360 Systems 2470SD Time Delay - Manual (Page 35)

Maintenance 35
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
procedure 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 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 a digital output.
2. Set the delay time to a minimum value, so that an input signal will appear at the Main
Outputs.
3. Use the audio generator to apply a 1 kHz sine wave at a level of +4 dBu to analog audio
Input 1-L.
4. While observing the digital output level of audio Channel 1-L, adjust input gain trim pot RV2
until a level of –20 dBFS is obtained. (+4 dBu is 20 dB below full scale, which is +24 dBu;
therefore it reads 20 dB below full scale or Fs.)
5. Repeat steps 2 through 4 for analog audio Input 1-R, while adjusting input gain trim pot RV1.
The server’s input gain is now calibrated. It remains to calibrate each analog output for unity gain
using the following procedure:
6. Position all audio output jumper blocks to obtain analog outputs.
7. Apply a 1 kHz sine wave at a level of +4 dBu to analog audio Input 1-L.
8. While observing the output level of audio Channel 1-L, adjust output gain trim pot RV4 until a
level of +4 dBu is obtained.
9. While observing the output level of audio Channel 1-R, adjust output gain trim pot RV3 until a
level of +4 dBu is obtained.
10. Repeat steps 9 and 10 to adjust the gain of the left and right outputs.
The server’s output gain is now calibrated, and the entire sequence of the preceding steps has
established a gain of unity through the server. Another method is to use digital input with a digital sine
wave of –20 dBFS to calibrate analog outputs 1 & 2.