GA3219 Datasheet, PDF (9/14 Pages) Gennum Corporation – Venture-TM Digital DSP System

VENTURE GA3219
signal processing, but can be used to store additional
information related to the associated biquad.
The underlying code in the product components
automatically checks all of the filters in the system for
stability (i.e., the poles have to be within the unit circle)
before updating the graphs on the screen or programming
the coefficients into the hybrid. If the Interactive Data Sheet
receives an exception from the underlying stability checking
code, it automatically disables the biquad being modified
and display a warning message. When the filter is made
stable again, it can be re−enabled.
Also note that in some configurations, some of these
filters may be used by the product component for
microphone/telecoil compensation, low−frequency EQ, etc.
If this is the case, the coefficients entered by the user into
IDS are ignored and the filter designed by the software is
programmed instead. For more information on filter design
refer to the Biquad Filters In PARAGON^® Digital Hybrid
information note.
Volume Control
The Volume Control (VC) can be either external or
programmable. If VC is programmed for external operation,
a variable resistor should be connected to the 9 bit A/D
converter.
The external VC can be configured to work with either a
two−terminal 200 kW variable resistor or a three−terminal
0.1 MW – 1 MW variable resistor. In two−terminal
configuration, the VC is connected between GND, Vreg and
the VC input.
If using a two−terminal VC, it must be calibrated before
use. Calibration is not necessary with a three−terminal
connection. Hysteresis is built into the VC circuitry to
prevent unintentional volume level toggling. A log taper
potentiometer is recommended so that gain in dB would be
linear with potentiometer rotation. The range of VC is
adjustable and can be set between 1 dB (min) and 42 dB
(max).
AGC−O and Peak Clipper
The output compression−limiting block (AGC−O) is an
output limiting circuit whose compression ratio is fixed at
∝:1. The threshold level is programmable. The AGC−O
module has programmable attack and release time
constants.
The AGC−O on Venture GA3219 has optional adaptive
release functionality. When this function is enabled, the
release time varies depending on the environment. In
general terms, the release time becomes faster in
environments where the average level is well below the
threshold and only brief intermittent transients exceed the
threshold.
Conversely, in environments where the average level is
close to the AGC−O threshold, the release time applied to
portions of the signal exceeding the threshold is longer. The
result is an effective low distortion output limiter that clamps
down very quickly on momentary transients but reacts more
smoothly in loud environments to minimize compression
pumping artifacts. The programmed release time is the
longest release time applied, while the fastest release time is
16 times faster. For example, if a release time of 128 ms is
selected, the fastest release time applied by the AGC−O
block is 8 ms.
Venture GA3219 also includes the Peak Clipper block for
added flexibility.
Memory Select Switches
One or two, two−pole Memory Select (MS) switches can
be used with Venture GA3219. This enables users
tremendous flexibility in switching between configurations.
These switches may be either momentary or static and are
configurable to be either pull−up or pull−down through the
settings tab in IDS.
Up to four memories can be configured on Venture
GA3219. Memory A must always be valid. All memory
select options are selectable via the settings tab in IDS.
Momentary Switch on MS
This mode uses a single momentary switch on MS (Pin4)
to change memories. Using this mode causes the part to start
in memory A, and whenever the button is pressed, the next
valid memory is loaded. When the user is in the last valid
memory, a button press causes memory A to be loaded.
This mode is set by programming the ‘MSSMode’
parameter to ‘Momentary’ and ‘Donly’ to ‘disabled’.
Example:
If 4 valid memories: ABCDABCDA…
If 3 valid memories: ABCABCA…
If 2 valid memories: ABABA…
If 1 valid memories: AAA…
Momentary Switch on MS, Static Switch on MS2 (Jump
to Last Memory)
This mode uses a static switch on MS2 (Pin5) and a
momentary switch on MS (Pin4) to change memories. If the
static switch is OPEN, the part starts in memory A and
behaves like momentary, with the exception that memory D
is not used. If the static switch on MS2 is set to HIGH, the
part automatically jumps to memory D (occurs on start−up
or during normal operation). In this setup, the momentary
switch’s state is ignored, preventing memory select beeps
from occurring. When MS2 is set to OPEN, the part loads in
the last select memory.
This mode is set by programming the ‘MSSMode’
parameter to ‘Momentary’ and ‘Donly’ to ‘enabled’.
Example:
If MS2 = OPEN and there are 4 valid memories:
ABCABCA…
If MS2 = OPEN and there are 3 valid memories: ABABA…
If MS2 = HIGH: D…
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