Chapter 15:
Test/Alignment Procedures - Audio
Bypass Relays
The two AES/EBU channels must be tested independently. To test Channel 1, set the
channel 2 input source to “Test Tones”. Connect the analog audio outputs from
channel 1 to the Audio Precision test set. Connect the Audio Precision monitor
outputs to the oscilloscope. With the AES/EBU inputs in the “process” position, the
two sine waves should be observed on the scope. Change the channel 1 AES/EBU
inputs to “bypass”, and the sine waves should disappear. Changing back to “process”
should restore the sine waves.
Change the global AES/EBU input source to XLR and repeat the previous tests.
Repeat the above tests with the remaining Channel 2.
AES/EBU output modes
Connect the two AES/EBU BNC output signals to the oscilloscope. When 96kHz
AES output mode is disabled, the eye frequency of both signals should be 6.144MHz.
When 96kHz AES output mode is enabled, the eye frequency should double to
12.288MHz. Restore the 96kHz Output mode to the “disable” state.
When the AES Electrical level is set to “AES”, the signal voltage should be
1Vpp+/-0.1V, not counting overshoot. When the level is set to “SPDIF”, the signal
voltage should be 0.5Vpp+/-0.1V, not counting overshoot.
SDI Embedding and DigiDuplex
Put the DPS-475 test bench unit in DigiDuplex mode. The SDI output should be
looped back to the SDI input. The de-tuned reference composite video source is
applied to the composite input of the DPS-475. The audio DigiDuplex output should
be selected as SDI. Connect the oscilloscope to the audio precision monitor outputs.
With the Audio Precision generators active, the scope should indicate valid tones.
Auto-Track
Connect one of the scope probes to BTP1 and the other to BTP2. Apply the de-tuned
reference composite video source to the composite input of the DPS-475. Select the
video source as COMP. With Auto-Track disabled, the two waveforms displayed on
the scope will be stable with respect to each other. With Auto-Track enabled, then one
of the traces should jump periodically, compared to the other trace. Disabling Auto-
Track should restore the two traces to stability.
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