Vortex Media VTX 1000 - Manual (Page 37)

Matrix Mixer
The matrix mixer will need to be changed from the default settings in order to use Output A for the Video
Codec, Output B for the Interface Module, Output C for the Amplifier, and Output D for the Subwoofer.
Inputs 1-8 need to be assigned to Outputs A and B so that the people on the far end of a SoundStation VTX
1000 or video codec call can hear the local microphones. The cross-points are colored blue to indicate that
they are gated to Outputs A and B.
The Interface Module (Input B) needs to be assigned to all outputs except Output B. If Input B is assigned
to Output B, then you will create a loopback inside the Vortex EF2280. This will cause the far end of the
SoundStation VTX 1000 to hear an "echo" of themselves although it is an electronically created echo and
not an acoustic echo. The same logic applies to the video codec (Input A / Output A).
Inputs C and D are attenuated by 3 dB to Outputs B, C, D and R1 because if the left and right channels are
mono, both channels will increase 6 dB in gain
1 . Inputs C and D are reduced by 10 dB to Output A because
if a program source is mixed at 0 dB with local speech, it may be difficult for the remote person on the
telephone to distinguish between the program audio and the local speech due to the frequency limitations
of the telephone network. By attenuating the program audio, you "bias" the audio sent to the telephone in
favor of the local speech.
In this example, we will assume that the video codec and program audio outputs are designed to send
and/or receive a consumer level signal. Therefore, Inputs A, B, C, and D and Outputs A and B will be set to
+10 dB (Inputs) and -10 dB (Outputs) respectively. Please refer to the section entitled “Gain Structure”
under the W
IRING THE S OUND S TATION VTX 1000 TO A V ORTEX D EVICE heading for more information as to the
reasoning behind the gain levels.
Output D will be set to -30 dB in order to protect the subwoofer from "bottoming out" on high-amplitude
transient sounds.
The output R1 is our Acoustic Echo Canceller (AEC) reference signal. This signal is what the internal AEC
uses to remove from the local microphones. In our example, we will remove the codec, telephone hybrid
audio, SoundStation VTX 1000 audio, and program audio from the local microphones.
Local Microphones should NEVER be included in the reference signal!
1 If two signals with an amplitude of 1V peak-to-peak each are added together, the summed signal’s amplitude will be 2V peak-
to-peak. In terms of decibels, that can be expressed as 20*log (2V / 1V) which equals 6 dB).
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