To control the musical performance, UBZR1 is using an analog wheel at
the analog keyboard (well it is actually a "slider" type
potentiometer, because that I had available). The keyboard interface
is combining this "Wheel" analog voltage with another voltage coming
from the "Digital-In" module. It generates the larger of the two. The
combined signal, called "Wheel*", can be used to control the amount of
modulation in real-time (provided modulation is enabled).
This combination of keyboard and Digital-In levels allows to force a
"minimum" modulation via the Digital Interface and potentially
increase it via the keyboard.
Modulation in UBZR1 is implemented using a concept of a "modulation
matrix": a set of modulation sources can be "patched" to a set of
A full matrix would imply all n:m combinations are available. However,
there are some considerations, that limit the number of useful
- One source usually modulates one destination only. Exception: vibrato
using VCO3, to modulate the pitch of both VCO1 and VCO2
- More than one source could modulate the same destination
simultaneously, although not likely more than two
- If there is overlap between sources and destinations, then some
combinations do not make sense. E.g. if VCO3 is source, it does not make
sense to modulate VCO3 pitch.
The implementation specifics:
- Mapping from source to destination does not need to be the same for
- If all mod. sources are current sources, then summing two or more
sources is simple, to modulate one destination. The destination just
has to provide a suitable input summing resistor.
UBZR1 has the following modulation sources:
- VCO3 current output O1. As VCO3 can be used as a low frequency
oscillator (LFO), this source is important for vibrato type
- VCO2 current output O1. VCO2 can be used for occasional special
modulation situations, because VCO2 usually runs at audio
- ADSR2. ADSR2 timings and contour
can be set independently from ADSR1. UBZR1's implementation is
specific because ADSR2's voltage contour output is not used
directly to modulate. Rather, ADSR2 steers an exponential current
source. This allows both for very smooth and also very strong
In fact, the exp. current source can be thought of an oscillator
with zero frequency. A polarity switching logic signal determines
the "phase". This allows to deliver also an inverted contour.
Above diagram shows the symmetry of the exp. current source behind
ADSR2 and the VCOs and the Noise sources, whose VCA output currents
are also driven by exponential current sources
- Noise current output OP/R, which offers the pink or red "wave
forms". This is useful for random type modulation.
The overall amount of modulation can be controlled by the Wheel*
signal, which can be controlled both by the keyboard and by the
Note that VCO1's O1 current output is not available as modulation
source, because it is used for the ring-modulator functionality
(together with VCO2).
The following diagram shows the four audio generating modules
(VCO1-3 + Noise), the voltage controlled filter and their modulation
UBZR1 has the following modulation destinations:
- VCO1 exponential (i.e. Volt/Octave) frequency modulation
- VCO1 and VCO2 linear frequency modulation. This does not change the
average pitch and is well suited for vibrato
- VCO1 rectangle pulse width modulation
- VCO2 exponential frequency modulation
- VCO2 rectangle pulse width modulation
- VCO3 exponential frequency modulation
- Filter exponential frequency modulation
Modulation Matrix Detail
The chosen implementation of the matrix is a compromise. There are
multiplexer switches per source and a fixed "wired" matrix, with
choices of "useful" combinations. The four multiplexers can not be
switched independently, but are rather coupled in pairs:
- Pair A: the sources VCO3 and VCO2 go together, and
- Pair B: the sources ADSR2 and Noise go together.
Note that for pair A, there are two unused states.
The four multiplexers are controlled by 3-bit logic signals, three
bits per pair.
Modulation Matrix Concept
The following table shows another representation of the chosen matrix.
- "-" marks combinations which do not make sense, because a source
would modulate itself
- "sym." are combinations that would be redundant because of symmetry,
i.e. you could swap VCOs 1 and 2, because they provide the same
- "?" denotes combinations that might be useful
- Arabic numbers indicate the state of a multiplexer switch pair. For
example A1 stands for state 1 of pair A, B1 stands for state 1 of
pair B. The choice of numbers is arbitrary. State "0" does not
appear in the table because it stands for the modulation "off" state
= no modulation from these two sources
- "n.a." are combinations that might be useful, but are not available
because there are no more multiplexer switch states available.
Please note, that VCO3 can run both as low frequency oscillator
(LFO) and at audio frequencies. Thus, VCO3 could be used for vibrato effects, when run in LFO mode.
VCO2 can only run at audio frequencies. When used as modulation source
in combination with VCO3 (state A5) , there can be chaotic sound
effects because of non-linear feed back.