GA3219 / GA3218 / GA3217 Preliminary Data Sheet
6. Signal Path
There are two main audio input signal paths. The first path contains the Front
Microphone and second path contains the Rear Microphone, Telecoil or Direct
Audio input as selected by a programmable MUX. The front microphone input is
intended as the main Microphone audio input for single microphone applications.
In FRONTWAVE operation, a multimicrophone signal is used to produce a
directional hearing instrument response. The two audio inputs are buffered,
sampled and converted into digital form using dual A/D converters. The digital
outputs are converted into a 32kHz or 16kHz, 20-bit digital audio signal.
Further IIR filter blocks process the front microphone and rear microphone signals.
One biquad filter is used to match the rear microphone's gain to that of the front
microphone. After that, another filter is used to provide an adjustable group delay
to create the desired polar response pattern during the calibration process.
In the Telecoil mode gains are trimmed during Cal/Config process to compensate
for microphone/telecoil mismatches.
The FRONTWAVE block is followed by four cascaded biquad filters: "pre1", "pre2",
"pre3" and “pre4". These filters can be used for frequency response shaping before
the signal goes through channel and adaptive processing.
The channel and adaptive processing consists of
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frequency band analysis
1, 2 or 4 channel WDRC
8 logarithmically spaced band frequency shaping (graphic EQ)
128 frequency band adaptive noise reduction
frequency band synthesis
phase cancellation adaptive feedback reduction
After the processing the signal goes through two more biquad filters, "post1" and
"post2", the Wideband Gain and Volume Control.
These biquad filters are followed by the AGCo block, two more biquad filters,
post3" and "post4", and the Peak Clipper. The last stage in the signal path is the
D/A H-bridge.
Proprietary and Confidential 32718 - 2
February 2005
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GENNUM [ GENNUM CORPORATION ]
