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INSIDE THE SYNTHESIZER
The S1 synthesizer is an analog instrument (not including the MIDI Converter of course). Most
parameters such as frequency, amplitude, resonance (Q-PEAK), attack time, decay time, etc. are
adjustable via potentiometers on the front panel and can also be voltage controlled via respective CV
inputs.
The main voltage regulator is equipped with a highly stable reference circuit with a stability of 20ppm/deg C
to guarantee long term stability. In addition, great attention has been taken to design of the oscillators to
achieve the highest possible frequency stability; a carefully chosen compensation circuits has been designed
by simulation tool and practically verified to achieve high stability throughout the entire temperature range.
In addition to the application of know-how from the analogue field, modern simulation tools have been used
to optimize and verify the characteristics and performance of all circuits inside the S1.
Since the filters are among the most dominant sound processors in an analog synthesizer great effort
have been taken in their design both in regard to the form of simulation and practical listening tests
with the object of being able to offer two completely different types of acoustical characteristics in the
LPF and MMF. Via countless testing and listening it was determined that the filters, in addition to the
customary 12 and 24dB/octave slope, must also have a 36dB/octave slope. The difference between 24
and 36dB slope may seem to be slight
but is highly pronounced to a listener and offers new and highly
useful possibilities in sound modification.
Envelope generators have been developed by simulation in a computer environment. All the
parameters can be voltage controlled within a large time range; Attack, Decay, Release times are
adjustable from 0.5 milliseconds (actually 350 microseconds) to 20 seconds.
S1 is a so called semi-modular synthesizer which means that all modules, e.g. oscillators, filters, etc. are
interconnected in a certain configuration. The configuration can be altered using patches. Connections
between the different modules can be broken and routed to other inputs or outputs. For example, to cross-
connect the filters, the MULTI-MODE FILTER external audio input is connected to the LOWPASS FILTER
audio input which can produce unexpected effects such as the generation of sub-octave tones. The list of
possible configurations is, of course, very long so the following is a description of the constituent parts of
the instrument, i.e. the modules.
OSCILLATORS
There are three oscillators that are largely identical (except that OSCILLATOR1 that can be used as
an extra LFO in the LF mode) with five basic waveforms; sine, triangle, sawtooth, variable pulse, and
triangle mixed with variable pulse.
Sine Waveform
An ideal sine wave is the most fundamental signal (tone) that contains only the basic tone. In an analog
synthesizer the sine wave is produced by synthesis that results in a signal that is not completely perfect.
See the illustration below. The left side shows the sine signal and the right side shows its spectrum density.
Aside from the basic signal (440Hz) there are a number of harmonic overtones.
OSCILLATOR OUTPUT, SINE, A440
O
U
TP
U
T
(V
ol
ts
)
5.0
2.5
0.0
-2.5
-5.0
-7.5
3.00
4.00
5.00
6.00
7.00
8.00
Time (milliseconds)
7.5
dB
V
rm
s
0.0
-10.0
-20.0
-30.0
-40.0
-50.0
-60.0
-70.0
-80.0
-90.0
1.0k
3.0k
5.0k
7.0k
9.0k
11.0k 13.0k 15.0k 17.0k 19.0k
Frequency (Hz)
440.00 Hz
