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SR1 Operation 79
© 2014 Stanford Research Systems
2.3.4 Digital I/O Panel
SR1's digital audio inputs and outputs work with both the AES/EBU and S/PDIF standards for digital
audio over a wide range of sampling rates from 24 kHz to 216 kHZ. SR1 also makes a variety of digital
audio carrier measurements including carrier amplitude, sampling freqency, and output-input delay.
Finally, to test susceptibility of devices to carrier degradation SR1 provides number of different types of
carrier impairments including jitter, common and normal mode interference, and variable rise times. All
these functions are controlled from the three tabs of the Digital I/O panel.
Output Configuration Controls
Select the output source as either BNC (Unbalanced) or XLR (balanced). Although the digital audio
signal is always output to both connectors, the displayed amplitude is only calibrated for chosen
connector. Amplitude ranges from 2 mVpp to 2.55 Vpp can be selected for the BNC outputs while
amplitudes from 10 mVpp to 10.2 Vpp are available for the XLR outputs. Output amplitudes are
calibrated only when the outputs are correctly terminated, i.e. 75 for unbalanced outputs and 110 for
balanced outputs.
Selecting Dual-Connector sets the digital audio output to dual-connector mode. In normal digital audio
data streams each frame contains a pair of samples, one left and one right. In dual-connector mode
each data stream outputs a set of successive samples for a single channel with an effective single
channel sampling rate of twice the frame rate. In dual-connector mode the left channel is output on C1
and the right channel on C2.
The Optical indicator indicates whether the TOSLINK (Optical) output is active. The indicator glows
green to indicate that the optical output is active and red to indicate that optical
output may not work correctly.
FS Invert controls the polarity of the of the rear-panel Frame Sync signal. This signal is normally high
during the first (left) subframe of each digital audio frame. Checking the box inverts this polarity.