User manual POLYCOM EF1210TEC ADDENDUM TO THE EF1210

[. . . ] EF1210TEC ADDENDUM TO THE EF1210 USER MANUAL Since the EF1210TEC is largely based on the EF1210, most of the information in the EF1210 User Manual applies to the EF1210TEC. This document describes the TEC features, and the difference between the operation and configureation of the EF1210TEC and the standard EF1210. INTRODUCTION The EF1210TEC is a unique product that is designed to cancel echoes caused by the transmission network as well as acoustic echoes in the local room. There are a total of eight echo cancellation channels on the EF1210TEC. [. . . ] That is, if the bridge sends the local site's audio back to itself. When the EF1210 is used in this type of application, it will remove its own audio from the incoming signal, while allowing audio from other sites to come through. To generate a mix minus, send the mix of all transmitted audio (including all local microphones) to the TEC Reference input. This will send local audio to the remote sites, and give the TEC a reference. 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. [. . . ] 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. The current settings can be queried with a question mark as the argument. ASPI Digital - The Sound of DSP 3 [. . . ]