GA3216 Datasheet, PDF (10/14 Pages) Gennum Corporation – FOUNDATION-TM Digital Single or Dual Channel DSP Compression System

The I/O characteristic of the channel processing can be
adjusted in six ways:
• squelch threshold (SQUELCHTH)
• low level gain (LLGAIN)
• lower threshold (LTH)
• high level gain (HLGAIN)
• upper threshold (UTH)
• compression ratio (CR)
During Parameter Map creation, constraints are applied to
the compression parameters to ensure that the I/O
characteristics are continuous. In both Programmable mode
and Trimmer mode predefined parameter adjustments
support two popular styles of compression ratio adjustment:
• The compression region of the I/O curve pivots about
the upper threshold. As the compression ratio trimmer is
adjusted, high-level gain remains constant while the
low-level gain changes.
• The compression region of the I/O curve pivots about
the lower threshold. Low-level gain remains constant as
the compression ratio trimmer is adjusted.
The two compression channels can be controlled in tandem
using a common wideband level detector, or independently
using dedicated in-channel level detectors. Parameters
such as low level gain, lower threshold and compression
ratio can be combined and controlled by a single trimmer.
The squelch region within each channel implements a low
level noise reduction scheme (1:2 expansion) for listener
comfort. This scheme operates in quiet listening
environments (programmable threshold) to reduce the gain
at very low levels.
Single-channel compressor operation is supported by
disabling the band split filter and one of the channel
compressors. The remaining compressor can be configured
as a wide-dynamic-range compressor (WDRC), or as an
input compression limiter (ICL).
HRX HEAD ROOM EXPANDER
The GA3216 has an enhanced Head Room Expander
(HRX) circuit, which increases the input dynamic range of
the FOUNDATION Digital without any unwanted audible
artifacts. This is accomplished by dynamically adjusting the
preamplifier’s gain and the post-A/D attenuation depending
on the input level.
TELECOIL PATH
The telecoil input is calibrated during the Cal/Config
process. To compensate for the telecoil/microphone
frequency response mismatch, a first order filter with 500Hz
corner frequency is implemented. Through ARKonline it is
possible to implement a telecoil compensation filter with an
adjustable corner frequency. To accommodate for the gain
mismatch, the telecoil gain is adjusted to match the
microphone gain at 500Hz or 1kHz (default) and is
selectable in ARKonline. There is also a telecoil gain
adjustment parameter, which can be enabled in ARKonline
and set in IDS that will allow for manual adjustment of the
telecoil gain compensation.
VOLUME CONTROL & TRIMMERS
All parameters can be controlled via the SDA or assigned to
the trimmers. The four trimmers have flexible parameter
assignments so any of the four trimmers can be assigned to
any available parameters (A complete list of parameters is
available on ARKonline).
Both the external VC and trimmers can be configured to
work with either a two-terminal 200kΩ variable resistor or a
three-terminal 0.1MΩ – 1MΩ variable resistor. The volume
control should have a log taper, while the trimmers should
have a linear taper.
In two-terminal configuration the trimmers and VC are
connected between GND and the trimmer Input and in
three-terminal configuration between GND, Vreg and the
trimmer Input. To enable the device to use two terminal
trimmers, in IDS under Settings in the Cal/Config menu,
click the trimmers tab and select two terminal trimmers. If
using two terminal trimmers, they must be calibrated before
use. Calibration is not necessary with three terminal trimmer
pots. Hysteresis is built into the circuitry to prevent
unintentional level toggling.
EQUALIZATION FILTERS
There are five equalization filters provided on the
FOUNDATION Digital for additional frequency shaping.
Each EQ filter has three adjustable parameters, centre,
depth and Q. One of these parameters can be selected as
trimmer adjustable for each filter. For added flexibility it is
possible to combine EQ2 and EQ3 or EQ4 and EQ5
together and have them adjusted by one trimmer.
AGCo
The AGCo module is an output limiting circuit with a fixed
compression ratio infinity:1. The limiting level is
programmable as a level measured as dB from full scale.
0 dBFS is the maximum output of the device. The AGCo
module has its own twin level detector, with programmable
attack and release time constants.
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