Polycom SoundStructure C16 Design Manual page 521

The motivation for using virtual channels is both to allow the control system
programming to start before the physical wiring may be known and to make
the control system programming re-usable across different installations
regardless of how the system is wired. Virtual channels allow third-party con-
trol system code to be easily re-used because the controller code controls the
SoundStructure devices through the virtual channel names, not the underly-
ing physical input and output that a particular channel is connected to. Virtual
channels make the solution more portable and reusable because the control
system doesn't need to know which physical input or output the signal is con-
nected to, it only needs to know the virtual channel name. The use of virtual
channels should also improve the quality of the control system code since it is
more difficult to confuse "Podium mic" vs. "VCR audio" in the code than it
would be to confuse input 7 on device 2 vs. input 9 on device 1. The clarity and
transparency of the virtual channel names should reduce the amount of
debugging and subsequently reduce the amount of time to provide a fully
functional solution.
For instance, if a virtual channel were called "Podium mic" then the control
system code would control this channel by sending commands to "Podium
mic". It would not matter to the control system if on one installation "Podium
mic" were wired to input 1 and on another installation "Podium mic" was
wired to input 7. The same control system code can be used on both installa-
tions because the SoundStructure devices would know which underlying
physical channel(s) are part of the virtual channel definition. By using the
same API commands on different installations that refer to "Podium mic", the
control system code is insulated from the actual physical connections which
are likely to change from one installation to the next.
Virtual channels are a high-level representation that encompasses information
about the physical channel and are used to configure and control the underlying
physical channel(s) without having to know which physical input or output the virtual
channel is connected to after the virtual channel has been defined.
Within SoundStructure Studio and any third-party controller code, virtual
channels are the only way to configure and control the underlying physical
channels. The physical input and output channel numbering described in the
previous section is used only in the definition of virtual channels so that the
virtual channel knows which physical channel(s) it refers to.
A benefit of working with virtual channels is that stereo signals can be more
easily used and configured in the system without having to manually config-
ure both the left and right channels independently. Using virtual channels that
represent stereo physical signals reduces the chance of improper signal rout-
ings and processing selections. The result is that both designs and installations
can happen faster and with higher quality.
Command Protocol Reference Guide
A - 5