Cadac’s MegaCOMMS digital audio network has been designed to meet the requirements of the most challenging applications. MegaCOMMS is a robust, TDM (time division multiplex) system.
Control data is embedded within the data stream, so that no audio channels have
to be sacrificed for this purpose. The high bandwidth available means that the
current implementation of MegaCOMMS can carry 128 channels of 24-bit, 96 kHz
audio, plus control data, plus clock, bi-directionally, up to 150 metres via a
pair of RG-6 coaxial cables.
In addition to audio and control data, MegaCOMMS provides
for accurate, phase-aligned clock distribution, by embedding timing markers in
the data stream. This allows reliable, low-jitter synchronisation of all
hardware elements within a network.
The simplest implementation of a MegaCOMMS network is the
straightforward console-stagebox configuration. In this application, the
console provides the clock and the stagebox synchronises itself once the
connections are made. Total through-system propagation delay for this system,
including all console processing and A-D / D-A conversions is an astonishing 37
samples (@ 96 kHz), or just under 400us. This compares with the many
millisecond propagation delays usually found in most other similar systems.
larger, true audio networks, a MegaCOMMS router is required which provides
low-jitter clock synchronisation and flexible routing capability for up to 3072
channels of 24-bit, 96 kHz audio. The addition of a router into a system only adds
an additional sample (approximately 10us) of propagation delay. MegaCOMMS is
also capable of providing automatic fail-over to redundant spare connections,
so providing peace-of-mind for critical applications. Most Cadac MegaCOMMS
devices (consoles, large-format stageboxes and network bridges) support
dual-redundant connections, with automatic seamless change-over in the event of
The hardware “hub” for a large-scale network is the Cadac MegaCOMMS router – the CDC MC Router. This device has 12 pairs (send and return) of MegaCOMMS ports, easily identifiable from glowing colour coded BNC sockets. The MegaCOMMS router can connect up to 12 MegaCOMMS devices, and a MegaCOMMS device can be a console, stagebox or network bridge. The format of the network is that of a star-type. Depending upon the programming of the router this can be a single or dual-redundant star configuration. Routing maps (up to eight pre-sets) are installed into the router from a laptop computer via a standard RJ45 network port. Any of the eight map pre-sets can easily be selected either from a front panel mounted rotary switch or from a dedicated hardware remote control.
The CDC MC Router also has the useful function of providing “gain compensation” in that if any of the connected mic amps have their analogue gain adjusted, the router will automatically compensate for the change in audio level to any and all other devices connected. This gain compensation process takes just a single sample (about 10us.) for the router to make the necessary adjustment, and so is completely inaudible in operation. This facility allows a stagebox’s analogue inputs to be shared between a number of consoles, and for multiple consoles to be connected to a common set of I/O in order to provide multiple mixing systems or multiple fully dual-redundant systems. In these large scale applications, the MegaCOMMS router provides clock for all consoles and I/O devices.
Cadac have also designed network bridging devices to enable
MegaCOMMS to connect to other protocols. The network bridges feature
dual-redundant power supplies and dual-redundant connections to other MegaCOMMS
units, as well as asynchronous sample-rate conversion to other popular
protocols such as MADI (AES10), via the CDC MC MADI Newtork Bridge, and DANTE via the CDC MC Dante Network Bridge.
MegaCOMMS networks are clocked at 96 kHz, but Cadac do
provide for SRC (sample rate convertor) to other clock speeds and conversion to
more widely adopted protocols such as MADI and Dante.
Below is a diagram showing the potential network capability of the CDC MC Router:
The above diagram has 128 analogue inputs shared between four
consoles, which can be configured either as four discrete mixing systems, or
two redundant console pairs. The example also shows audio distributed to remote
broadcast and recording facilities via MegaCOMMS to MADI and Dante network bridges. The CDC MC Router
provides gain compensation for all audio streams should any analogue input
gains be adjusted during the performance, and can be pre-programmed with up to
eight different routing maps, which can be selected from remote switching
panel. All RG-6 coaxial cables can be up to 150 metres and the optical link up to 2 kilometres.
This video provides an overview of Cadac's MegaCOMMS digital audio network
- Up to 128 bi-directional channels of 96 kHz / 24-bit audio
- Latency on a MegaCOMMS link is a single sample @96 kHz (around 10us.)
- Sub 0.4 millisecond latency from analogue inputs on stage, through either the CDC eight or CDC six and all the console’s processing, to analogue outputs on stage
- Uses robust RG-6 co-axial cable
- Cable runs of up to 150 meters / 492 feet
- Via the CDC MC Optical bridge runs can be up to 2 km / 6,561 feet on single mode fibre