BLU Link Overview

BLU link is an audio bus found on all of the BSS London BLU devices as well as other HARMAN devices. It carries 256 channels of audio at 48kHz, and 128 channels at 96kHz, both at 24bit (note that BLU-100, BLU-101 and BLU-102 are restricted to 48 channels at 48kHz). When connected in a loop, it has redundancy, allowing any one BLU link cable to break while still maintaining audio.

 

 

Hardware Configuration

On the rear of the BLU link devices there are two BLU link ports. One is the BLU link In, and the other BLU link Out. Devices are connected together by wiring Out to In on all of the devices within your BLU link network, making sure that the loop is complete so that there are no empty BLU link ports.


You should not connect the BLU link ports to anything other than BLU link ports. BLU link will not function if you try to connect the BLU link to an Ethernet switch for example.

 

Fault Tolerance

The network is capable of a degree of fault tolerance due to the fact that each device receives the same audio from 2 other devices. If a cable is broken the devices which are no longer connected will detect the cable break. One device will detect that its 'In' port is unconnected and the other will detect that its 'Out' port is undetected.

In the diagram above, if there was a break in the cable between U3 and U1, U1 will detect that its 'In' port is no longer connected. Therefore the audio it sends to the DSPs must now come from its 'Out' port. In addition, its default behavior of passing audio from 'In' to 'Out' and vice versa is no longer applicable. Instead it must route incoming audio from its 'Out' port back out of the same port.

U3 will detect that its 'Out' port is no longer connected. Since its default behavior is to receive audio from its 'In' port, it can continue doing that. However, its default behavior of passing audio from 'In' to 'Out' and vice versa is no longer applicable. Instead it must route incoming audio from its 'In' back out of the same port.

The two devices in the middle of the ring do not know that the ring has been broken and continue to forward audio between their 'In' and 'Out' ports. They will also continue to take their audio from their 'In' port to send to the DSPs.

In this broken network a signal transmitted by U3 will travel back along the ring until it reaches U1. There the audio does a U-turn and heads around the ring the other way and is then received by all the devices on the network since it will be present at their 'In' port inputs.

Note that when the cable is broken, the audio takes longer to reach its destination than before. This added delay is not compensated for in any way, but is a side-effect of the way the fault tolerance works.

 

Mastership

The BLU link network requires one device on the ring to act as master for the whole ring. The master will provide the clock for all the other devices on the ring. This means that the whole ring is synchronized to a single audio clock.

If a device has a CM1 card installed i.e. BLU-800 or BLU-320, and the device is connected to a valid CobraNet network, then that device will receive its clock from the CM1 card by default. Therefore, if you connect a BLU-800 or BLU-320 to a CobraNet network, you must ensure that devices on a particular BLU link ring are only connected to a single CobraNet network.

If a device has an AVBX card installed, and that device is connected to a valid AVB network, then that device will receive its clock from the AVB card by default. Therefore, if you connect this device to an AVB network, you must ensure that devices on a particular BLU link ring are only connected to a single AVB network.

If a device has a DANTE card installed i.e. a BLU-806DA, BLU-326DA or a BLU-DA, and that device is connected to a valid DANTE network, then that device will receive its clock from the DANTE card by default. Therefore, if you connect a BLU-806DA, BLU-326DA or a BLU-DA to a DANTE network, you must ensure that devices on a particular BLU link ring are only connected to a single DANTE network.

 

It is not possible to connect multiple devices on one BLU link ring to different CobraNet or to different AVB or DANTE networks. Neither is it possible to connect multiple devices to a mix of Cobranet and AVB networks. This is because each CobraNet or AVB network will have a conductor to provide the clock. The BLU link ring would then have multiple clocks present on one network, and this is not permitted.

 

If a BLU-800, BLU-320, BLU-806DA, BLU-326DA or a BLU-DA is set in properties to Sync to BNC then that device will take its clock from the BNC input on its rear panel. Priority for these units should be set higher than other units to ensure the BLU link master is a unit with a BNC connection. Audio Architect will warn of errors in priority settings before going online. In this case it is recommended that the CobraNet or AVB network should not be used since CobraNet / AVB audio will be compromised as it is synchronising from a different clock source. The DANTE network can be used as the DANTE card will sync from an external clock.

 

Mastership is negotiated between all the devices on the ring, and a change to the ring will trigger the negotiation to be started. There are various rules for determining which device on the ring becomes clock master :

BLU-link LED indicators

These are found on the Blu link ports on the back panel of the device and indicate the following:

The green LED will indicate a link on that particular port

Both on: The box is the master. (No green LEDs will be on if no cables are connected).

Only one on: The box is locked to the data coming in on that particular port

Both off: The box is locked to CobraNet


Control Panel

 

The default control panel is accessed by right clicking on the device in the Main Window and selecting 'Show Default Control Panel'. The default control panel for a BLU-800 is shown below.

 

 

 

Software Configuration

The BLU link devices placed in the Venue show the BLU link In and Out ports which allow you to wire the devices together, as shown in the diagram above. Note: It is not necessary to wire the BLU link ports together within HiQnet Audio Architect in order for BLU link to function.


Editing BLU Link Bus

Multiple BLU link networks may exist within an Audio Architect design file. By default, each device belongs to BLU Link Bus 1. Every BLU link device must be part of one BLU Link Bus. The device properties show which BLU link network the device is part of. Click on the ... icon in the Properties window to edit.

 

This property can be edited to add, delete, edit the name of, and assign the device to a BLU Link Bus. The diagram above shows that four BLU link networks exist in this design file, and that the device belongs to BLU link 1 which is shown highlighted.

 


 Configuring a BLU Link Device

In the Processing Objects > BLU Link menu you will find the BLU link Input/Rx and BLU link Output/Tx processing objects. Initially they have no nodes on them.

You can add and remove as many BLU link processing objects as you wish inside a BLU-800 and BLU-160. The BLU-320 by default contains 2 BLU link Inputs and 2 BLU link Outputs and the BLU-120, BLU-100 by default contain 1 BLU link Input and 1 BLU link Output. You cannot add or delete BLU link processing objects in the BLU-320 or BLU-120.

 

Each BLU link processing object supports a maximum of 32 channels. To assign channels to the BLU Link Input and/or Output module, click the "CH" box in the module. This will bring up a window:

 

See BLU-Link Input Channel Assignment information HERE

See BLU-Link Output Channel Assignment information HERE

 

BLU link Specification