Clear-Com Tempest900 - Manual (Page 58)

52 Tempest®900 2-Channel Wireless Intercom System
Auto-Null Explained
In 2-Wire intercom systems, inefficiencies in the hybrid circuitries that combine or separate the send and receive audio signals
onto the same pair of wires inherently cause echo. Within analog systems the echo is not noticeable, but when connected to an
extremely sensitive digital system, the echo becomes more problematic.
In order to minimize echo resulting from connection to an external 2-Wire system, it is necessary to optimize the hardware of the
hybrid circuitry in the Tempest BaseStation. Tempest provides a user initiated AUTO-NULL feature that automatically optimizes
the 2-Wire interface. Nulling only impacts 2-Wire hardwired intercom connections.
Auto-Null sends a tone to each of the 2-Wire intercom channel connections. The Tempest Wireless BaseStation DSP monitors the
echo and adjusts the line characteristics (Resistance and Capacitance) to optimize the interface to the external 2-Wire system.
When Auto-Null is initiated, all of the functions of the BaseStation including communication are interrupted. The Auto-Null
process takes approximately 10 seconds. Intercom levels may need to be adjusted after the 2-Wire intercom lines have been
nulled.
Auto-Null Procedure
Turn OFF all TALK buttons on both the wired and wireless systems. Since Tempest monitors a self generated tone to adjust
the null characteristics, any sounds entering through either the wired or wireless intercom systems will interfere with the
nulling process. When the Auto-Null or Manual Null menu screens are accessed, Tempest sends a Mic Kill signal to all
wireless BeltStations, but the wired communication stations will need to be turned OFF individually, or a hardwired Mic
Kill signal will need to be initiated.
On the Tempest BaseStation press MENU to open the Main Menu. Rotate the Volume Control to scroll through the menu
options to the “Wired Intercom Settings” and select “Auto-Null.” Select “Null Now” to start the Auto-Null process. Normal
functions will be interrupted for about 10 seconds during the Auto-Null process. Progress of the null process can be
observed on the BaseStation LCD display.
The BaseStation display will indicate “Auto-Null Complete” once the Auto-Null process is completed. Press MENU to escape
to the Operational screen.
Activate Auto-Null for new connections or whenever the 2-Wire system changes significantly, such as when additional
wired belt packs are added or removed, or when cable lengths are changed significantly.
Test for Echo
Talk into the wireless system for at least 10 seconds to test for echo. Echo Cancellation (ECAN) software is disabled in the
Auto-Null and Manual Null screens to ensure the best hardware null. Press MENU to exit the nulling menu screen, and to
enable ECAN. When ECAN is first enabled, it requires up to 10 seconds for it to achieve convergence. There will usually be
some noticeable echo during the first few seconds of testing, but it will diminish over time as the ECAN software converges
to an inaudible level. Brief louder active audio can help accelerate efficiency.
During Auto-Null, wired intercom users will hear the nulling tones and communication will
be interrupted. It is recommended that this feature should be used only during setup and
not during live events.
If multiple BaseStations are connected by 2-Wire intercom connections, each BaseStation
must be nulled separately. Null one BaseStation at a time.