CobraNet

CobraNet is a widely adopted audio network solution. Audio Architect has been created to maximise the inclusion of CobraNet devices, including Crown and other manufacturers, in a single system design. Peak Audio's CM-1 module has been used within the BLU series processors to interface with the hardware.

Channel Count

As standard, devices within the Soundweb London system are capable of transmitting and receiving a maximum of 32 channels of CobraNet audio onto and from the network. This channel count may be reduced if higher sample rates or lower latencies are required - see Table C. Each BLU-80 and BLU-32 Soundweb London device may transmit and receive four CobraNet bundles which can carry a maximum of 8 audio channels at the default setting of 48 kHz, 20 bit.

Bundles

Each output bundle may be assigned to be Unicast or Multicast. A Unicast bundle may have only a single receiving device and will not be transmitted unless the receiving device is requesting, enabling destination controlled routing. A Multicast bundle may have multiple receiving devices. No more than three Multicast bundles should exist within the network to maintain a sensible level of network traffic.

Sample Rate and Bit Depth

To maximise channel count, the CobraNet network should be configured to operate at 48kHz. Each bundle can carry 8 channels of audio data at 16 or 20 bit. A maximum of 7 channels will be available if all channels within a bundle are required to be 24 bit.

The CobraNet network can also be configured to operate at 96kHz. It is recommended that CobraNet is not used on a system where a device in the design has it's clock synchronized to BNC since the CobraNet clock will not be synchronized to the word clock and this will compromise the CobraNet audio.

Latency

Delay is incurred by the buffering of audio data into Ethernet packets in CobraNet transmitters and receivers. Additional delay is incurred in analog to digital conversion, digital to analog conversion and sample rate conversion. These additional delays are usually only in the order of dozens of samples and of no consequence. Data on an Ethernet network travels at the speed of light, and for long distance runs optical fire connections should be used. Standard fast Ethernet runs over CAT-5 copper cable should be up to 100m.

The maximum latency incurred in a CobraNet network is 256 samples (5-1/3ms) per switch or device through which the audio data must pass. This latency can be reduced at the expense of CobraNet audio channels transmittable from device to device and all devices on the network must be configured to operate at this latency.

A CobraNet network utilising the CM-1 module can make use of a number of possible latency times and sample rates.

Latency against sample rate at 20-bit resolution:

Clock

The CM-1 modules within the devices on the network automatically negotiate a 'conductor' that generates a master clock for the network. An LED on the front panel of the BLU-80 and BLU-32 indicates which device contains the conductor. If the conductor device should fail then the network will assign the conductor status to another device, this process takes milliseconds, although audio cannot be passed through a CobraNet network without a conductor.

Network

The Soundweb London system requires an Ethernet LAN backbone for both proprietary system communications/control and CobraNet audio distribution. Consequently each Soundweb London processor requires a total of two network ports for CobraNet audio and one for control. CAT-5 cable should be employed for connectivity. It is recommended that the network should be a discrete system for audio and communications and should not be used for any other network purposes. Crown Audio amplifiers and other CobraNet devices may be connected.

CobraNet does not use TCPIP and should happily coexist on a network running this protocol. CobraNet does not run successfully over current wireless networks due to their inability to guarantee real time transmission (as needed for audio)

Switches & Hubs

Ethernet repeater hubs are not recommended and may not be connected into a switched CobraNet network. A network may consist only of all switches or all repeaters. The Hewlett Packard ProCurve is the Harman Group recommended range of Ethernet switches, for more recommendations check the Peak website. CobraNet currently runs the system at 100BT speed but a gigabit backbone is recommended, particularly in shared usage systems (although it is recommended to have a separate network for CobraNet to avoid collisions and data queuing).

Switch 'hops'

Where possible, the CobraNet network should not include more than seven switch hops (seven switches between transmitting and receiving Soundweb London devices). An additional 256 sample latency will be induced for each subsequent switch hop. To combat this, a gigabit Ethernet backbone should be employed which will increase the number of switch hops before additional latency occurs.

CM-1 RJ45 LED Flash Codes

Each CM-1 card has two RJ45 network ports labled Primary and Secondary. These ports each have two LED indicators that will flash to indicate the status of the port. Here are the flash codes for these ports:

Redundancy

The CobraNet compatible devices within the Soundweb London system are fitted with a Peak Audio/Cirrus Logic CobraNet CM-1 module. The module itself offers a Primary and a Secondary CobraNet port. Under normal operation the Primary port only receives audio data from and transmits audio data to the network. Should the Primary port or connection fail, the CM-1 module automatically switches to receive from and transmit with the Secondary port. This must be considered in network design. It may be appropriate to connect the Primary CobraNet port to a Primary network and the Secondary CobraNet port to a Secondary, backup network. In this event, it should be noted that the backup network should in some way be bridged to the Primary network in order for the audio data to be present on the Secondary network should the module switch over.

Communications

Third party controllers may be connected into the system via the serial port using the raw message protocol.

Video

CobraNet, at the time of writing, is not yet capable of delivering video, although this functionality is being developed.

CM1 DSP

The CM1 CobraNet interface card has onboard DSP used to perform various functions. CobraNet latency, bit depth, sample rate and total number of audio channels transmitted or received can increase the CM1 DSP usage. When trouble shooting CobraNet problems, make sure you are not exceeding 100% usage on the CM1 DSP meter. This meter can be found in the Default Control Panel for each London CobraNet device (BLU-80, BLU-32, BLU-800 & BLU320).

CM1 Meters

To conserve valuable DSP resources on the CM1 card, the CobraNet meters on the transmit and receive bundles are turned off by default. These can be turned on to aid in trouble shooting CobraNet, but should not be left on unless the DSP usage on the CM1 can support the current design without exceeding 100% usage.

To turn the CM1 meters on:

1. In Design Mode, highlight the London CobraNet device in the Main Layout Window.

2. Open the Properties Window.

3. Expand the Parameters section.

4. Change the value of CobraNet Meters to ON.

5. Go Online with the system.

6. Choose Send Values to Network Device from the Parameter Synchronization dialog.