in Figure 4 on page 17 ASPI Digital The Sound of DSP 7 CONFIGURATION NOTE Important EF400 USER M ANUAL You must configure several options using the DIP switch S7 These options are described below Refer to the EF400 Circuit Board Layout on page 12 for the location of DIP switch S7 You must open the EF400 chassis to access the DIP switches The side of the switch that is down is the side that is selected For instance if the 7 0kHz 3
33. ng the front panel MICROPHONE INPUT LEVEL INDICATOR during a normal conference The first yellow LED should illuminate frequently and the second yellow LED should flicker regu larly during periods of louder speech If the second yellow LED is illuminated con stantly during normal speech or if the red LED illuminates or even flickers reduce the microphone input level If you adjust the MICROPHONE INPUT signal you may need to readjust the REMOTE INPUT signal level to match it Refer to Microphone and Remote Signal Levels do not Match on page 21 and Calibration Verification on page 17 for more information Grossly insufficient microphone gain degrades EF400 performance and weakens the out bound speech power level This has the effect of reducing the signal to noise ratio of the microphone signal which is analogous to raising the background noise level in the room Because this noise is uncorrelated with the echoes within the room the EF400 s ability to adapt and cancel echoes is compromised A second effect of insufficient microphone gain is that the power of the microphone input signal may be substantially lower than that of the remote input signal This reduces the ability of the decision logic to determine whether the AEC should be in transmit receive or double talk mode This effect may reduce the effectiveness of the EF400 in canceling echoes You can check for insufficient microphone preamplification by observing the front panel MICRO
34. ointing towards each other 4 Set the range on the SPL meter to 70dB C weighted fast response Place the SPL Copyright 1999 All Rights Reserved CALIBRATION meter beside the microphone Point the SPL meter toward the loudspeaker 5 Turn on the EF400 you will hear white noise on the loudspeaker and adjust the volume on the loudspeaker until the SPL meter reads 73dB Stand to the side of the SPL meter rather than in front of it or behind it while reading it so that your body does not interfere with the reading 6 Adjust the appropriate trimpot and observe the LEDs on the front panel MICRO PHONE INPUT LEVEL INDICATOR If the MIC LINE switch is in the LINE position turn the MIC INPUT trimpot clock wise e MIC LINE switch is in the MIC position turn the MIC GAIN trimpot clock wise You may need to turn this pot several times Continue to adjust the trimpot until all three green LEDs and only the first yellow LED are illuminated The second yellow LED should not be illuminated it may flicker occasionally Note If adjustment of the trimpot appears to have no effect on the MICROPHONE INPUT LEVEL INDICATOR return to Step 1 and verify that you are adjusting the correct trim pot 7 Move your loudspeaker and microphone back to their normal operating posi tions 8 Set the RUN SETUP switch back to the RUN position The EF400 is now in normal operating mode Important Avoid pointing the microphone directly at
35. ots These trimpots are lined up with the appropriate backpanel connector and are labeled Refer to Figure 3 on page 10 7 Identify the DIP switch S7 in the center left of the EF400 Set the RUN SETUP switch to the SETUP position This generates a white noise signal on the SPEAKER OUTPUT which is used to set the microphone input level when the system is powered up Important Now you are ready to calibrate the EF400 signal levels Do not apply power to the EF400 until directed to do so in the following instructions Step 2 Calibrate You must match the speaker output level to the specified nominal input level of your Speaker O utput powered speaker or amplifier ASPI Digital The Sound of DSP Determine the appropriate nominal signal level for your powered speaker or loudspeaker amplifier The specifications for your powered speaker or amplifier should include the nominal input signal level If you do not have nominal level specifications for your loudspeaker amplifier or if the specifications are unclear use these guidelines If you are using a powered speaker it probably requires a 8dBu input level If you are using an amplifier and the connectors are RCA phono connectors use 8dBu If the connectors are balanced most likely XLR type connectors use OdBu this is half way between the 4 and 8 marks around the SPEAKER OUTPUT trimpot Turn the SPEAKER OUTPUT trimpot until the trimpot slot points to the marking on the EF400 ci
