Wersi DX 400, Assembly Manual

Page: 5 / 68

AM 334-01-502
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synthesizers to conventional musical instruments are
possible through software.
A further advantage of this system is that a given sound
quality, once achieved and filed as software, will be the
same when reproduced by an organ in the series, since
hardware variations will have virtually no effect on the
sound properties.
Additional special effects can be achieved through further
processing of the digitally developed voices via a voltage-
controlled filter (VCF) and a phase vibrato (Wersivoice)
circuit.
Apart from its contrast to other organ systems, the DX
concept offers the most possibilities in terms of sound and
functions, and is the most flexible concept for the electronic
production of individual musical voices yet presented.
Ill. The DX System Block Diagrams
1. Block Diagram of the Complete Organ
Fig. 1 is a block diagram of the complete DX series organ;
the following is a brief explanation of the organ's functions:
The master central processing unit (CPU), located on the
master processor board, is the control center of the organ.
The CPU obtains, via the peripheral bus, all the information
it needs to control the immediate production of any sound
the player selects; this is because the CPU continuously polls
the instantaneous status of all selector switches, drawbars,
controls, and keyboard and pedal contacts. And while it's
doing that
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it also sends back the necessary signals to
illuminate the light-emitting diodes (LED's) in the activated
switches.
The CPU transforms the incoming data into the appropriate
instructions to send via the master bus to circuits such as the
VCF, slaves, etc., which generate analog (audio) signals
based on these instructions. From there on out, it's all
analog; the audio bus sums all the audio signals, which then
are amplified and applied to the speaker to produce the
desired sounds.
Block Diagram of the Slave Processor
Fig. 2 is a block diagram of a slave processor. The DX organ
uses up to five slave processors to produce sounds.
Each slave generates as many as four free-programmable
complex voices, each with two simultaneous sound com-
ponents. The coordination of these, via the master processor,
can arbitrarily stem from the upper manual, lower manual,
auto-accompaniment or pedals.
Since every voice consists of two envelope-shaped tone
components each, eight audio channels are required to
produce four voices. By this means, all voices can be
constructed from two components, for example, draw-bars +
percussion, piano + strings, even smooth string tones + the
plucked tones of a guitar.
At the moment a keyboard or pedal key is depressed, the
master CPU loads a "slave program," as well as data which
will set the sound parameters, into the slave processor's 2-
port random access memory (RAM) via the master bus. The
bus switch then transfers the RAM data lines to the slave bus
during the slave's internal processing sequence.
To enable a maximum transfer of data, the 2 MHz clock
frequencies of the master CPU and the slave CPU are shifted
a half cycle out of phase with each other. Accordingly, large
blocks of data-for complex voices, for example-can be
transferred between the processors at a simulated 4 MHz
rate. The bus switch is constantly switching the RAM from
the master bus to the slave bus and , consequently, both
processors continuously receive RAM control data.
After the master CPU loads the RAM, the slave CPU carries
out the internal slave program. Five timers set up the readout
speed according to the program. Four timers determine the
pitch (according to the readout of the RAM sound parameter
tables) and the fifth determines the repeat frequency for the
envelope control count.
The direct memory access (DMAC), under control of the
timeout information and the sequence logic, enables a direct
readout of the RAM sound parameter table apart from CPU
influence.
The sequence logic, via a write (WR) signal, loads the
direct-read digital data for four 2-component voices, one
after the other, into eight signal digital-to-analog (DAC)
converters. On a data transfer (XFER) signal, the signal
DAC's convert the digital data into analog signals. The
interval memory loading and the direct timer-controlled
readout of the digital data result in a jitter-free analog signal
of outstanding purity, not affected by the internal cycling.