Vortex Media VTX 1000 - Manual (Page 58)

amplifier. Inputs A, B, and C need to be assigned to Outputs 1-4 and Y. By default, Inputs 1-8 are routed to
Output's A and W. Note that since Inputs 1-8 are microphones, the cross-points are colored blue to
indicate that they are gated to Outputs 1-4, B, and W.
Inputs B and C are attenuated by 3 dB to Outputs 1-4, A, and R1 because if the left and right channels are
mono, both channels will increase 6 dB in gain
2 . Inputs B and C 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.
Inputs A, B, and C and Output A are set to +10 dB and -10 dB respectively. Please refer to the section
entitled “Gain Structure” under the W
IRING THE S OUND S TATION VTX 1000 TO A V ORTEX DEVICE heading for more
information as to the reasoning behind the gain levels.
The outputs W and Y are signals that will be sent over the EFBus to the Vortex EF2241. See the section
entitled Conference Composer Layout Vortex EF2241 to find out how to take those signals from the bus and
send them to the telephone line and the interface module.
In order to properly reinforce the local speech, we have used cross-point attenuation to achieve a good
listening level in all zones. Remember that the goal of sound reinforcement is to permit the local listeners
to still "localize" to the local talkers while using the reinforced audio to improve the overall intelligibility of
the local speech.
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,
SoundStation VTX 1000, and program audio from the local microphones. Note that local microphones are
not included in the Reference Signal even though we are reinforcing them.
Local Microphones should NEVER be included in the reference signal!
2 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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