36. rack mounted equipment should be maintained Particular atten tion should be given to supply connections other than direct connection to the Branch use of power strips CALIBRATION VERIFICATION 16 During normal operation a conference observe the front panel MICROPHONE INPUT LEVEL INDICATOR and REMOTE INPUT LEVEL INDICATOR The red LED should not flicker or illuminate on either meter If either red LED illuminates or flickers fre quently reduce the corresponding input level Both signal level meters should exhibit similar behavior The calibration process accommodates a nominal speech level at the room microphone normal speech at 1m to 2m from the microphone During low level speech several green LEDs may illuminate During normal speech in aconference the first yellow LED should illuminate frequently and the second yellow LED should flicker regularly during periods of louder speech Extreme and unusual levels for example a participant shouting into the microphone may over drive the input level and cause the red LED to illuminate This is not cause for con cern unless you expect this condition to be the normal operating mode Similar speech activity levels at the local and remote ends should cause the same number of LEDs to illuminate on both signal strength meters If the REMOTE INPUT LEVEL INDICATOR is consistently lower than the MICROPHONE INPUT LEVEL INDICA TOR adjust the REMOTE INPUT trimpot clockwise toward the 20dBu ma
37. rcuit board corresponding to the nominal level selected in the previous step If the input signal level for your powered speaker or amplifier are specified in terms of dBu or dBm this number corresponds to the numbers 4 0 8 20 printed on the EF400 circuit board If the speaker or amplifier level is 11 EF400 USER M ANUAL Step 3 Calibrate M icrophone Input 12 Important Note Note specified in terms of dBV add 2 to the dBV number to translate it to dBu for example 10dBV corresponds roughly to 8 dBu After the SPEAKER OUTPUT is calibrated you can calibrate the MIC INPUT level In this step you calibrate the mic input level using a 73dB SPL noise signal gener ated by the EF400 You want to illuminate the first yellow LED but not the second yellow LED on the front panel MICROPHONE INPUT LEVEL INDICATOR boy 2 2 5 6 avez SOUND LEVEL METER Ac WEIGHTING You use the built in noise generator and your SPL meter to set the mic input level Extraneous noise such as conversation should not be audible in the local conference room as it would make it very difficult to get consistent readings on the SPL meter and MICROPHONE INPUT LEVEL INDICATOR You use different trimpots to calibrate the MIC INPUT level depending on whether the input signal is line level from a microphone preamplifier or mic level directly from a microphone 1 Locate the MIC LINE switch S9 the MIC INPUT trimpo
38. rk to bring up the level on the REMOTE INPUT LEVEL INDICATOR If the REMOTE INPUT LEVEL INDICATOR is consistently higher than the MICROPHONE INPUT LEVEL INDICATOR adjust the REMOTE INPUT trimpot counterclockwise toward the 4 mark to bring down the level on the REMOTE INPUT LEVEL INDICATOR The remote equipment may be set up using a different procedure and may be produc ing signals at a different level than the nominal input level of your terminal equip ment This would cause your terminal equipment to produce signals lower than its nominal level Thus the setting of the REMOTE INPUT trimpot may differ from the output signal level specifications for your terminal equipment For example your ter minal equipment may specify a nominal output level of 8dBu but you may have to set the REMOTE INPUT trimpot to 20dBu to bring the remote signal to the same level as the local microphone Copyright 1999 All Rights Reserved OPERATION O PERATION TRAININ G THE MUTE BUTTON Note The EF400 operates automatically User interaction is not required unless the optional mute button has been installed Below are instructions for using the EF400 and ensur ing a successful conference Because of the EF400 s superior AEC technology no training sequence is necessary After the EF400 is powered up it automatically adapts to the room s acoustics When pressed the mute button prevents local speech from being transmitted to the REMOTE
