Maintenance = 107
Audio Level Calibration The input gain and output gain of the analog audio circuits are factory calibrated to a +4 dBu
standard. Each circuit includes a trim pot with a range of approximately ±2.5 dB. The following
procedures may be used to calibrate these for unity gain. Each trim pot is located above the XLR
connector with which it is associated. Refer to the preceding drawing (Figure 27) for the location
of trim pots and jumper blocks referred to in the calibration procedures.
Calibration Procedure
This procedure assumes that the technician is fully familiar with test procedures employing the
Audio Precision® test equipment, or its equivalent.
1. Position the jumper block J5 and J6 for Channel 1 output to obtain an analog output.
2. Play the test clip titled zTONE present on the Image Server disk. This stereo clip is
recorded at a level equivalent to a +4 dBu output level.
3. While observing the output level of audio Channel 1 Left, adjust trimmer RV4 until a level
of exactly +4.00 dBu is obtained.
4. Repeat this procedure for audio Channel 1 Right, while adjusting trimmer RV3, and also for
each subsequent audio channel using its associated trim pot.
Having established accurate gain settings for all analog audio outputs in steps 1 through 3
above, calibrate the Image Server’s input gain as follows:
5. Using the graphic user interface, place server Channel 1 in the E-E mode, so that an input
signal will appear at its output.
6. While observing the output level of audio Channel 1-L, apply a 1 kHz sine wave from the
audio generator to audio Input 1-L.*
7. Adjust input trimmer RV2 until a level of exactly +4.00 dBu is obtained at the output of
Channel 1L.
8. Repeat this procedure for audio Input 1-R, making the gain adjustment with input trimmer
RV1.
The preceding steps establish a gain of unity through the server.
* In the absence of a generator, use the calibrated outputs of Channel 2 playing zTONE to
feed the inputs.