— 12 —
shield grounds and the AC power cord ground. A ‘ground-
lifting’ AC adapter may well remedy such a situation, although
the chassis must somehow be returned to earth ground for
safety. Generally, being screwed-down in the equipment rack
will satisfy the safety requirement.
PROGRAM LINE INPUTS
AES Digital
Input
The female XLR connector labeled
AES DIGITAL INPUT
is a bal-
anced, transformer-coupled digital stereo program input con-
forming to the AES3 (AES/EBU) specification. This input ac-
cepts digital audio signals up to 24 bits in word length, and at
sampling rates of 32kHz, 44.1kHz, 48kHz and 96kHz. The on-
board sampling rate converter (SRC) locks onto the input signal
automatically and gives a display of the data rate in the
Setup /
Sample Rate Converter
menu (Page 39).
The digital input will accept average program levels between
–5dBFS and –35dBFS, presupposing a nominal, “zero-VU” aver-
age level close to –20dBFS. Gain is programmed under the
Set-
up / Audio Input / Digital Gain
menu (Page 19).
Analog
Line Inputs
The DAVID IV has electronically-balanced (transformerless) left-
and right-channel
ANALOG INPUTS
with female XLR connectors.
These are bridging, high-impedance inputs. They do not pro-
vide termination for the console or other equipment that feeds
the DAVID IV. Here’s why.
With few exceptions, audio line impedance matching is ridi-
culed by today’s hip broadcasters (you) and erudite equipment
manufacturers (us). The concept of 600-ohm “line matching”
dates from the age of transformer-coupled telephone transmis-
sion lines and the necessity of optimizing telephony ‘return
loss’ performance.
The analog line inputs accept “zero-VU” program levels be-
tween –15dBu and +15dBu. The input gain is adjusted under
the
Setup / Audio Input / Analog Gain
menu (Page 19).
Unbalanced
Operation
It’s not uncommon for “Part 15” as well as blatant pirate
broadcasters to include consumer audio products in their in-
stallations. Also, there may be a legitimate reason to feed the
DAVID IV directly from a CD or MP3 player or a computer
sound card in a ‘professional emergency’. Sufficient gain has
been included to interface with single-ended inputs in the
–10dBv, consumer-level range.
For unbalanced inputs, the single center conductor of the
shielded lead should be connected to Pin 2 of the XLR plug, and
the shield braid split and connected both to Pin 1 and to Pin 3.
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