CobraNet technical overview
Component Overview
Here are a some important concepts to help you understand the capabilities of a MediaMatrix CobraNet system.
A CobraNet data bundle that contains a number of audio channels, typically 8. A CobraNet bundle number is a unique identifier for that bundle.
The user is free to assign CobraNet bundles as they desire. There are a few general rules however, that must be heeded. First, only a single transmitter device should be assigned to any bundle. If more than one transmitter is assigned to a bundle, only the first transmitter assigned that bundle will be allowed to transmit. Also, be aware that CobraNet bundles do not need to be assigned sequentially.
|
Bundle Number |
Designation |
Description |
|
Off |
Null |
Disable transmission Never transmitted |
|
1 - 255 |
Always transmitted with well known broadcast addresses. | |
|
256 and greater |
Unicast or broadcast with well known address dependent on reverse reservations. |
Broadcast bundles are a global resource. There may be only one transmitter assigned to a broadcast bundle during any isochronous cycle. This restriction is enforced by the conductor. Broadcast bundles represent a least common denominator for audio interoperability in networks configured via front panel selections. Since these bundles are always broadcast, no reverse reservation is required to receive them. Since they are never unicast, Broadcast bundles can wreak havoc on switched networks. In MediaMatrix CobraNet equipment, broadcast bundles are those whose Bundle number is anything from 1 to 255.
Public bundles are a global resource. There may be only one transmitter assigned to a public bundle during any isochronous cycle. This restriction is enforced by the conductor. These bundles may be unicast or broadcast at the discretion of the transmitter based on reception of reverse reservation requests. In most cases, we refer to these as "Unicast Bundles," though, in reality, that's only because we typically only assign one receiver to these bundles. It is unicast in this circumstance, but you are not limited to unicasting with public bundles. In cases where one transmitter must transmit to multiple CobraNet devices without using pure multicasting, the reverse reservation of unicast addressing sets up one-to-many transmission, while also not broadcasting to all network ports. In MediaMatrix CobraNet equipment, public bundles can be selected by choosing bundle numbers from 256 to 32767.
Tip: When using Public or Unicast Bundles, you may find it easier to start your bundle assignments at 1001, rather than 256, to better match the hardware ID's of the CABs.
Each CobraNet Transmitter can send on one Network Bundle. Each CobraNet device may have one or more Transmitters. A Transmitter is a "virtual" device, residing in the software embedded in a hardware CobraNet node.
Each CobraNet Receiver can receive from one Network Bundle. Each CobraNet device may have one or more Receivers. A Receiver is a "virtual" device, residing in the software embedded in a hardware CobraNet node.
A CobraNet network is synchronized to the sample clock of a CobraNode on the network designated the conductor. The conductor of a CobraNet network is chosen through an arbitration procedure. A conductor priority is instrumental in determining which unit serves as the conductor of a CobraNet network. The unit with the highest conductor priority will serve as the conductor. If two or more units share the highest conductor priority, the first unit to connect to the network becomes the conductor.
All other nodes on the network receive their sample clock over the network. Each CobraNet device has an electronically adjustable oscillator that allows each node to synchronize to the conductor.
CobraNet BoB Input
Technically, a CAB™ 8i or CAB™ 16i - AUDIO BRIDGE. The CAB™ 8i is a 1 rack-unit device has 8 analog switchable mic or line-level audio inputs and a variety of control inputs and outputs. The CAB™ 16i is a 1 rack-unit device has 16 analog audio inputs. Also the CAB™ 16d can receive 16 audio channels of digital audio from AES3 or S/PDIF sources. They are also referred to as Input CABs in this document. It attaches to a MediaMatrix Mainframe via a CobraNet network. An Input CAB supports 4 CobraNet Transmitters.
CobraNet BoB Output
Technically, a CAB™ 8o or CAB™ 16o - AUDIO BRIDGE. The CAB 8o device has 8 analog line-level audio outputs and a variety of control inputs and outputs. The CAB™ 16o is a 1 rack-unit device has 16 analog line-level audio outputs. Also the CAB™ 16d can transmit 16 audio channels of digital audio to AES3 or S/PDIF compatible equipment. They are also referred to as an Output CAB in this document. It attaches to a MediaMatrix Mainframe via a CobraNet network. An Output CAB supports 4 CobraNet Receivers.
