10
TH2/AM8 SYSTEM SETUP PROCEDURE
When used in conjunction with one or more AM8’s, the following procedure will insure optimum operation. The
system architecture provides for algorithm-controlled gain paths that require the signal levels received by the TH2 and
the signal levels within the AM8 (microphone or other line level devices) be relatively equal. When this is achieved, a
very high quality teleconference results with seamless, near-duplex operation.
The following procedure will serve as a guide to balancing TRANSMIT (near end signal from the AM8) and RECEIVE
(far end signal received by the TH2) signal levels without the need for any external test equipment or computer:
1) Set the inputs of the AM8 for proper gain.
The first step is to select the appropriate mic preamp gain on the AM8. Most condenser and some wireless mics
would use +30dB gain setting, while most dynamic mics or if the mic to talker distance is great would use +50dB
gain setting; 0dB gain setting is used for devices capable of producing line level output signals (tape deck, CD
player, some wireless mics).
2) Adjust the individual CHANNEL LEVEL and MAIN LEVEL controls.
Start with the CHANNEL LEVEL and MAIN LEVEL controls on the AM8 at mid position and have someone talk
into one of the mics at a normal operating distance. Switch the COMP/LEVEL to the IN position and set the
THRESHOLD trim pot to “-10.”Now adjust the input channel level control so that only the right-most three LEDs
come on at the loudest peaks in the speakers voice, while during the normal speech no LEDs should be lit. The
proper adjustment of the COMP/LEVEL would cause compressor/leveler action only during the very loud speech
or if the participant leans very close to the mic.
If local sound reinforcement is not used in the room, turn the MAIN LEVEL to minimum since this pot will not
influence the TRANSMIT signal. If local sound reinforcement is incorporated in the room, adjust the MAIN LEVEL
pot and the volume on the power amplifier (PA) to the desired SPL in the room. Check each AM8 input’s contribu-
tion to the SPL in the room, and re-adjust the CHANNEL LEVEL such that all inputs are approximately at the
same SPL in the room. Note that the MAIN LEVEL and PA volume are essentially connected in series, so that if
you increase one and decrease the other, the SPL in the room should be about the same.
3) Establish an outside call.
The best results are achieved using a Plain Old Telephone System (POTS) line, or using a telephone line simula-
tor such as Teltone TLS-3, or TLS-4. When setting up the TH2, establish a call “off-site”and adjust for the average
of several calls since there might be some difference in received levels from one call to another. It is best to avoid
calling from an “in-house”extension within the same PBX or KSU, since such a call would typically be 6-10dB
louder than an outside call. Furthermore, initially avoid test calls from the bridging service since they are typically
6-10dB quieter than an outside call.
4) Adjust the RECEIVE LEVEL trim pot.
Starting from the mid position on the RECEIVE LEVEL trim pot on the TH2, adjust the level so that the incoming
call is heard through the local PA system at about the same SPL as the AM8 inputs (mics and line level devices).
If local sound reinforcement is not used, adjust the RECEIVE LEVEL to the desired SPL in the room. In both
cases, the RECEIVE SIG LED will be lit when far-end signal is received through the TH2.
If the RECEIVE LIM LED is lit, you are clipping the signal either at the output, or internally in the Digital Signal
Processor (DSP). Back off on the RECEIVE LEVEL all the way to the minimum - if the LIM LED is not lit, your
RECEIVE LEVEL was too high. If the LIM LED is still lit, your phone line signal is “too hot”, and you need to
switch the RX ATTENUATE dipswitch to -10dB position to prevent DSP internal clipping. After the dipswitch
positioning, adjust the RECEIVE LEVEL to the desired SPL in the room.
