Extra Information

Application Note: 121 EF1210TEC Addendum
ASPI Digital - The Sound of DSP 2
Generating Mix Minus with the EF1210TEC
A system using an EF1210TEC can be configured to generate a mix minus. This may be nec-
essary if the system is used with a bridge or MCU that does not have mix minus. 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 micro-
phones) 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.
Using the EF1210TEC in High/Low Delay Applications
In some applications, the signal from another site may arrive from two different paths with dif-
ferent 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 band-
width 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.
Figure 2a: Mix Minus Configuration Figure 2b: High/Low Delay Configuration
8-channel
Automixer
In 1
In 2
In 3
In 4
In 5
In 6
In 7
In 8
Direct Out 1
Direct Out 2
Direct Out 3
Direct Out 4
Direct Out 5
Direct Out 6
Direct Out 7
Direct Out 8
Aux Master Out
EF1210TEC
TEC Input
In 2
In 3
In 4
In 5
In 6
In 7
In 8
TEC Out
Out 2
Out 3
Out 4
Out 5
Out 6
Out 7
Out 8
AEC Ref
TEC Ref
To CODEC
Room Audio
Amix In
Record
To TEC Ref
Pla
y
Video
CODEC
Line In Line Out
EF1210TEC
TEC Input
In 2
In 3
In 4
In 5
In 6
In 7
In 8
TEC Out
Out 2
Out 3
Out 4
Out 5
Out 6
Out 7
Out 8
AEC Ref
TEC Ref
To CODEC
Room Audio
Amix In
Record
To TEC Ref
Pla
y
8-channel
Automixer
In 1
In 2
In 3
In 4
In 5
In 6
In 7
In 8
Direct Out 1
Direct Out 2
Direct Out 3
Direct Out 4
Direct Out 5
Direct Out 6
Direct Out 7
Direct Out 8
Aux Master Out
Low Delay
Video CODEC
Line In Line Out
Hi
g
h Delay
Video CODEC
Line In Line Out
Line Mixer
In 1
In 2
Master Out