Orban OPTIMOD-FM 8600Si, Operating Manual

Page: 243 / 356

OPTIMOD-FM DIGITAL OPERATION
3-77
A 32 kHz sample rate cannot represent frequencies higher than approxi-
mately 15 kHz. Therefore, setting the sample rate to 32 kHz automati-
cally forces the bandwidth to 15 kHz, regardless of the setting of the
HD
B
ANDWIDTH
control
.
Word Leng (“ Word Length”) sets the word length (in bits) emitted from the digi-
tal-channel output.
The largest valid word length in the 8600Si is 24 bits. The 8600Si can also
truncate its output word length to 20, 18, 16, or 14 bits. The 8600Si can
also add dither, which we recommend.
Dither turns on or off addition of “high-pass” dither before any truncation of the
output wordlength.
The amount of dither automatically tracks the setting of the W
ORD
L
ENGTH
control. This first-order noise shaped dither adds considerably less
noise in the midrange than does white PDF dither. However, unlike ex-
treme noise shaping, first-order noise shaped dither adds a maximum of
3 dB of excess total noise power when compared to white PDF dither. It is
thus a good compromise between white PDF dither and extreme noise
shaping.
In many cases, the source material has already been correctly dithered so
you will not need to add dither and can set this control to
O
UT
. However,
particularly if you use the Noise Reduction feature, the processing can
sometimes attenuate input dither to a point where it is insufficient to
dither the output correctly. In this case, you should add dither within the
8600Si by turning this control on.
Sync determines if the sample rate appearing at the digital-channel output is
synced to the 8600Si’s internal clock, to an AES3 signal appearing at the 8600Si’s
digital input, or to an AES11 signal appearing at the 8600Si’s sync input.
S
YNC can be
set separately for Digital Output 1 and Digital Output 2, allowing them to have dif-
ferent sample rates.
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 8600Si’s AES3 (audio) input. Like-
wise,
S
YNC
I
N
uses the AES11 sync input’s sample rate and synchroniza-
tion as the source. I
NTERNAL
synchronizes the given AES3 output rate to
the 8600Si’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 8600Si Input or
S
YNC
I
N
, set
SR S
YNC
to
I
NTERNAL
and select the desired output sample rate.
Format determines if the digital-channel output follows the professional AES3 or
consumer SPDIF standard.