Vortex Media VTX 1000 - Manual (Page 90)

Inputs C and D are attenuated by 3 dB to Outputs D, Y, and R1 because if the left and right channels are
mono, both channels will increase 6 dB in gain
4 . Inputs C and D are reduced by 10 dB to Output B and T
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.
We will set Output C 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!
Output Filters
4 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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