Ericsson EDACS LBI-39077 - Manual (Page 57)

BALANCE AND LEVEL LBI-39077
57
ADJUSTING AUDIO LEVEL FROM PHONE
When configured for 2-Wire telephone lines (DID and End-to-End) all hardware gains in the GTI are set to predetermined
values, so level adjustments in the conventional sense, do not exist. However, as there are significant differences in phone
lines, the GTI does have a way to compensate for these variances (using DSP).
The Audio From Phone controls the software gain of the GTI for audio from the phone line to the radio. The GTI defaults to a
gain for an average phone line and the Audio from Ph. adjustment raises or lowers the audio gain in 3 dB steps. This is a
subjective adjustment and should only be adjusted if overall caller voice levels are perceived to be soft (or loud). It should be
noted that if this adjustment is too high, background noise from the radio may become excessive.
Move the highlighted cursor to a desired line and press the Enter key to see available selections on the pop-up window. To
adjust the Audio Level from Phone, choose the 'Audio from Ph.' menu item. You may select this item for any line type at any
time, even in the middle of a call.
A bar graph will appear with the current level setting in the GTI unit. To adjust the levels, use the arrow keys to move the
settings bar graph up and down. Once the desired level has been set, wait one second for the new level to be registered by the
GTI Configurator. The GTI Configurator will send the new level to the GTI unit and receive a confirmation that the level was
set. In the intervening time the bar graph will dim until it receives the confirmation.
Press the Enter key to finish the adjustment and return to the menu. If you press the Enter key before the one second delay
time, any new setting will not be sent.
OVERVIEW OF 4-WIRE LEVELS
Audio levels used in 2-Wire phone systems are well documented and standardized. As noted previously, the only level setting
required for 2-Wire lines is software gains in the DSP. On the other hand, 4-Wire lines do not have this standardization.
Therefore, when working with 4-Wire lines, in addition to the software gains used for 2-Wire lines the GTI has hardware
gains that must be adjusted to support each individual system.
There are two types of 4-Wire circuits the GTI will operate with. The most obvious type of circuit are lines that terminate to a
4-Wire service (such as Type 1 E&M lines). The second type of 4-Wire circuit are those that ultimately terminate to a 2-Wire
service (typically End-To-End or DID lines extended via a microwave system).
When connected to 4-Wire lines (that ultimately terminate 4-Wire) the GTI hardware gains need to be set to ensure proper
test tone levels to the phone network. For setting gain towards the phone network, this is done by having the GTI generate a
tone and measuring the level at the phone interface while the adjusting the gain. Setting the gain from the phone network is
done by calling milliwatt (or other known signal source), monitoring the received level (through the configurator) and
adjusting the gain. Once the hardware gains are set, additional changes to the apparent loudness may be made by varying the
software gains.
If the GTI is connected to a 4-Wire circuit that is derived from a 2-Wire circuit (such as End-To-End lines extended via
microwave) certain overall relationships must be maintained in order for the GTI to provide maximum sidetone suppression
for the radios using the system.
The following 4-Wire level setting procedures have been divided into two sections, the first for 4-Wire circuits that terminate
in a 4-Wire telephone switch and the second for 4-Wire circuits that terminate in a 2-Wire circuit. Be sure to use the correct
procedure.
TERMINATION INTO 4-WIRE CIRCUITS
Adjusting E&M 4-Wire Hardware Gain to Phone
This adjustment sets the to-phone hardware gain for E&M 4-wire lines. An appropriate measurement apparatus is required to
measure the audio tone level traveling from the GTI unit through the E&M lines at the receiving phone side.
Move the highlighted cursor to a 'FREE' E&M 4-wire line and press 'ENTER' to see available selections on the pop-up
window. To adjust the gain, you must first enter a number which has the test equipment connected to it. This number is
entered under 'Silence Setup' or in the database. This is done out of convenience and is not the actual silence number.