Tempest 900 - Test for Echo

51
Tempest900 2-Channel Operating Manual
Auto-Null Explained
In 2-Wire intercom systems, inefciencies 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 hard
wired 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 hard wired 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 signicantly, such as when additional wired BeltStations are
added or removed, or when cable lengths are changed signicantly.
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 rst enabled, it
requires up to 10 seconds for it to achieve convergence. There will usually be some noticeable echo during the rst 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 efciency.
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.