Calrec ALPHA - Paths and Ports

CALREC Putting Sound in the Picture 11
Paths and ports
On an analog desk, the channel inputs
are physical connections to the channel
module or card. They are fixed. Channel
1’s input is always channel 1’s input (even
though it may be possible to control
channel 1 from a different fader). Every
channel will probably have both a mic and
a line input, even though most will only use
one of them at any one time.
In a digital desk, there are two basic types
of input: mic/line and digital. However,
it is not necessary to provide both types
for every channel, as only one input will
be used at any one time. To provide both
types for each channel would increase the
cost, size and power consumption of the
desk unnecessarily.
Instead, a “pool” of each type is available,
plus an internal matrix to allow any of
them to be connected to any channel.
This provides more flexibility than is
possible with analog designs. The
matrix can be thought of as an electronic
patch-bay with the advantage that any
connections made will be stored with the
console’s memories. A similar matrix and
“pool” is provided for the outputs which is
also stored with the memories.
Each channel can select from two inputs
(1 and 2), which can be any combination
of mic/line and digital. Both inputs can
be set up independently, using separate
input controls (input gain, phase reverse,
phantom power, etc). The switching
between the two inputs takes place after
these controls.
The basic terminology is that channels,
groups and mains are referred to as
“paths” within the digital processing
system, and the inputs and outputs are
referred to as “ports” through which the
audio signals have to pass. Ports are
connected to paths via the matrix.
All ports are optional, including those
for the monitoring. The system can be
supplied with any combination of mic/line
and digital ports.
Port labels
During installation, all the ports on the
system are labelled to match the studio
wiring. Some rules are imposed on this
labelling:
Inputs and outputs should be labelled
•
in pairs.
The label must be no more than six
•
characters
Each port must have a unique label,
•
but an input port can have the same
label as an output port.
Inputs and outputs are labelled in pairs for
use with any type of signal; mono, stereo
or surround. As digital inputs and outputs
are wired in pairs and it makes sense to
deal with all the inputs and outputs in the
same way.
The system automatically adds a left
(
L
) and right (R) suffix to the label to
distinguish the two halves of the pair, or an
LR suffix when the pair is used together.
The pairs can be used either for two mono
signals, or a stereo signal, or parts of a
surround signal. This includes the digital
ports if the external circuit allows them to
be used for two mono signals.
Those inputs or outputs which are
dedicated externally to mono signals only
(telephone lines, mono reverbs, mono
distribution feeds, etc), can be specified as
being mono. In this case, the two halves
of the pair have separate labels and the
L
& R suffixes are not applied. Inputs and
outputs labelled in this way cannot be
connected in pairs to stereo paths.
Port lists
In addition to labelling, each port may
be allocated to one of a number of lists
using the Options - Port List screens.
This allows inputs and outputs which are
wired for similar purposes to be grouped
together for selection. Each list can
contain a mixture of normal inputs or
outputs (labelled in pairs) and inputs or
outputs dedicated to mono signals.
The lists can be sorted into the order
in which they appear on the selection
screens. The lists will appear in the
same order on the I/O Matrix panel and
I/O screens. It is possible to restrict
the lists which appear on the I/O Matrix
panel using the Options - Misc screen.
This ensures that only the relevant lists
are immediately available at the user’s
fingertips. All lists are always available on
the I/O screens.
PATHS AND PORTS