39. stration card This infor mation will help us to provide you with better customer support Copyright 1999 All Rights Reserved INTRODUCTION PRODUCT FEATURES ASPI Digital The Sound of DSP Full duplex communications that sounds real and natural with no switching dropouts or speech clipping All parties can be heard simultaneously Based on proven patented technology Automatic training does not require noise bursts or tones for setup Continuous and quick adaptation to changes in room acoustics with a 30dB s convergence rate Howling rejection feedback suppression Long tail time 200 ms for even difficult rooms Operates with up to 10dB room gain Supports 3 5kHz and 7kHz speech and audio communications switch select able Supports muting without disabling AEC adaptation Balanced professional line level input and output permit direct connection to CODECs and other professional quality equipment Connects to the EF200 Phone Add to make a complete teleconferencing unit Accepts mic level input switch selectable Unbalanced record input and playback output for connecting external equipment Small footprint fits easily in rollabout carts or on rack tray Easy set up After input and output levels are calibrated operation is completely automatic Tamper proof No external level controls for unauthorized users to disturb Continuous and quick adaptation to new environments Does not require memory to store roo
40. t I PLAY RECORD REMOTE TAPE 6 7 8 9 10 11 12 Figure 1 The front and rear panel of the EchoFree EF400 1 R 10 11 12 13 14 ASPI Digital The Sound of DSP POWER INDICATOR When LED is green power is on MICROPHONE INPUT LEVEL INDICATOR Displays microphone input signal level See page 12 REMOTE INPUT LEVEL INDICATOR Displays remote input signal level See page 13 MUTE INDICATOR When the LED is blue local audio is not sent to the remote connection INPUT Connects to a mic mic preamplifier or mixer Provides phantom power to condenser microphones Configured via the internal phantom power switch See page 8 SPEAKER OUTPUT Connects to an audio amplifier or powered speaker Line level output cannot drive a speaker without an amplifier REMOTE INPUT Connects to the output of a CODEC or EF200 Phone Add REMOTE OUTPUT Connects to the input of a CODEC or EF200 Phone Add TAPE PLAYBACK INPUT Connects to the output of a tape recorder VCR or other recording device This signal is sent to the remote output as well as the speaker output See Figure 5 on page 17 TAPE RECORD OUTPUT Connects to a recording device Signals from the remote and mic inputs both ends of the conversation go to the recording device See Figure 5 on page 17 MUTE ROOM INPUT Connects to the mute switch not included but an example circuit is shown in Figure 4 on pa
41. t and the MIC GAIN trim pot They are to your right and near the back of the circuit board in line with the MIC INPUT connector e Ifyou are using a microphone mixer or preamplifier set the MIC LINE switch to the LINE position e Ifyou are connecting a microphone directly to the EF400 set the MIC LINE switch to the MIC position If the MIC LINE switch is in the LINE position you will be adjusting the MIC INPUT trimpot to a range between 20dBu and 4dBu input signal level If the MIC LINE switch is in the MIC position you will be adjusting the MIC GAIN trimpot to a range between 15dB and 60dB gain This level accommodates microphone signal levels between 33dBu and 80dBu 2 Turn the appropriate trimpot to its minimum setting MIC LINE switch is in the LINE position you will use the MIC INPUT trim pot for input level adjustment Turn the MIC INPUT trimpot fully counterclock wise to the 4 position Ifthe MIC LINE switch is in the MIC position you will use the MIC GAIN trimpot for input level adjustment Turn the MIC GAIN trimpot counterclockwise several times this is a multi turn pot 3 Position the room microphone so that no people or objects are between it and the loudspeaker Be careful not to stand directly between the loudspeaker and the microphone while adjusting the EF400 The microphone should be approxi mately 1m from the loudspeaker if possible and the loudspeaker and the micro phone should be p
42. the resonances of the room While reverberation can be unpleasant it is not compensated for by the AEC which only removes reflections of remote speech You cannot remove the effects of reverberation by changing the EF400 s settings but you can minimize reverberation by moving microphones closer to speakers and if necessary adding acoustical treatment to the room If multiple microphones are open it may be necessary to use an automatic microphone mixer to reduce reverbera tion The most common cause of poor echo cancellation performance is caused by a low REMOTE INPUT level from the CODEC Generally if the remote level is too low this is compensated by increasing the gain to the loudspeaker This results in a much louder signal being returned to the microphone than is being received on the remote end This large level imbalance causes residual echo because it looks like there is much more local audio than remote audio it looks like the people in the room are talking You can check for low remote input signal levels by observing the REMOTE INPUT LEVEL INDICATOR during a normal conference The remote speech should cause one yellow LED to flicker Make sure you are looking at the REMOTE INPUT LEVEL INDI CATOR and not the MICROPHONE INPUT LEVEL INDICATOR If the remote input level is too low increase the gain on the Remote Input trimpot and lower the gain to the loudspeaker Even with a reasonable remote input level it is still possi
