S Y N T H E S I S B O A R D - Philips SPENDEX 40 Maintenance Manual

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NATO CONFIDENTIAL
S P E N D E X 4 0 U A 8 2 5 1 / 0 0 A N D / O l L I M I T E D M A I N T E N A N C E M A N U A L
4 . 4 S y n t h e s i s b o a r d
4 . 4 . 1 D F T - p r o c e s s o r
Every 22.5 ms the contents of the segmentation buffer on the analysis
board are presented 128 times to the DFT-processor. The DFT-processor
determines the spectrum by means of a Discrete Fourier Transformation
and passes the result on to the pitch processor in serial form.
4 . 4 . 2 P i t c h p r o c e s s o r
Via an harmonic filtering method the pitch processor determines the
pitch from the amplitude peaks of the spectrum. As soon as the pitch
processor has calculated the pitch, the vocoder controller will be
interrupted (INTPIT). After acceptation of the interrupt the vocoder
controller will take over the pitch, smooth it and store it in the
pitch buffer of the analysis board.
4 . 4 . 3 S y n t h e s i s p r o c e s s o r 1
The moment synthesis processor 1 is ready to receive a frame, the
vocoder controller is interrupted (INTSYN); then the vocoder
controller collects the oldest frame from the synthesis part of the
vocoder data memory and passes it on to synthesis processor 1. As
soon as synthesis processor 1 has received the frame, the first part
of the synthesis starts. When the signal NFRN is activated synthesis
processor 1 is interrupted. After acceptation of the interrupt the
results are sent to synthesis processor 2.
4 . 4 . 4 S y n t h e s i s p r o c e s s o r 2
Synthesis processor 2 generates the 8 bit samples initially coded in
a-law. Then the samples will be passed on in serial form to the
D/A-converter on the connecting board.
4 . 4 . 5 V o c o d e r c o n t r o l l e r
The vocoder controller takes care of the control of the vocoder and
exchanges via the vocoder bus system data and control signals with
the various circuits within the vocoder.
Furthermore the vocoder controller looks on transmitting side after
the transfer of frames to the comsec controller and on receiving side
after the take-over of frames from the comsec controller.
After acceptation of the interrupt signal INTCO, which comes from the
comsec controller, the vocoder controller will collect a frame to be
sent from the analysis part of the vocoder data memory and transfer
this frame to the comsec controller or take over a received frame
from the comsec controller, correct its errors, if any, and then
store it in the synthesis part of the vocoder data memory.
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NATO CONFIDENTIAL