
FAA20 Embedded NEXCOM Vocoder
Board Manual
This manual has been prepared for the Federal Aviation Administration.
FA100-00107 (March 2004) – Rev 1.0.0 Page 24
5.3.2 Linear Voice Mixer
The linear voice mixer controls the flow of linear voice through the FAA20.
The mixer has five ports: the analog audio port (AUD), the digital PCM port
(PCM), the vocoder port (VOC), the tone generator port (TON), and the
external communication port (COM).
The mixer supports weighted signal summing with saturation control. For
example, if the PCM port is connected to the vocoder, the AUD port can be
configured to sum the PCM TX and RX signals to provide full-duplex audio
monitoring.
The mixed signals are first multiplied by a weighting factor before
summation. The weighting factor is entered as Q1.15 hexadecimal
formatted value; thus, the range is from 0x0000 (off) to 0x7FFF (unity gain).
Figure 10: Linear Voice Mixer
When controlling the mixer, all transmit and receive signal directions are
referenced at the mixer. In the diagram above, only a receive mixer port is
shown for the tone generator (TON). While an output mixer is provided for
the port, it does not connect to anything (dead-ends) and is thus not shown.
Port
PCM
COM
Port
Port
Port
Port
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