Studio Technologies ISS - Manual (Page 18)

ISS User Guide Issue 3, June 1990
Studio Technologies, Inc. Page 19
ISS
The ISS utilizes an internal operating level
of –6dBu. This keeps adjacent positions in
the ribbon cable bus from significant cou-
pling. The logic signals are asynchronous,
very low speed, and physically separated
from the audio signals. Power and ground
connection were kept off of the ribbon cable
bus to minimize the chance of current
(ground) loops. For your interest, Figure 2,
located at the end of this manual, describes
the signals that are carried on the ribbon
cable bus.
Crossfade Speed
We at Studio Technologies hope that the
crossfade times we have selected will be
right for you. If for some reason you have to
change one or more of the speeds, we will
now describe how to do it. The crossfade
circuitry is contained on the Crossfade
Card, and is discussed in depth in the
circuit description section of this manual.
Three crossfade speeds are used to opti-
mize the audio output signal transition
between simulated and real stereo. Logic
circuitry on the Crossfade Card selects
which speed is appropriate for the opera-
tional situation. The SLOW speed is used
in two situations: the first is going from the
simulating stereo from left or right back to
a stereo input signal; the second is going
from a stereo input signal to simulated
stereo from left when there is a two channel
mono input signal. The FAST speed is used
when the input signal goes from a left and
right stereo input (not simulating) to left
input only, or right input only (going to
simulating stereo from left or right only
input). FAST is used so that the listener
hears only a minimal loss of left or right
channel audio, while the simulated stereo
is coming on line. The IMMEDIATE speed
is used whenever Remote Control Enable
is active. The ISS assumes that the remote
control input signals for Sim from Left and
Sim from Right are very precise and do not
require a time lag as a crossfade is per-
formed. Note that the IMMEDIATE speed is
really just a fast crossfade. No audio clicks
are created during the transition.
The speeds are created in the Crossfade
Card circuitry using simple resistor/capaci-
tor combinations. The SLOW speed is
created with resistor R7 and capacitor C7.
An analog switch adds resistor R9 in paral-
lel with R7 to create the FAST speed. An-
other analog switch adds resistor R8 in
parallel with R7 to create the IMMEDIATE
speed. You can see that all three speeds
are based on the SLOW rate. Changing R7
will change all three speeds. Now do you
really want to change the SLOW speed?
Anyway, choose the speed(s) you want to
change.
If you want to change the SLOW speed,
remove R7 and increase its’ value if you
want a slower speed (longer RC time con-
stant), or decrease its’ value if you want to
speed it up (shorter RC time constant).
Now check the FAST speed and see what
effect the new R7 value has made. If the
FAST speed is now not to your liking, re-
move R9 and replace it with a revised value.
Now check the IMMEDIATE speed. Adjust-
ing R7 really shouldn’t greatly effect the
IMMEDIATE speed, but if it does, remove
R8 and replace it with a revised value.
If SLOW is OK but you want to change the
FAST speed, remove R9 and increase its’
value if you want a slower speed (longer
RC time constant), or decrease its’ value
if you want to speed it up (shorter RC time
constant).