Omnia.11 Input Failover / Comparative Fail
Scope
This document covers how to set the "Comparative Fail" control in the Omnia.11's Input Failover feature.
Description/Question
Q: I am using different audio sources for my Primary and Secondary audio inputs. Primary is the STL , Secondary is a local automation playout at the TX site. Where should Comparative Fail be set for my situation?
Solution
A: If there is different program audio on the secondary input, turn Comparative Fail "OFF". (It only makes sense to compare the two inputs if they are supposed to have the same thing to begin with).
For your reference, here is the full information about the Omnia.11's Input Failover feature (From the user manual Pgs. 27-28):
There are 3 controls for the Input Failover feature, Failover Source, Failover Time and Comparative Fail.
The primary input source is set with the “Input Source” control. This is your main input source.
“Failover Source” selects which audio input: Analog, AES/EBU, Livewire 1 or Livewire 2 will serve as the secondary audio input. Note that the audio input that is selected under Input Source (above) will always be the Primary audio input. A source selected under Failover Source will always be the secondary source.
“Failover Time” is the amount of time that will elapse after the failure of audio on the primary input source before the unit makes the decision to switch to the secondary (failover) input source.
For instance, if Failover Time is set for 5 seconds and the primary audio source fails, 5 seconds later the unit will switch to the secondary audio input if that input is active. If at any time, audio is restored on the primary input (for 1 second, continuously), the unit will switch back to the primary audio input. It will remain with the primary input unless another failure is detected.
The “Comparative Fail” control in the Basic tab of the Input menu is normally set to "ON", but, in some extremely rare cases, this has caused a failover to occur when it should not. In order for this "spurious failover" to occur several things must be true:
1) The valid program audio (which is on the primary input) must have one channel silent (or very quiet) for more than the failover time. This occurs in some songs by The Who (and probably The Beatles).
2) The secondary input must not have the same program as the primary input. It must have some program that has audio on both channels.
So you can see it is a rare case where this will happen, therefore the default is "ON", where it will catch more failure conditions.
The comparative failover function looks at both the primary and secondary inputs simultaneously. If the secondary input looks "better" than the primary (it has both channels while the primary has only one, or it is a lot louder), then it switches to the secondary. The switch when “ON” takes place after the condition of the secondary being better has persisted for more than the failover time.
The “OFF” mode failover mechanism is "absolute failover", where it is just looking at the absolute level of the primary input. This mechanism will not react to the loss of just one channel. There may be cases where single-channel audio for a while is valid, but if the secondary input has both channels driven, it is more likely the valid signal, and the primary is in error.
Recommendation: If you are feeding the same program to both the primary and secondary inputs, leave this set to "ON". If there is a different program on the secondary input, turn it "OFF". (It only makes sense to compare the two inputs if they are supposed to have the same thing to begin with).
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