User manual POLYCOM EF1210TEC ADDENDUM TO THE EF1210

[. . . ] Seven channels of the EF1210TEC behave as normal Acoustic Echo Cancellation (AEC) channels. One channel is a Transmission Echo Cancellation (TEC) channel. The Transmission Delay Compensator (TDC) determines the amount of delay in the echo signal. [. . . ] To generate a mix minus, send the mix of all transmitted audio (including all local microphones) to the TEC Reference input. Then connect the To CODEC output to the video codec. This will send local audio to the remote sites, and give the TEC a reference. Bring the output of the video codec into the TEC Input. The TEC will cancel any delayed echo from the codec signal and pass it on to the TEC Out. This can be sent to the AEC Reference (this signal now contains audio from the remote sites) and out into the room. The other AEC channels will use this reference to prevent acoustic echo from being sent back out onto the network. TEC Input AEC Ref TEC Ref Play Amix In TEC Out To CODEC Room Audio Video CODEC Line In Line Out TEC Input AEC Ref TEC Ref Play TEC Out To CODEC Room Audio Record To TEC Ref In 1 In 2 Master Out Line Mixer Record Amix In To TEC Ref EF1210TEC In 2 In 3 In 4 In 5 In 6 In 7 In 8 Out 2 Out 3 Out 4 Out 5 Out 6 Out 7 Out 8 In 1 In 2 In 3 In 4 In 5 In 6 In 7 In 8 Direct Out 1 EF1210TEC In 2 In 3 Direct Out 2 In 4 Direct Out 3 In 5 Direct Out 4 In 6 Direct Out 5 In 7 Direct Out 6 In 8 Direct Out 7 In 8 Direct Out 8 Direct Out 8 Out 8 In 7 Direct Out 7 Out 7 In 6 Direct Out 6 Out 6 In 5 Direct Out 5 Line In Line Out Out 5 In 4 Direct Out 4 Out 4 In 3 Direct Out 3 Out 2 Out 3 In 1 In 2 Direct Out 1 Direct Out 2 High Delay Video CODEC 8-channel Automixer Aux Aux Master Out 8-channel Automixer Master Out Low Delay Video CODEC Line In Line Out Figure 2a: Mix Minus Configuration Figure 2b: High/Low Delay Configuration Using the EF1210TEC in High/Low Delay Applications In some applications, the signal from another site may arrive from two different paths with different delays. This is not a typical echo problem in which local talkers hear themselves return through the system. Rather, they will hear talkers from another site twice, possibly separated by several hundred milliseconds. This may occur if some sites are communicating with each other over wide bandwidth connections, and also with a larger number of sites on a low bandwidth bridge. The high bandwidth sites may communicate with each other over both the wide bandwidth and narrow bandwidth networks. Figure 2b shows how this type of system may be connected. ASPI Digital - The Sound of DSP 2 Application Note: 121 EF1210TEC Addendum Systems with More Than Seven Microphones If more than seven microphones are needed, one or more EF1210s may be added to the system to provide echo cancellation on each microphone channel. In general, only one EF1210TEC is needed in the room, and standard EF1210s may be used for additional microphones. CONFIGURING THE TEC The AEC channels of the EF1210TEC can be calibrated and configured as described in the EF1210 User Manual. The EF1210TEC may be configured as a standard EF1210 by setting the DIP switch labelled "Reserved" next to the Device ID 16 DIP switch. When in the off position, the EF1210TEC behavior will be selected. In the on position, the standard EF1210 behavior is selected. COMMAND SET CHANGES There are three new RS-232 commands in the EF1210TEC. [. . . ] For instance, if you know the echo is delayed somewhere between 600-800 milliseconds, you can set TDCMIN to 500 ms, and TDCMAX to 1000 ms. This will allow echoes to be found more quickly than if the Transmission Delay Compensator had to search over the entire 2 second range. It is important not to set the range too narrowly, because if the delay falls outside of the search range, the TEC will not be able to cancel echoes. [. . . ]