CobraNet Interface Card
The hardware interface card that attaches to a MediaMatrix DSP card, enabling the DSP card to control and configure a CobraNet network and to send and receive CobraNet audio. It can send 32 audio channels from the DSP card and receive 32 audio channels into the DSP card. It supports 4 CobraNet Transmitters and 4 CobraNet Receivers.
NOTE: Each DSP card can have a single I/O daughter interface attached, and there are different interface cards to support Local BoBs, AES-3 digital audio and CobraNet.
Local BoBs
Technically, an MM88xx or MM8802. These are the classic MediaMatrix audio I/O devices, each having 8 analog audio inputs, 8 analog audio outputs and a variety of control inputs and outputs. Local BoBs attach to a MediaMatrix system with a short point-to-point cable (MM-88xx/MM-8802) or two runs of up to 50' of CAT5 cable (MM-8802).
CobraNet Limits in version 3.x
In order to make CobraNet easier to use while still accommodating the requirements of most applications, we have set some limits as to the configuration potential of the Interface Card and the CABs in MM 3.x. This includes the following:
Each Network Bundle contains 8 audio channels.
The digital audio resolution is 20 bits (but can be changed to 18 or 24bits (sacrificing 1 channel per bundle).
An Interface Card has 4 Transmitters and 4 Receivers.
An Interface Card's 4 Transmitters map directly to its DSP card's 4 Audio Port Outputs, and the 4 Receivers map directly to the 4 Audio Input Ports.
Of these limitations, only the Interface Card Transmitter and Receiver count is fixed by software. The others can easily be overcome with the addition of some View File devices and technical support.
Hardware
To utilize CobraNet in MediaMatrix, the following hardware is needed:
1 or more CobraNet Interface card for MediaMatrix
1 or more CAB
Standard Ethernet switch (not a hub) and CAT5 (EIA/TIA 468A/B) cables
Each CobraNet network consists of a single CobraNet interface and some number of input and output CABs connected to the same Ethernet switch. All audio transmitted on that network is available to any other CobraNet device on that network. To route audio from one network to another, the routing must take place inside the MediaMatrix frame.
It is recommended that each CobraNet Interface Card and the set of CABs that are to provide audio I/O for a DSP card be connected to its own network. It is also recommended that other Ethernet devices, such as PCs and network printers not be attached to a CobraNet network since the traffic they generate can cause dropouts in the CobraNet audio. If you absolutely have to mix network traffic, please consult the CobraNet web-site for tips and complete rules.
Software
The CobraNet Interface card and the CABs are configured with devices placed in the MediaMatrix view file, and the presence of these devices is required in order to initialize the hardware.
CobraNet Interface Card
The number on the face of the Interface Device corresponds to the DSP card it is connected to. The Interface Card device allows for monitoring the status LEDs, assigning Network Bundles and setting the audio resolution of the Transmitters. The Transmitting LEDs indicate whether the Interface Card has been allowed to transmit on the requested bundle, and the Receiving LEDs indicate if valid audio data is being received on the specified bundle.
CAB 8i CobraNet Input BoB
The number on the face of the Input device needs to match the CAB ID. The device allows for specifying the Network Bundle it transmits on, as well as various analog input settings such as the gain, mic/level line selector, mute, and phantom power.
CAB 16i CobraNet Input BoB
The number on the face of the Input device needs to match the CAB ID. The device allows for specifying the two Network Bundles it transmits on (for a total of 16 audio channels), as well as various analog input settings such as the gain, and mute.
CAB 8o CobraNet Output BoB
The number on the face of the output device needs to match the CAB ID. The device allows for specifying the Network Bundle it receives from, as well as various analog input settings such as the gain and mute.
CAB 16o CobraNet Output BoB
The number on the face of the output device needs to match the CAB ID. The device allows for specifying the two Network Bundles it receives from, as well as various analog input settings such as the gain and mute.
CAB 16d Digital Input/Output BoB
The number on the face of the output device needs to match the CAB ID. The device allows for specifying the two Network Bundles it receives from and the two Network Bundles it transmits to. There are no controls for input level or mute, because the input level is determined by the device sending the digital audio to the CAB 16d. There are also no controls for output level because the output should always be at 0dB. You can still set the CobraNet audio level being transmitted or being received in the CobraNet audio blocks.