Studio Technologies 76D 2014 - Manual (Page 47)

Model 76D/77 User Guide Issue 11, May 2014
Studio Technologies, Inc. Page 47
for Surround
Sample Rate Conversion
(SRC)
Circuitry associated with stereo input C
can provide sample rate conversion (SRC)
capability. A digital audio signal connected
to that input can have its sample rate and
timing re-synchronized to match the Model
76D’s internal timing. While it would be
nice to proclaim that the engineers at
Studio Technologies came up with a
unique and exotic circuit to perform this
function it’s really not the case. Several
semiconductor companies provide “single-
chip” SRC solutions and an excellent one
from AKM was selected for the Model 76D.
The technical capabilities of the Model
76D’s SRC function is stated in this way:
the sample rate of an input signal can
range from 1/6 to six times the Model
76D’s output sample rate, with the ad-
ditional restriction that it must be no less
than 8 kHz and no more than 216 kHz. The
Model 76D’s output sample rate is deter-
mined by the selected timing reference
(sync) signal and, if required, a configured
value. If a word clock, DARS (AES11), or
AES3 signal is the designated sync source
its rate will be the Model 76D’s output
sample rate. If a video sync signal is con-
nected, the Model 76D’s sample rate is se-
lected as part of the configuration process.
So in practice what can the SRC function
accomplish? If the output sample rate is
48 kHz then a signal connected to stereo
input C can have a sample rate from 8 to
216 kHz. Or, as another example, if the
Model 76D’s output sample rate is 96 kHz
a signal connected to stereo input C can
have its sample rate range from 16 to
216 kHz.
As useful as allowing one disparate sam-
ple rate to be converted to another, it may
be the ability of the Model 76D’s SRC func-
tion to re-synchronize a signal that proves
most valuable. For example, in typical post-
production and broadcast applications all
signals will have a sample rate of 48 kHz.
A Model 76D and all of its normally con-
nected input signals will be “locked” to the
main timing reference signal that supports
the 48 kHz sampling rate. But, as an ex-
ample, a signal associated with a portable
device, while at a 48 kHz sampling rate,
may not be synchronized (“genlocked”)
to the “house” reference. Connecting this
signal to stereo input C will cause the SRC
function to “lock” it to the Model 76D’s rate,
thus allowing it to be monitored over a
loudspeaker system. In addition, the ste-
reo input C direct monitor output can be
connected to other devices that find need
for the now-synchronized signal. In some
cases it may be useful to connect the
stereo input C direct monitor output to the
input of a signal router, allowing an entire
facility to access the signal.
Model 76D to Control Console
Connections
Figure 6 gives a detailed description of the
signals that connect the Model 76D Cen-
tral Controller to the one or more Model 77
or Model 71 Control Consoles. The Model
76D provides 12 volts DC for use by the
control console’s circuitry. The DC output is
current-limited to minimize the chance that
a short-circuit condition will damage the
Model 76D’s circuitry. An asynchronous,
bi-directional data interface links the con-
nected units. The RS-485 hardware con-
nection scheme operates at a rate of 115.2
kbit/s and uses an 8-N-1 data format. The