Extra Information
Application Note: 121 EF1210TEC Addendum
ASPI Digital - The Sound of DSP 3
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.
C
ONFIGURING
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.
C
OMMAND
S
ET
C
HANGES
There are three new RS-232 commands in the EF1210TEC. They are TDCD, TDCMIN, and
TDCMAX (the acronym TDC is used because these commands deal with the properties of the
Transmission Delay Compensator as described in the introduction to this addendum). As with
the EF1210, the device type of the EF1210TEC is C.
The TDCD command queries the delay detected by the Transmission Delay Compensator.
This command is used for queries only. For example, the command C00TDCD? queries the
delay detected by the EF1210TEC with device ID 0. The command response contains a delay
value in milliseconds (accurate to within a few milliseconds). If the EF1210TEC were to
return C00TDCD500, the delay detected by the Transmission Delay Compensator is about 500
milliseconds.
The TDCMIN and TDCMAX commands set the minimum and maximum delay over which
the Transmission Delay Compensator will search fo r echoes. Reducing the search range may
cause echoes to be found and cancelled more quickly. 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 Transmis-
sion 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 delay is set in milliseconds. Examples of commands are
C00TDCMIN250 and COOTDCMAX750. The current settings can be queried with a ques-
tion mark as the argument.