43. this can lead to howling Howling is a condition in which the loudspeaker output becomes a loud howl Howling is extremely unpleasant to the human auditory system and it can cause severe damage to the audio equipment Typical inexpensive speakerphones simply avoid these problems They provide only half duplex communication links meaning that only one end has a communication path at any given time The decision of which party should get the active link is deter mined by the signal energy at each end When one end is active the other end cannot become active until the signal level at the first end drops There are many drawbacks to this system For example a talkative individual can monopolize the line and pre vent anyone else from getting a word in edgewise Another drawback is that the acoustic gain of the system must be limited to estimate the local signal energy This is so that energy in the loudspeaker signal is not perceived as local signal energy Acoustic echo cancellation actively removes the reflected echo from the signal picked up by the microphone before transmitting the echo canceled signal to the remote end It does this by forming an internal model of the acoustic transfer function between the signal fed to the loudspeaker and that picked up by the microphone and applying this model to the signal that the AEC receives from the remote end This processed ver sion of the remote signal is then subtracted from the signal that the AEC rec
44. tion the war ranties of merchantability and fitness for a particular purpose This product contains no user serviceable parts Please contact ASPI Digital for repairs Attempts to repair this product by an unauthorized technician will void your warranty This limited warranty gives you specific legal rights and you amy have other rights that may vary from state to state Copyright 1999 All Rights Reserved APPENDIX ABOUT AEC APPENDIX ABOUT AEC Effective hands free communication involves the use of a microphone to pick up the local speech signal and a loudspeaker to project the speech input from the remote site There are several problems associated with having a microphone and loudspeaker enabled at the same time In addition to picking up the local speech signal the micro phone also picks up reflections of the loudspeaker output signal The speech signal from the remote end is amplified and passed to the loudspeaker From here it is pro jected out into the local room and reflected back into the microphone after being col ored by the acoustic character of the room and all its occupants This reflected signal is perceived by the listener at the remote end as echo It can be annoying and extremely distracting and may even render sensible conversation impossible If this feedback of the reflected signal is strong enough and if there is feedback from the remote end for example using an open loudspeaker microphone combination
45. use new or reconditioned replace ment parts If we choose to replace your ASPI Digital product we may replace it with a new or reconditioned one of the same or similar design The repair or replacement is warranted for either a 90 days or b the remainder of the original two year warranty period whichever is longer ASPI Digital shall not be responsible for special incidental indirect or consequential damages resulting from any breach of warranty or under any other legal theory including but not limited to loss of profits downtime goodwill damage to or replace ment of equipment and property and any cost of recovering reprogramming or reproducing any program or data stored in or used with ASPI Digital products Some states do not allow limitations on how long an implied warranty lasts or the exclusion of incidental or consequential damages so the above exclusions or limita tions may not apply to you To obtain warranty service for your ASPI Digital product call us at 404 892 3200 or fax us at 404 892 2512 and we will issue a Return Material Authorization number RMA Use the original packaging materials to return the product Ship the product prepaid to ASPI Digital Attention Warranty Repair RMA Must be on package 1720 Peachtree Street NW Suite 220 Atlanta Georgia 30309 2439 USA Please be sure to include your name company address phone number and a descrip tion of the problem After repairing or replac
Download Pdf Manuals
Related Search