Orban OPTIMOD-FM 8700, Operating Manual

Page: 97 / 390

OPTIMOD-FM DIGITAL INSTALLATION
2-35
The selections for each of the two AES outputs are I
NTERNAL
, S
YNC
I
N
,
and
I
NPUT
. I
NPUT
sets a given AES3 output sample rate and synchronization to
the same sample rate present at the 8700i’s AES3 (audio) input. Likewise,
S
YNC
I
N
uses the AES11 sync input’s sample rate and synchronization as
the source. I
NTERNAL
synchronizes the given AES3 output rate to the
8700i’s internal clock and uses the S
AMP
R
ATE
setting to determine its
output sample rate.
For a given AES3 output, the output sample-rate selector (“ S
AMP
R
ATE
”)
has no effect in the I
NPUT
and S
YNC
I
N
modes unless sync is lost. Then the
output reverts to internal sync at the sample rate that is preset by the
sample-rate selector for that output. Otherwise, the output sample rate
follows the sample rate present at the selected input regardless of the
setting of the output sample rate selector.
If no signal is provided to the 8700i digital input or S
YNC
I
N
, set SR S
YNC
to I
NTERNAL
and select the desired output sample rate.
There is a sync reference input (labeled Ref In) on a female BNC jack on
the rear panel. It accepts a 1x 5V p-p squarewave wordclock signal at 32,
44.1, 48, 88.2, or 96 kHz, or a 10 MHz sinewave or squarewave signal, 0.5
to 5 V peak. 10 MHz is a common output frequency produced by GPS and
rubidium frequency standards. You can configure the 8700i to lock its 19
kHz pilot tone and output sample frequency to this input.
When a valid reference signal is applied to this input, it locks the Opti-
mod’s Internal DSP clock to this input, so if a given AES3 L/R output’s sync
source is set to Internal, the sample frequency at that output will be
locked to this reference signal. This will also lock the 192 kHz sample rate
of the digital composite output and the pilot tone frequency appearing
at both the analog and digital composite outputs to the reference signal.
See Digital Composite Outputs on p. 2-11, Digitized Subcarrier Inputs on
p. 2-11, and Wordclock/10 MHz Sync Reference Input on p. 2-11
H) Set the desired output W
RD
L
ENGTH
(word length).
[14], [16], [18], [20], or [24] bits
The largest valid word length in the 8700i is 24 bits. The 8700i can also
truncate its output word length to 20, 18, 16 or 14 bits. The 8700i can al-
so add dither and you should set it to do so if the input material is insuf-
ficiently dithered for these lower word lengths. (See the next step.)
I) Adjust
D
ITHER
to
I
N
or
O
UT
, as desired.
[In] or [Out]
It is wise to leave this control set to
I
N
.
When set to
I
N
, the 8700i adds “high-pass” dither before any truncation
of the output word. The amount of dither automatically tracks the set-
ting of the
W
ORD
L
ENGTH
control. This is first-order noise-shaped dither
that reduces added noise in the midrange considerably by comparison to
white PDF dither. However, unlike extreme noise shaping, it adds a max-
imum of 3 dB of excess total noise power when compared to white PDF