Studio Technologies 76D V.2.02 - Manual (Page 39)

Model 76D/77 User Guide Issue 2, June 2009
Studio Technologies, Inc. Page 39
for Surround
After a successful system power-up se-
quence normal operation will then com-
mence. Should a problem be encountered
during power up one of two error codes
may show on the Model 77’s 4-digit display.
If Err1 displays it indicates that communi-
cation is not taking place with the Model
76D. The most likely cause would be incor-
rect wiring of the data pair linking the two
units.
Err2 indicates that the Model 76D
is having problems with its internal logic
device. (A high-speed field-programmable
gate array (FPGA) serves as the digital
“heart” of the Model 76D and without it no
audio activity can occur.) The only way to
remedy this condition is to first try remov-
ing and reconnecting mains power. (And
that’s a long-shot as to whether that would
accomplish anything.) If the error code
continues to be displayed the Model 76D
must be returned to the factory for service.
Note that for the vast majority of Studio-
Comm systems neither of these error
codes, especially Err2, will ever appear.
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 clock. 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 solu-
tions and an excellent one from AKM was
selected for the Model 76D. The technical
capabilities of the Model 76D’s SRC func-
tion 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 additional restriction that it
must be no less than 8 kHz and no more
than 216 kHz. The Model 76D’s output
sample rate is determined by the external
timing reference (sync) signal and, if re-
quired, a configured value. If a word clock,
DARS (AES11), or AES3id signal is the
designated sync source its rate will be the
Model 76D’s output sample rate. If a video
sync signal is connected, the Model 76D’s
sample rate is selected as part of the con-
figuration 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
signals will have a sample rate of 48 kHz.
A Model 76D and all 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